BMC 1.5 cooling issue

[Amulet]

Hi all

 

Been a quiet reader on this forum for a while. It was time for me to get in enough trouble to need to post for myself!

 

I have owned a boat with 1.5 BMC from 1980 since november and only started really cruising recently.

Did basic maintenance after buying: oil, filters, injection tweaking, ...

It is keel cooled.

 

Last time we took it for a (longer) cruise of about 6 hours. It started overheating after 3-4 hours: the coolant just came bursting out of the tank through the small hole in the filling cap. It almost emptied the tank, few liters came out pouring in the air, mid-cruise. There was a loooot of pressure in there.
We let the engine cool off, refilled the tank with fresh antifreeze and went on, keeping a close eye on the engine (we also opened up the hatches to let it cool etc). It happened again after a few miles and after refilling again, it even cut twice (seized? idk). We let it cool down for a few minutes after both "seizes" before restarting; we then decided we had to run it really slowly on the way back. It proceeded for another 2 hours of navigating without trouble: at maybe 1-2 km/h but it just went on at that pace.

Engine didn't seem too hot then.

Smoke was coming out of the exhaust at that point but I get that every time at lower RPM, I feel.

 

I was running the engine at maybe 3/5th of its capacity before the incident, maybe even a bit less but it was a hot day + we never took it out for that long.

 

I have 4 suspects:

 

1 The thermostat could have decided to retire? 

2 Air in the system?

3 The water pump shall be changed? 

4 The hoses are clogged?

 

None of the above have been checked on by anyone for a few years, I can guarantee.

 

Option 1 wouldn't be too much of a pain (lol I feel like I'm going to jynx this)

But in that case; can anyone tell me which thermostat I need please? 74 degrees, 82? What would you recommend?

Any references on what to buy? I am actually in Belgium, I only manage to find UK based sites which don't ship here  

So if you can help me with dimensions, references to the right thermostat, shoot! I guess it is a generic thermostat, but which reference, I got no idea

 

Same goes for option 3 and the water pump, I find it quite difficult to find parts for the BMC engines outside of the UK, any leads there maybe? 

 

As for option 2 and 4, they seem pretty straight forward. Any recommendations from anyone, anyway?

I have been reading about radflush and other products, even using a high pressure washer? 

Or should I take it all apart manually? 

 

Anyone has another suspect in mind? 

 

Thanks a lot for anyone reading or answering! 

 

[Tony Brooks]

Yes, the head gasket failed, but 1 and 2 need checking and eliminating first. As does an undersized ski tank. Please supply the dimensions of the skin tank (very few canal boats use a keel cooler) and how hard/fast you were driving the boat on what type of canal. The wide & deep continental canals may allow you to    drive the engine with an undersized skin tank hard enough to boil it.

 

3 and 4 are unlikely or very unlikely on a skin tank cooled BMC because the hoses are so large and the water pump typically uses a cast iron impeller, they very rarely lose their impellers. However, they do eventually leak and that eventually leads to boiling. So check the front of the engine, below the water pump, top, pulley for signs of a leak - antifreeze or rusty streaks, or actual water droplets.

 

For completeness to help others. 3 & 4 would not be unreasonable on a direct raw water cooled or indirect raw water cooled (heat exchanger) engines because they have water pumps that have rubber impellers that shed vanes and block bends in small diameter hoses.

 

The engine was designed for a car, so with a properly designed skin tank a car thermostat should be fine at around 82 degrees. Any decent local car parts place should be able to match it up. It is nothing special. Yours may be an old bellows type, but the new one will look very different because it will be a Waxstat. The 72 degree stats are used on direct raw water cooled engines to minimise internal furring, or on boats using a calorifier for hot domestic water to reduce the dangers of scalding from the taps a little. It is NOT what is known as a bypass thermostat that some cars use.

 

I have never had to pressure wash a skin tank or cooling system, but have used a hose to reverse flush skin tanks and engine blocks - do that when the thermostat is out. using a cooling system flush additive will do not harm, but is unlikely to solve the problem - it will probably make you feel that you have done something.

