Layer of blacking on skin tank too thick?

[Richard T]

We also have a 62ft Colecraft from 1988 fitted with a Calcutt BMC 1.8. I've not measured the skin tank but it appears to be just about big enough. Water temp is somewhere between 80 & 90degrees dependent on engine revs. We boat a lot on the Soar and Trent and know where we the flow is faster so tend to make sure the temp is down before entering one of these sections. From memory a BMC 1.8 is around 33hp but doubt that ours after nearly 10k hours is capable of delivering this. Will measure skin tank tomorrow.

[alan_fincher]

 

I've measured the skin tank and it is about 46 inches from front to back and 20 inches high. I'm not sure of the width but it protrudes inwards by about 3/4 inch.

 

That sounds OK for any normal canal use, but maybe marginal for working hard on rivers. I doubt that skin tank size is your main problem.

 

If it protrudes inwards by the amount you say this is good, as a "thin" skin tank makes it far harder for the water to pass through it without getting near the cooled side. Badly designed ones are often 3 or 4 inches "thick", which means that water can travel up the side away from the canal , and hence avoid being cooled. As an aside, it also means your cooling circuit contains 3 or 4 ties more coolant than ideal, increasing the likelihood of there being insufficient room for expansion without overflowing. (You would also be spending far more on antifreeze, and have far more to dispose of if you change it.)

From memory a BMC 1.8 is around 33hp but doubt that ours after nearly 10k hours is capable of delivering this.

 

Different marinisers quote different numbers, but for the 1.8, it is invariably somewhere between 30HP and 38HP.

[blackrose]

We also have a 62ft Colecraft from 1988 fitted with a Calcutt BMC 1.8. I've not measured the skin tank but it appears to be just about big enough. Water temp is somewhere between 80 & 90degrees dependent on engine revs. We boat a lot on the Soar and Trent and know where we the flow is faster so tend to make sure the temp is down before entering one of these sections.

I don't really understand this? Your cooling system should be capable of maintaining a sufficiently low temperature over a prolonged period of high revs. A test would be at least 90 mins at full revs without overheating.

 

If you have to make sure the engine temp is low before using full revs it suggests the cooling system isn't adequate.

Edited August 10, 2015 by blackrose

[Richard T]

Our cooling system may be inadequate in certain circumstances but for the majority of time it is more than adequate. The trick is to understand when it will be under pressure and to boat accordingly. If in doubt we do not move until river levels have gone down. I cannot think of a situation where I would use full power for more than 15 minutes. The gut at cranfleet takes about 7or8 minutes to get through when the Trent is up a bit and less at normal ones. If we were going to do major river trips against current or tide we would consider getting a further cooling system fitted.

Edited August 10, 2015 by Richard T

[alan_fincher]

 

 

Are these builders known for not building baffles into the skin tanks? I happen to have a Mike Heywood and have what you might call a quadrant fitted to one side of the engine bay floor. The boat has a BMC 1.5 and I haven't noticed any problems with overheating through insufficient skin tank surface area. But, I've often thought it might not be good enough if I had to give the engine some welly against the current of a river.

 

My understanding is that build wise Mike Heywood and Evans & Son are effectively the same thing.

 

After he ceased reading as Mike Heywood, he then built as Evans.

 

Our Evans & Son boat had about the worst imaginable skin tank, being only 2 feet in each direction, (4 sq ft), but 4" thick and unbaffled. How the previous owner of 10 years had put up with it I have no idea, but it certainly wasn't adequate even for canal use. We had a baffled tank of more like 10 sq feet built on the outside of the swim, (about an inch thick), and this totally transformed the boat. You could thrash it hard, and temperture never then rose above thermostat temperature, even if you pushed on hard for hours.

 

I can't imagine this was the only boat Mike Heywood got so severely wrong when building a skin tank!

[Allan(nb Albert)]

We also have a 62ft Colecraft from 1988 fitted with a Calcutt BMC 1.8. I've not measured the skin tank but it appears to be just about big enough. Water temp is somewhere between 80 & 90degrees dependent on engine revs. We boat a lot on the Soar and Trent and know where we the flow is faster so tend to make sure the temp is down before entering one of these sections. From memory a BMC 1.8 is around 33hp but doubt that ours after nearly 10k hours is capable of delivering this. Will measure skin tank tomorrow.

From memory, Calcutt recommend a skin tank of at least 10 sq ft for their 1.8 BMC engines and also give advice on the use of saddle tanks (maybe this is because it is difficult to get 10 sq ft on one side of a swim!).

 

As I said earlier, my Thorneycroft 108 manual gives 90 degrees as the normal operating temperature with an 82 degree thermostat so 80-90 would seem ok.

