Air in coolant system

[Christina732]

Hello all, I would really appreciate some guidance. 

 

Last weekend I emptied the coolant on my BMC 1.8 and refilled with fresh antifreeze solution. I bled the main tank and ran the engine for a while with cap off. 

 

But when cruising the engine started to overheat after 20-30 mins and after a short break and weed hatch check it happened again the calorifier also hadn't seemed to make hot water so I fear there is air in the system. 

 

I have tried massaging the (fairly firm) hoses while the engine runs and leaving it to run capless a bit longer but this doesn't seem to have rectified things.  

 

One of the hoses did seem higher than the header tank so I've pushed that lower and run engine and there is a kind of u-shaped pipe that could be holding air?

 

Any advice very gratefully received!

Christina 

 

 

[Tony Brooks]

Your first photo shows TWO oil coolers, with that gearbox there is normally just one, so what is the other one for? I suspect it may be an engine oil cooler that is not normally needed on an inland boat and some have been shown to cause problems with the oil.

 

At least the pipe inverted U shaped pipe joining them looks large enough to cope with the flow on a tank or keel cooled boat, but the hoses connected to the left of the oil coolers look far too small, they look like pipes used on a raw water cooling system so either direct raw water cooled (which your exhaust manifold suggest it is not) or heat exchanger cooled.

 

If it is heat exchanger (indirect raw water cooled) then there is another water pump and the raw water system to consider. You can get some very odd bodges on older boats, so nothing is absolutely certain.

 

That inverted U pipe between the oil coolers seems ideal to cause an air lock on a keel or tank cooled system, although a raw water pump would probably have no problem clearing it.

 

The hose looped across the top of the engine is feeding the calorifier so if that has air in it the calorifier will not heat, but it should not affect the rest of the cooling system.

 

You say that you bled the "main tank" can you confirm that is, in fact, the skin tank?

 

Some history please, how long have you had the boat, did this ever happen before?

 

I am afraid this looks like bit of a bodge type installation, not only the twin oil coolers, but also the electric fuel pump secured by a black plastic zip tie, I would not be surprised if that was failed by a BSS examiner.

 

 

Back from breakfast now.

 

To try to bleed that hose across the top of the engine, try the following.

 

Locate where the calorifier return hose joins the main return into the engine water pump, probably below the manifold towards the front on the port side.

 

Free the joint, but do not yet remove it. Take off the coolant filler pressure cap.

 

Mix up a watering can of antifreeze mixture and give it to an assistant standing above the coolant filler.

 

Run the engine at about 1500 RPM and pull the calorifier hose off that connection, very quickly putting your thumb over the engine side of the connection to stop coolant spewing from the engine itself.

 

Water will flow from the calorifier pipe, so the assistant needs to keep the filler topped up. After a short while, you will get slugs of air out within the water. Keep going until no more air slugs comes out, then quickly replace the hose and tighten the connection.

 

I doubt this will affect the overheating, and if there is air/gas elsewhere in the system it might move into the calorifier circuit and stop it heating again.

 

Also be aware that the oil coolers can clog the coolant flow under the rubber caps. If this is tank cooled, then if the draining shifted any rust this might block there and restrict the flow even more than the small hoses. If a hose has started to shed its inner lining, then that could also cause a blockage.

 

Can you draw a diagram of the cooling hoses showing where and what they run to and the rough hose size?

 

 

[Christina732]

Hi Tony, 

 

That's incredibly kind and helpful thank you for such a detailed reply. 

 

I will go to the boat and draw up the pipe diagram shortly but to answer your questions in the mean time. 

 

-I will check what the 2nd oil cooler is connected to. I did think it was odd I'd never seen another engine with 2!

 

-The engine used to be raw water cooled but at some point has been converted (perhaps not very optimally!) to a closed system (sorry not sure if that's the right term) at some point before I owned the boat. 

 

- Yes it was the skin tank I bled - sorry I'm a bit of a novice!

 

- I have owned the boat for a couple of years but this is the first time I have completely changed the coolant so unsure if this is a repeat issue but have had some sporadic issues with overheating at various points so perhaps the system explains that!