 

Calcutt Boats of Southam specialise in BMC 1.5 and 1.8 parts, but the problems caused for imports.exports by Brexit may make them unwilling to post to Europe, you can always ask them.

 

Calcutt Boats Ltd
Tomlow Road
Stockton
Southam
Warwickshire
CV47 8HX
United Kingdom

Tel: +44 (0)1926 813757

 

Calcuttboats.com

 

 

[Amulet]

I didn't expect such a fast reply, thank you Tony!!

 

I'm happy to read 3 and 4 are unlikely; they would be the most difficult to sort out.

 

I'll be replacing the thermostat first. I wanted to take it out yesterday when I was at the boat but I was lacking tools and the boat is at an hour drive. That's why I would have liked to have a thermostat at hand next time I am going.

But I now know what to look for, thanks! It's just what I thought indeed.

 

The skin tank takes maybe 20L, it is hard to give you an exact approximation as I am not at the boat right now. But after "spitting" its coolant last time, I had to retop at least 15L

How could I check the dimension, btw? Purging the whole system and refilling it? I don't feel like there is a jauge somewhere to check the level. Is it like a car or motorcycle, with a minimum and maximum amount to put into it?

Tbh I just filled it up to the top of the filling cap... Maybe I put in too much? 

My mechanical knowledge consists of cleaning dirtbike carbs or changing their wheels... Bear with me Tony 🤣

 

As I said we were at maybe 3/5th or MAXIMUM 3/4th of engine capacity on a rather large Belgian river (Haute-Sambre), cruising at maybe 6-8 km/h. Not many obstacles or traffic. Sometimes more than an hour until the next lock; so a constant "higher" RPM.

 

I'm attaching a few pictures, should have done that earlier. I feel like I do have a heat exchanger? But still it is keel cooled? 

Don't bother with the dirty water on the pictures, they are old pics. Boat is still dirty, but water is now gone and bilge pumps are sorted. (also the oil in the water was from service, not leaking) (I am working on the "dirty" part as well no worries)

 

I'll check for a leak on the water pump next time, after:

1 changing the thermostat

2 draining and flushing the whole system

3 refilling and purging it

 

I feel like I'll have to keep an eye on the amount of antifreeze solution I refill it with? But how? haha

(it is empty at the moment, I drained it yesterday to try and remove the thermostat)

 

Yeah I had my eyes on Calcuttboats for a while, but outside-UK shipping is a pain in the *** now  I'll send them an email to check for further possibilities. That could come in handy someday, anyway. I hope not too soon ^^

 

Thanks again for your reply and have a great sunday!

 

 

[Tony Brooks]

We need the dimensions of the skin tan (preferably in imperial, but we can convert from mm) to calculate its outer surface area - then it is 1 sq ft per HP.

 

20 litres does not sound like a very large skin tank to me. The thickness does not matter, apart from the thinner, the better so hot coolant can't keep away from the outer (hull) surface.  We just need surface area.

 

If your present stat is a waxstat the apparent boil up may have caused it to shed wax so it is now not opening soon enough - or from pre your ownership incidents.

 

I see that you have a capillary temperature gage. Does that not work to warn you of overheating? If not I would suggest changing it for an electrical one.

 

I can see no signs of a second water pump that you would need if it did have a heat exchanger, but then I can't be sure that what I can see are the pipes/hoses from engine to skin tank. I can not see any pipes running to an actual keel cooler under the boat.

 

Just ask and car spares place for a generic non-bypass thermostat of around 82 degrees or less. It is nothing special.

[Tony Brooks]

Just spent a fair time studying the photos. I think this is a cruiser and I can see what I think are coolant pipes running down to the hull to what I suspect is a keel cooler sited under the boat, but if I am correct then I would have preferred the cooler to be tucked beside any keel to help protect it. That then makes the 20 litres a bit more believable because keel coolers on cruisers are often four brass/copper pipes about 15mmin diameter, about 4 or 5 ft long, running between headers. these would be the larger white pipes connected to convoluted hoses.