 

[comfortably numb]

I'm still trying the things you very helpful folk on here have suggested, the next one is replacing the water pump in the coming week.

 

I've thought of something else but even allowing for my dumbness with anything mechanical I wouldn't have thought this would have caused the overheating but thought I'd mention it just in case. About 18 months ago (and I think was about the time I began to have the problem but this could be coincidence), a bolt came loose in the gearbox (caused by a too low tick-over and knackered engine mountings).

 

Thankfully I was right by the boat place in Stone. They checked it and found that the bolt rattling about in the gearbox had made small pock marks all over the drive plate and that I'd been lucky it hadn't cracked. They replaced the engine mountings and adjusted the tick-over.

 

Their opinion was that it would be okay with the pock marks and that I wouldn't need a new drive plate, and since then I haven't noticed any changes to the performance of the engine or gearbox.

 

So could this be relevant to my overheating problems?

[Higgs]

 

My understanding is that build wise Mike Heywood and Evans & Son are effectively the same thing.

 

After he ceased reading as Mike Heywood, he then built as Evans.

 

Our Evans & Son boat had about the worst imaginable skin tank, being only 2 feet in each direction, (4 sq ft), but 4" thick and unbaffled. How the previous owner of 10 years had put up with it I have no idea, but it certainly wasn't adequate even for canal use. We had a baffled tank of more like 10 sq feet built on the outside of the swim, (about an inch thick), and this totally transformed the boat. You could thrash it hard, and temperture never then rose above thermostat temperature, even if you pushed on hard for hours.

 

I can't imagine this was the only boat Mike Heywood got so severely wrong when building a skin tank!

 

 

Thanks for the reply. My boat is 1983/4. I wouldn't bank on the cooling being good enough for rivers, but on the canal it's fine. To consider the rivers will probably require an extra skin tank.

[Midnight]

I think there is a general issue with many narrowboats having a skin tank which is too small for the engine.

 

For the first 6 years Midnight would run hot, close to the red on rivers especially going upstream. This caused the water to leak past the radiator cap and put air in the skin tank. I ended up venting the skin tank each day we cruised.

 

After I changed the leisure alternator to a Prestolite 110amp the problem became intolerable running over 90 degrees even on some canals. I met a boater at Bardney on the Witham who measured my skin tank and told me that it was far too small for the Beta 43. He said I needed at least 7 square feet. On the way back I dropped the boat off at Lee Guest's yard in Thorne he fitted a second skin tank and since then the temperature has never gone above the norm and I've never had cause to vent the skin tank again.

 

Several moorers at Ripon experienced same and some also had second skin tank fitted with same results.

[mango]

I did say 'supposedly'. We bought the 11th share in October 1999 and sold it in 2004.

The skin tanks on our current Reeves hull form the engine bed and hold something like 20 gallons of coolant.

This suggests that the skin tanks are larger than necessary. A thin skin tank with baffles will give a rapid flow of coolant against the hull and achieve more effective heat exchange. One skin tank of appropriate area may be perfectly adequate and makes the plumbing easier.

 

One problem with having a large volume of coolant is that there must be a header tank with sufficient capacity to allow for expansion.

[Theo]

 

 

I am wondering if you can check that the baffles in you skin tank are working properly. If you are able to get at the whole inside surface of the skin tank from within the boat you shoul be able to put your hand on it to check how it warms up from cold. This should allow you to see if the water is short circuiting from inlet to outlet

[Richard T]

Just for the record I've now checked the area of the skin tank on our boat it is about7 sq ft. Which is ok in most situations but marginal when running hard.

Just been looking at a boat having a new engine fitted. The original skin tank varied in thickness because the builder had not followed the curve of the swim - he'd simply welded in a flat plate so the thickness varied from 1 To 5 inches. Needless to say the boat had overheating problems!!! A new skin tank has been fitted with the engine.

Edited August 16, 2015 by Richard T

[Cheshire cat]

The OP stated that this is a problem that has come on relatively recently.If that is the case the cooling system was once fit for purpose.

 

As well as skin tank size the other important factor has got to be speed of flow. Is the hot water getting away from the engine fast enough?

 

Cold water may well becoming out of the skintank but if the flow is low it won't be doing its job.

 

I wonder if the impeller is still attached to the water pump and whether there are any partial blockages, collapsed hoses etc.

 

Things do deteriorate over time. We still have a share in a Pat Buckle boat (Steelaway). It experienced cooling problems after having the BMC replaced by a larger Nanni. Anything over 1300 rpm the temperature would rise whereas the BMC had been happy at 1800-2000.

 

The Calcutt modification was done to the skintank and temperatures stayed down at 70 no matter how hard the engine was pushed.