 

If I am correct, this then raises another potential cause, depending upon how he pipes are secured in the headers. One popular type from the 70s secured the pipes into the headers by rubber washers that were compressed onto the pipe by hollow bolt like things. These can leak, especially if a pipe has been bent in some way.

 

I would suggest that you fill the system and do a cooling system pressure test, leave it for several hours under pressure and see if the level drops - it should not as long as you do it cold. You can spend that time checking for leaks from the water pump and all the other hose joints. Note - be wary of putting so much pressure in the system it lifts the water pump seal, so the pump leaks. I would not go higher than 15 t 20 psi. The cooling system pressure cap (filler) would normally be around 6 psi on a marine BMC 1.5, but I am not sure your system is pressurised. I can't see the filler cap so don't really know.

 

 

[Amulet]

The boat is an Amulet Vlet 800

 

Here's another picture where you can see the thick white pipes a bit better 😉 

Indeed they go underneath the boat and then back in it 

 

 

But they seem to go through a heat exchanger (on the left side). Or am I wrong?

 

The filling cap is one of those, copper if it makes any difference. It's situated on the outside of the boat:

 

 

 

 

I just ordered another gauge for the temperature. The one that's installed doesn't work; I'll see if a new one fixes it. But I'd rather have one for the next cruises for sure. About that matter, is there a "wireless" option you would recommend? I'm always navigating from the outside but the gauges are on the inside ... (2 helms available) So I would love to have some kind of portable device to take with me outside when navigating and keeping an eye on engine stats. I know the guy I took lessons with had one, but I am struggling to find any similar device ... (the gauge connected to the thermostat sent its data live and wirelessly to a little portable, battery operated device)

 

I'll also have a look at every hose next time, just to make sure it's all still tight and not hardened.

 

As for the pressure test, how should I proceed? I know what I should do on a car or bike; I have no idea where to measure it from in this case, or what tool to use (a specific adapter for my manometer?).

And if I keep it between 15-20 psi, the water pump shouldn't leak? Did I understand that correctly? Or will it leak anyway?

 

You deserve to hear this daily Tony; You are awesome!! Thanks for your advice!

 

[Tracy D'arth]

It is a heat exchanger and exhaust cooler on the port side of the engine. What is that small pipe connected to it near the front?

The problem will be either lack of sufficient heat exchange area to the outside water, lack of sufficient flow through the cooling system, or a leaking head gasket/cracked head casting pressurising the cooling system and blowing water out.

A faulty stat would boil the engine much faster than you say.

If that is the only filler, vented, then it is not a pressurised system unless there is a pressure cap somewhere else, its an odd arrangement.

Conversely if that filler is not vented at all it is a sealed system with nowhere for expansion or pressure release, very odd.

[Tony Brooks]

The long blue aluminium think on the left where a heat exchanger is usually situated is just a water jacketed exhaust manifold. There is a cover on the front of it that suggest that it could have a heat exchanger core fitted BUT if it had one then there would be two thinner hoses plus a brass water pump driven from the little pulley that you can see in front of the bottom engine pulley. No little hoses, no brass water pump = no heat exchanger.

 

On those manifolds, the pressure cap/filler is usually located on the little oval plate where the vent hose connects.

 

This seems to be a steel cruiser and now I can see there is an internal skin tank, not an external keel cooler. However, all that matters is the surface area or the external face that is probably the hull and the depth of the tank looks excessive for efficient operation. A BMC 1.5 is rated at around 35 bhp at full power and at 4 hp to 1 sq ft of tank area that requires a skin tank area of about 8 to 9 sq feet or roughly 0.8 sq meters/8000sq cm. I am not sure that tank has enough area, plus any inefficiencies involved with it's depth to adequately cool at maximum poser, however you don't use maximum power and speed for long [periods of time very often inland, so a LITTLE less will probably do. You need to measure the tank and work out its surface area of the lower face.

 

You pressure test boat systems just like a car. Seal the filler and pump air into the system. The tester often provides both the seal and a valve for pumping the air in. Unless the hull has rusted through into the skin tank there is virtually no chance of it leaking into the river/canal. I think that now we can see the tank you do not need to pressure test the system unless you are checking for hose leaks. That 15 to 20 psi is just a rough idea, so not fixed in stone. if you do pressure test it, keep an eye under the water pump and let a bit of pressure out if it starts to leak.

 

So we now know that your cooling system is not pressurised and that raises another long shot possibility, but it is unlikely unless you were running flat out for a while. Cooling systems are pressurised to prevent internal hotspots inside the engine boiling, so with no pressurisation those hotspots may boil, but in the early stages the coolant temperature remains normal until the steam pushes a lot of the coolant out, then it boils with clouds of steam.

7 minutes ago, Tracy D'arth said:

It is a heat exchanger and exhaust cooler on the port side of the engine. What is that small pipe connected to it near the front?

The problem will be either lack of sufficient heat exchange area to the outside water, lack of sufficient flow through the cooling system, or a leaking head gasket/cracked head casting pressurising the cooling system and blowing water out.

A faulty stat would boil the engine much faster than you say.

If that is the only filler, vented, then it is not a pressurised system unless there is a pressure cap somewhere else, its an odd arrangement.

Conversely if that filler is not vented at all it is a sealed system with nowhere for expansion or pressure release, very odd.

 

I am sure that pipe is just an air vent/breather, but where it runs to is anybodies guess. I hope the filler pipe, but it may just vent over the side or into the bilge. Apart from the danger of localised boiling when at high powers, I think it should be a totally self venting and reliable system. I don't like river boats operating with no cooling system pressurisation, although it has proven to be fine for UK canal boats because of the limited opportunity for high-powered working.

[Amulet]

43 minutes ago, Tracy D'arth said:

It is a heat exchanger and exhaust cooler on the port side of the engine. What is that small pipe connected to it near the front?

The problem will be either lack of sufficient heat exchange area to the outside water, lack of sufficient flow through the cooling system, or a leaking head gasket/cracked head casting pressurising the cooling system and blowing water out.

A faulty stat would boil the engine much faster than you say.

If that is the only filler, vented, then it is not a pressurised system unless there is a pressure cap somewhere else, its an odd arrangement.

Conversely if that filler is not vented at all it is a sealed system with nowhere for expansion or pressure release, very odd.

 

The small pipe in front (copper with a small textile fitting at the end, top left on my last picture), is coming straight from the skin tank.

 

Indeed it is probably lack of surface area or insufficient flow in the system. I don't think the head gasket was leaking or cracked (before overheating, at least. We'll see how it is now but the "seizes" it went through are not my biggest concern right now, it seems to run flawlessly and without any weird noises)

But "pre-incident" the engine runned like a clock, no overheating, no smoke except at lower RPM's and mostly cold.

 

I'll change the thermostat anyway next time, just to be sure. I'll try to test the old one just for the sake of knowing

Also, I'll have a closer look to try and find a valve on the skin tank or something.

With the help I got here I am now a bit more sure of what I should be looking for  Although, if I can't manage to find one, it might be a weird situation indeed.

 

The filler I use on the outside, at least, is not vented. It has two small holes in it which you normally use to open it with a "special" key. 

On my filler, one of these holes is "see-through", the other one is closed but just deep enough to fit the opening tool. I am not sure if one of these holes is actually supposed to be open or not.

But in the end that hole is where the coolant spilled out of  + also from the sides of the cap, as its o rings have seen better days. I'mplanning on changing them soon. (probably going to renew/change the whole cap system, maybe depending on my findings here and later)

 

 

@Tony Brooks : Thanks, it makes sense! I'll do all which we discussed above and I'll try to measure the skin tank next time.