 

Nine years later....................

 

Last week I was faced with a temperature warning buzzer after cruising through the middle levels at 1300 rpm. Perhaps the skin tank needs bleeding. Unfortunately the original bleed screw is well rounded and really ought to be replaced.

 

I was wondering if some of that fluid used for descaling kettles would do any good prior to flushing. Has anyone tried it?

[mango]

Surely it was a typo and he meant 18" dia?

 

I'd be surprised if a Colecraft had an undersized skin tank. Stupid question, but did you bleed the tank while the engine was running? Also, might not be relevant but the cooling efficiency of antifreeze/coolant will eventually reduce. When was the last time it was changed?

How does the cooling efficiency of coolant depend on its age? It's a good idea to change antifreeze periodically to maintain corrosion protection but the efficiency of a cooling system is largely dependent on the specific heat of water.

[Cheshire cat]

Calcium deposits due to using hard water in the cooling system?

[richardf]

There are a lot of boats being overplated these days - how does this get carried out without causing cooling issues - anybody know?

[alan_fincher]

There are a lot of boats being overplated these days - how does this get carried out without causing cooling issues - anybody know?

 

It does sometimes.

 

I recall a few yeras back Nigel Carton reported on a boat that was overheating following the skin tank having been overplated.

 

IIRC the answer was to remove the overplating where it actually covered the skin tank, (the surviving steel underneath presumably then being declared "good enough" in that area?"

 

A "search" should find it.

[comfortably numb]

During the last 10 days (since the last reply to my OP), I've been mulling over what to do next. Getting all these opinions from this forum and people on our marina has been tremendous but has also increased my dilemma as to what to try next because whatever I do I have to pay somebody to do it and naturally I'm trying to avoid spending money unnecessarily.

 

A local boat mechanic is now telling me the overheating is almost certainly being caused by a faulty gearbox (PRM 160) and that my next step should be to have it replaced, which seems a drastic and very expensive option. However, could a faulty gearbox be the reason I need 2,000 RPM to maintain 4mph?

 

How likely is this to be the cause? Would I be able to tell there's a problem as I cruise along? I've not noticed anything amiss and only a couple of times in the last 70 hours of cruising has there been a sudden small dip in the revs, and each time I put this down to some debris in the water temporarily catching the propeller. The drive seems fine going forwards or going in reverse.

 

Sorry this thread of mine has gone on a bit and thanks to everybody who is trying to help me, it really is appreciated, and hopefully some of you will be kind enough to stick with me.

 

So to sum up the story so far …..

 

I have 2 main issues –

 

1. The engine (BMC 1.8) overheating (100c+) when travelling on a canal at 4mph for longer than a few minutes.

2. The revs have to be 2,000 RPM in order to travel at 4mph (assuming adequate depth of water etc).

 

The 2,000 RPM seems way too high. I haven't had the accuracy of the rev counter checked but even if it is giving a false reading it doesn't alter the fact that to maintain 4mph the engine overheats anyway.

 

Are the two issues connected perhaps?

 

Following all your helpful suggestions earlier in the thread, I have checked or done the following:

 

1. I've established that the skin tank is big enough for the engine and hull.

2. I've spoken to the chap who did the blacking in April and in his opinion it wasn't particularly thick on the skin tank part and he's certain this isn't the cause of the overheating.

3. I've re-checked to prop size and it is 17”, also checked with Colecraft that it is the one fitted when the boat was built in 1995 so it should be fit for purpose.

4. Replaced temperature gauge & sender unit.

5. Bled the skin tank when engine running.

6. Checked % of coolant in water system. New coolant was put in last year and the place that did it said they'd completely flushed out the system beforehand. I presume they weren't lying.

7. I haven't replaced the water pump but feeling the pipes and the skin tank it does seem to be pumping the water around okay.

8. Engine has always been prone to overheating on canals in the 2+ years I've had the boat but since its hard work in May on the Trent it's worse now I'm back on canals than it was beforehand.

9. At 1800 RPM (2.5 – 3mph) the engine temp is 90c. At 2,000 RPM it reaches 100c and looks like it would go above it I dared to let it. After reaching 100c it cools down to 90 – 85c within a minute or two if I reduce the revs to about 1,600 RPM. The rises & falls happen quite quickly.

10. I have about 10 shallow pock marks on the drive-plate caused 6 months after I bought the boat by a bolt inside becoming dislodged and rattling around. It happened when going through Stone on the T&M in 2013. I was virtually outside the boatyard there so gently eased to boat there to avoid major damage.

    They told me the drive-plate would be fine left as it was. I can't remember for sure, but I think my overheating problems may have started around that time but this could be coincidence of course. The high RPM's has always been the case since I bought the boat, but the overheating hasn't. So maybe this latest suggestion about it being a gearbox problem could be relevant then?