I know this boat was navigating in the same area since at least 2010. So I would be quite confident on the surface area; I think I might have just pushed the boat a bit over its limits by running it at too high revs for too long. That plus the fact that I wasn't keeping an eye on any temp gauge as I don't have it working... Lessons learned

I will also install a ventilation system; there is already a quite powerful fan sucking air out on starbord. I would like to have one sucking air in on the other side, creating a nice airflow down there.

 

So if it is not pressurised, what is the other long shot possibility? 🙂 I'm afraid I didn't understand that part!

[Tony Brooks]

2 hours ago, Amulet said:

The small pipe in front (copper with a small textile fitting at the end, top left on my last picture), is coming straight from the skin tank.

 

That is very poor then. There would seem to be no high level vent to release any air trapped in the system, as there certainly will be in the top of the manifold.

 

The filler is vented, via the small all through hole, so the system is not pressurised.

 

I very much doubt there is a valve on the sin tank, not least because the vertical hose connections will allow any air to move upwards towards the engine and manifold. How it is supposed to exit the manifold is anyone's guess.

 

I think that I would loosen the hose clip where the braided "overflow" hose and take the copper pipe out of the hose. Then when you fill air has a means of escape. Then run the engine at fast idle until the manifold starts to get warm. That means the thermostat has opened so any air trapped in the engine or pipe work should be in the manifold. Stop the engine and fill the system via your normal filler until coolant flows out of the hose. Reconnect and it should be bled as long as there are no bows in the pipes that can trap air. Personally, I would investigate moving the vent pipe to high up on the main filler pipe so any trapped air has an easy path out of the main circuit.

 

The long shot is that this was caused by localised boiling, within the engine, on certain hotspots like exhaust valve seats and around the injector nozzles under high powers. This is a theoretical risk and I have never come across an instance on UK INLAND boating, but then there are speed limits, even on rivers, but it can not be ruled out. I have had it causing engine damage on BMC 1.5s using DIRECT raw water cooling when a thermostat was fitted. this should NOT apply to your engine, but you might still suffer the localised boiling.

[Tracy D'arth]

45 minutes ago, Tony Brooks said:

 

 

The long shot is that this was caused by localised boiling, within the engine, on certain hotspots like exhaust valve seats and around the injector nozzles under high powers. This is a theoretical risk and I have never come across an instance on UK INLAND boating, but then there are speed limits, even on rivers, but it can not be ruled out. I have had it causing engine damage on BMC 1.5s using DIRECT raw water cooling when a thermostat was fitted. this should NOT apply to your engine, but you might still suffer the localised boiling.

Localised boiling likely especially in that exhaust cooler if there is any air trapped in it.

[Amulet]

Thanks for your help, the both of you

 

I had the opportunity to go to the boat yesterday

I'll share my findings:

 

- The thermostat was a 74 degrees... I ordered an 82 to replace it

It seemed fully gripped between the open and closed position, not much movement, warm or cold

Testing it in 80° water confirmed that it is not working anymore. Anyway, pre-incident reason or not, it will be changed for the right one, so that's checked

 

- The skin tank measurements: 125x75 cm. So it's approximately 0.9 sq meters (10 sq ft). That would be a little too big? 

I feel stupid but I didn't actually measure its depth ...... I would guess 2-3 cm

 

On 12/05/2024 at 17:00, Tony Brooks said:

I think that I would loosen the hose clip where the braided "overflow" hose and take the copper pipe out of the hose. Then when you fill air has a means of escape. Then run the engine at fast idle until the manifold starts to get warm. That means the thermostat has opened so any air trapped in the engine or pipe work should be in the manifold. Stop the engine and fill the system via your normal filler until coolant flows out of the hose. Reconnect and it should be bled as long as there are no bows in the pipes that can trap air. Personally, I would investigate moving the vent pipe to high up on the main filler pipe so any trapped air has an easy path out of the main circuit.

 

 

- The hose you mention is, I feel, an overflow of some kind. Let me explain;

When I flushed the system with a garden hose in the filler cap, water came out of where the thermostat should go + the exhaust manifold (through the hole connecting it to the thermostat, not the smaller hole on top connected to said pipe)

But there was nothing coming out of this copper pipe with braided hose, nothing at all

So my conclusion would be that is the overflow? Allowing for coolant to get back to the filling cap when it heats too much? 

Also, there was a lot of gunk in the thermostat housing and surroundings. That flush was certainly not too much, glad I got to do it anyway

Any idea how I should proceed to bleed when refilling, in this case?

 

- No presence of a valve, pressure cap, anything like that indeed. So the system is definetely not under pressure

 

I can't express my gratitude enough for the help I got here! I'm happy I can understand the way my system works way better now. So thanks again guys!

[Tracy D'arth]

Ensure that the small tube is not blocked as it will serve as an air vent to bleed air from the manifold.

[Tony Brooks]

 

1. My calculation was that you need about 0.8 sq m of sin tank base surface area, so yours is fine as far as surface area goes. To my mind 3 cm depth is not ideal, especially on a horizontal tank on the base of the boat because some hot water can stay at the top of the tank and not get cooled, but then your area is a bit larger than needed. I think it should be fine.

 

2. You don't need an overflow hose or pipe, but you do need a way of venting air from the top of the system, plus any coolant that needs to be vented because the coolant will expand when heated.

 

You will remember me saying that I suspected the pipe connected to the braided hose ran to close to the top of the filler pipe. Just below the deck fitting, but you told us that it ran to the skin tank. That means that when filling, air can be trapped in the copper pipe and the engine/manifold because there is no way for it to get out. Unless I can see photos of exactly where that pipe runs, I still think you are incorrect. That manifold, as the highest point in the system, MUST have a means of venting air when filling.

 

2. When did you expect water to come out of the hose when you were flushing the system. Water finds its own level, and the thermostat hole in the head is lower than the top of the manifold. Unless you blocked the thermostat hole water would be very unlikely to come out of that hose. Even if you did block the hole, the hole and hose on the manifold that connected it to the thermostat housing would still be lower than that braided hose, so all the water would flow back towards the thermostat housing, not out of the little hose.

 

To reiterate - I am sure that small hose and the copper pipe form a breather and expansion pipe and normally nothing will flow through it except:

 

a. Air while filling the system

 

b. The coolant as it expands when the engine heats up the FIRST run after filling. At that time, the surplus coolant will vent from the hole in the filler cap. Once the system has vented the excess coolant, the level in the filler pipe should be the correct cold level - and it will be some way down the pipe. Take note of this level and that will be your topping up level.

 

3. To bleed the system, disconnect the small hose from the copper pipe and fill slowly until coolant appears at the top of the hose. Then reconnect.

 

Then ensure that copper pipe does run to high up on the filler pipe. As long as it does, then filling slowly should automatically vet the system. No valves required as long as there are no bows in pipes that can trap air.

 

5 minutes ago, Tracy D'arth said:

Ensure that the small tube is not blocked as it will serve as an air vent to bleed air from the manifold.

 

I agree with you, but not if, as the OP claimed, it runs to the skin tank. It will only do that if it vents over the side, into the bilge, or into the top of the filler tube

[Amulet]

Okay let me get this straight immediately 😅:

 

Of course I was wrong. The copper pipe does run to the top of the filling cap, not to the skin tank.

 

I guess I didn't yet understand fully what the skin tank was when I said that, my bad.

 

PLUS I also understood the bleeding part the other way around... Anyway all clear now 😅 I guess I relied too much on what I THOUGHT I understood when reading, not enough on logic and... gravity indeed 🤦‍♂️

 

I guess I'll be able to put everything back together as intended in the next few days, all thanks to this thread! 

I'll also "measure" how much I put back into the system just for the sake of knowing

You can expect a debrief from me when it is done, if it may ever help anyone else

 

I'll drink one on your guys' health when cruising next time!!

[Tony Brooks]

Pleased we got that sorted, it should be a reliable system that is east to refill as long as you take your time, it should self bleed and hopefully the thermostat will cure it. If you have a calorifier for hot water, beware, it will be about 10 degrees hotter than it was.