11. The water system needs topping up with approx 100ml of water about every 20 hours.

12. The engine oil rarely needs topping up, but needed so in May when I was on the rivers. Since back on the canals it's back to hardly using any oil but then I'm not working the engine as hard. I rarely do above 3mph and have only been doing the 4mph in order to test the temperature issue.

13. The engine starts pretty well from cold even in winter. It smokes a bit for the first 20 seconds or so but then is fine, even at high revs.

14. There is no sign of water in the engine oil.

15. When operating at 100c there is no visible sign of overheating (steam). When on the Trent I had the deck board up to keep an eye on it.

 

So it's what step to take next that I'm in a dilemma about. Do I get the gearbox replaced or looked at? Do I have the engine stripped down and checked? Should I replace the water pump as the next step on the basis that it's the cheapest option to try first?

 

Or on the basis that they are BMC specialists I'm considering taking the boat to Calcutt Marine and let them take a look.

 

Perhaps I should sell the boat or sink it and claim the insurance!!!

 

Any further help/advice would be very gratefully received.

[Richard T]

Ask Matty40s or RWLP or Jonathan Hewitt at Union Canal Carriers to take a look at it before going to Calcutt.

[David Mack]

Do you know for certain that the coolant is actually circulating? When the engine is running hot have you put your hand on the inside surface of the skin tank and on both hoses from the engine/gearbox to the skin tank? If the whole setup is too hot to touch then you do indeed have an overheating problem, but if any part of the cooling circuit is cold to warm to medium hot then I would say you have a circulation problem. That could be a failed pump, airlock or blockage somewhere in the pipework. If jabsco-type pumps are left unmaintained it is not unknown for one or two of the rubber vanes to break off and get sucked into the pipework and lodge at some constriction, blocking (or partially blocking) the flow.

[Rick Spleen]

I am also trying to resolve an engine overheating problem so have been following this thread with interest. My problem seems to occur intermittently. I've taken many of the steps suggested in the thread but don't know yet whether I have finally nailed the problem as the problem is intermittent. When I spoke to Beta about possible causes, one thing on their list of suggestions was whether the water filler cap needs changing. Is it the right pressure rating and/or is the spring weak after so many years in service? It seems too simple to be true but for just a few quid it can be changed and that possible cause eliminated. My engine used to run constantly at 80 degrees for 14 years, then it started edging up to 100 for no obvious reason, and now after some fettling it seems only to edge up to 90 degrees. Interestingly, I've also had gearbox problems recently but always considered the two problems were not in any way related. I've done a bit more fettling in the last day or two so will find out later this I week whether my overheating problem is cured permanently.

[alan_fincher]

So to sum up the story so far …..

 

I have 2 main issues –

 

1. The engine (BMC 1.8) overheating (100c+) when travelling on a canal at 4mph for longer than a few minutes.

2. The revs have to be 2,000 RPM in order to travel at 4mph (assuming adequate depth of water etc).

 

The 2,000 RPM seems way too high. I haven't had the accuracy of the rev counter checked but even if it is giving a false reading it doesn't alter the fact that to maintain 4mph the engine overheats anyway.

 

Are the two issues connected perhaps?

 

Do you mean a truly genuine continuous 4mph?

 

If so on what canal, and how deep at the point you are trying?

 

4mph is a maximum speed on most canals, but not all narrow boats can achieve it, and many will come nowhere close if the canal is narrow and shallow.

 

On a practical note hand held tachometers are relatively easy to come by at low cost. You could use one of these to double check the RPM the engine is at, (by measuring rotation of the crankshaft pulley), then also that that the prop-shaft is rotating at.

 

Then if (say) you have a 2:1 reduction on your gearbox, (it will be marked on it usually), but the prop-shaft is not achieving 1000 RPM, when the engine is doing 2000 RPM, you know that the box must be "slipping" in some way, and this could well be exacerbating the problem.

 

However if you establish that the speed the prop-shaft is rotating at is correct for the engine speed and the actual stated reduction ratio of your box, then I'm rather struggling to see why replacing the box is expected to cure the problem.

 

Others with more experience may wish to comment on that logic, though!

 

FWIW, the boat we recently sold, (50 foot) that had a BMC 1800 engine and a PRM box wsith a 2:1 reduction probably needed to be at over 1,500 RPM to genuinely make 4 MPH on a deepish canal, (so prop at 750 RPM). If it was shallow, then winding it up to that or above would have been counter productive, but I doubt even if run the engine at 2000 RPM for quite a while that the coolant temperature would ever have risen much above that that the thermostat opened at (82 degrees in our case).