[Amulet]

So here I am, a few months later. 

Been able to use the boat for a week and actually even brought it closer to where I live. 

 

I changed the thermostat, flushed through the whole cooling system and filled it back up with cooling fluid. I didn't have time to try it out on the long run until last week though.

 

On the first day of cruising, I used the engine for 2 hours on 1200 rpm. It overheated and we let it cool down for 1-2h; decided we would only use it in idle from there on. And let it cool down for at least an hour after every MAX 2 hours of navigating (we did a bit more a few times, no choice)

So we managed to cruise the whole week at this pace without having the engine turn off once. 

 

At cold start or after 1-2 hours of cooling it, it doesn't (or barely) smokes. It starts smoking more and more after 1-2 hours of navigating. Lightly blue-ish smoke, but actually more white then blue.

Clearly we are consuming oil as well.
The thickening smoke was a sign for us to start looking for a mooring spot to let it cool off. 

I feel like the cooling fluid is running correctly now with the new stat but it's difficult to confirm that part. 

 

I had a mecanic look at it and he would like to re-do the head gasket and change the water pump + clean and flush the whole system (again). Change the hoses, maybe.

I feel that won't do it any harm. Although I would love to get rid of this overheating problem for sure before I overheat and ruin my newly installed gasket, by then.

I feel like he should also check the pistons and segments? Or am I wrong?

 

Any other input?

 

 

 

 

[Tony Brooks]

I don't think that your skin tank dimensions are correct. I think it is far too small for the engine. The depth of the tank can be ignored, only the surface area in contact with the water counts. In fact, the deeper the tank, the less effective it is likely to be. I think that you have mixed mm with cm, but the numbers look ok.

 

Looking at the photo, I estimate the tank size is about 5 to 6 inches wide by about 4 to 5 ft long, so 0.5 ft x 5ft = an area of 2.5 sq feet, not the 10 you posted. If my estimation of size is anything like correct, no wonder it overheats.

 

75 cm is over 2 feet, and your skin tank looks more like 75mm. The 125cm length looks about correct. That gives a tank area of just shy of 10 sq cm or just over 1 sq foot. Please double check my working.

 

Please remeasure that skin tank, length & breadth, ignore the depth. Also be aware that baseplate mounted skin tanks, especially ones as thick as yours looks, are less efficient than vertical ones because hot water rise to the top, away from the cool bottom.

Edited July 24 by Tony Brooks

[system 4-50]

What %age antifreeze are you using?

[Amulet]

Yes, your skin tank theory is what keeps sticking in my head. That's why I am hesitating on getting the head rebuilt before making sure what the cooling issue is.

 

Not getting the gasket rebuilt and navigating like this for a while might damage the engine even more, I feel?

 

I'm pretty sure about the measurements 😉 125x75 cm (you can see a big part of it on the picture below, left side under that vent tube. On top you don't see where it ends. It ends where that brown tissue thing starts)

I measured it twice last time but will remeasure tomorrow on site and maybe get a better picture. Not easy getting everything in frame down there.

 

System 4-50: your answer came in when I was going to post the above! I did 100% antifreeze, no water at all.

 

 

 

[Tony Brooks]

2 minutes ago, Amulet said:

Yes, your skin tank theory is what keeps sticking in my head. That's why I am hesitating on getting the head rebuilt before making sure what the cooling issue is.

 

Not getting the gasket rebuilt and navigating like this for a while might damage the engine even more, I feel?

 

I'm pretty sure about the measurements 😉 125x75 cm (you can see a big part of it on the picture below, left side under that vent tube. On top you don't see where it ends. It ends where that brown tissue thing starts)

I measured it twice last time but will remeasure tomorrow on site and maybe get a better picture. Not easy getting everything in frame down there.

 

System 4-50: your answer came in when I was going to post the above! I did 100% antifreeze, no water at all.

 

 

 

 

That is not how wide it looks in an earlier photo showing the front of the engine, so it is probably OK then.

 

Just a thought, are you sure the hull bottom does form the bottom of the tank, and the tank is not just siting on the baseplate.

[Amulet]

 

4 minutes ago, Tony Brooks said:

 

That is not how wide it looks in an earlier photo showing the front of the engine, so it is probably OK then.
 

Just a thought, are you sure the hull bottom does form the bottom of the tank, and the tank is not just siting on the baseplate.

 

 

Yes I had another look at earlier pics and there is one where it looks way less wide then it is, indeed.

Not sure about that last part Tony... I am waiting for my turn at pulling the boat out of the water in the ship yard. 

I also suspected I could find a few surprises or answers down there. For now it's a fog of war

 

I just recalled something after system 4-50's question.

I used cooling fluid, as mentioned before.

Seemed logic to me as I am used to bikes and some car engines. 

If I remember correctly, cooling fluid is just antifreeze pre-mixed with water.

So maybe the one I used isn't good? I read something about at least 50% antifreeze if I recall?

Did I make an oopsie there?? I'll check it's composition at the boat tomorrow. 

[Tony Brooks]

6 minutes ago, Amulet said:

 

 

Yes I had another look at earlier pics and there is one where it looks way less wide then it is, indeed.

Not sure about that last part Tony... I am waiting for my turn at pulling the boat out of the water in the ship yard. 

I also suspected I could find a few surprises or answers down there. For now it's a fog of war

 

I just recalled something after system 4-50's question.

I used cooling fluid, as mentioned before.

Seemed logic to me as I am used to bikes and some car engines. 

If I remember correctly, cooling fluid is just antifreeze pre-mixed with water.

So maybe the one I used isn't good? I read something about at least 50% antifreeze if I recall?

Did I make an oopsie there?? I'll check it's composition at the boat tomorrow. 

 

Antifreeze has a lower specific heat capacity than water, so pure antifreeze carries less heat away from the engine than pure water. This is why the typical dilution rate is around 30% with an absolute maximum of 50%. Using more than a 50% antifreeze mixture can cause overheating,  especially with systems that are not really up to the job they are expected to do for some reason.

 

There are some factory/laboratory produced liquids that have a higher specific heat, and they may well be sold as "cooling fluid" at a suitable price hike, but then maybe pre-mixed antifreeze and distilled water is described in the same way. Without a name so its specifications can be checked, nothing more can be said.

[Troyboy]

I have a narrowboat from the 80's with a BMC 1.5 diesel engine and had similar overheating problems to yourself . It was cured by doing away with the skin cooling tank and having boxed section pipes welded along the swim . This was carried out by Charlie Fox [who is sadly no longer with us ] at March . The boats he built were all cooled this way and using this modification  means the system now runs unpressurised . I've had no overheating problems since 

[Amulet]

15 minutes ago, Tony Brooks said:

 

Antifreeze has a lower specific heat capacity than water, so pure antifreeze carries less heat away from the engine than pure water. This is why the typical dilution rate is around 30% with an absolute maximum of 50%. Using more than a 50% antifreeze mixture can cause overheating,  especially with systems that are not really up to the job they are expected to do for some reason.

 

There are some factory/laboratory produced liquids that have a higher specific heat, and they may well be sold as "cooling fluid" at a suitable price hike, but then maybe pre-mixed antifreeze and distilled water is described in the same way. Without a name so its specifications can be checked, nothing more can be said.

 

Thanks for the clarification, again!!

I'll have a look at the type of liquid I used, tomorrow.

 

13 minutes ago, Troyboy said:

I have a narrowboat from the 80's with a BMC 1.5 diesel engine and had similar overheating problems to yourself . It was cured by doing away with the skin cooling tank and having boxed section pipes welded along the swim . This was carried out by Charlie Fox [who is sadly no longer with us ] at March . The boats he built were all cooled this way and using this modification  means the system now runs unpressurised . I've had no overheating problems since 

 

Thanks for the input. I could resort to having these kind of mods at some point... don't even know what is possible and who could do that in Belgium.