 

-The cable ties were in fact my bodge after the fuel pump bracket sheared off recently but will make sure to find a better solution (especially as my bss is coming up!) So thank you for pointing that out! 

 

I will bleed the top hose as suggested today thank you for explaining that so clearly. 

 

In regards to the other potential issues, would replacing the rubber end caps on the oil coolers and replacing the thin hoses with larger ones be a good idea? Or would removing the coolant and flushing the system be likely to help in the meantime?

 

Is the U shaped pipe likely to serve an important purpose or could I potentially remove and bridge with straight pipe?

 

Thank you so so much for the guidance, so appreciated. I will report back! 

[Tony Brooks]

56 minutes ago, Christina732 said:

Hi Tony, 

 

That's incredibly kind and helpful thank you for such a detailed reply. 

 

I will go to the boat and draw up the pipe diagram shortly but to answer your questions in the mean time. 

 

-I will check what the 2nd oil cooler is connected to. I did think it was odd I'd never seen another engine with 2!

 

-The engine used to be raw water cooled but at some point has been converted (perhaps not very optimally!) to a closed system (sorry not sure if that's the right term) at some point before I owned the boat. 

 

- Yes it was the skin tank I bled - sorry I'm a bit of a novice!

 

- I have owned the boat for a couple of years but this is the first time I have completely changed the coolant so unsure if this is a repeat issue but have had some sporadic issues with overheating at various points so perhaps the system explains that!

 

-The cable ties were in fact my bodge after the fuel pump bracket sheared off recently but will make sure to find a better solution (especially as my bss is coming up!) So thank you for pointing that out! 

 

I will bleed the top hose as suggested today thank you for explaining that so clearly. 

 

In regards to the other potential issues, would replacing the rubber end caps on the oil coolers and replacing the thin hoses with larger ones be a good idea? Or would removing the coolant and flushing the system be likely to help in the meantime?

 

Is the U shaped pipe likely to serve an important purpose or could I potentially remove and bridge with straight pipe?

 

Thank you so so much for the guidance, so appreciated. I will report back! 

 

Many thanks for the prompt reply.

 

As, I suspected, this was once a heat exchanger (indirect raw water) cooled engine, probably from a seagoing boat. The upper oil cooler looks like the engine cooler to me.

 

As long as this is an inland boat, I think that you could simply disconnect the water hoses from the engine oil cooler and take that U pipe out of the system. Transfer the small hose from the engine oil cooler to the other end of the gearbox oil cooler but turn the right-angled rubber end cap through 90 degrees so the hose lays more horizontal, you will probably have to extend the hose.

 

That will remove the U bend from the cooling system but will not deal with what I think are very undersized hoses for a tank cooled system. If it worked properly before the antifreeze change, than it will hopefully work well enough again, so you can see if that cures it. If it does, then you can probably leave it a sit is FOR CANAL USE ONLY.

 

If you might go onto rivers I would get a pair of new end caps for the gearbox oil cooler, I think ASAP supplies sell them and probably Calcutt Boats that have larger inlet ports so you can fit larger hoses from the skin tank to the cooler and from the cooler to the engine water pump. I would want at least 1" i.d. and 1.25" is better.

 

It would also be worth taking the rubber end cap off one end of the exhaust manifold to check the heat exchanger core has been removed. If it has been left in then that too will restrict the flow. With the cap off you should just see a big hole, not a disk with a load of little holes in it.

 

FWIW, there are two forms of raw water cooling and people don't seem to understand that and confuse people by not properly identifying their system. In your case, the engine was never direct raw water cooled because the manifold and thermostat housing are wrong, it was a heat exchanger system with two water circuits. Basically the conversion for tank cooling should have been to discard all the raw water parts and hoses, plus the heat exchanger core, and fit large bore hoses to the skin tank. Whoever converted yours forgot to change to large bore hoses.

 

[Christina732]

Ah brilliant that's extremely helpful Tony thank you. Almost at the boat so I will give bleeding the top hose and redirecting the cooler hose a go. 

 

All seemed to work well before my fiddling so hopefully that will be enough to rectify things but switching to larger hoses and checking for remaining heat exchanger core does sound like a very good idea as I have always had problems with overheating so that would be amazing if that would finally sort those issues!! Thank you so much for the detailed guidance for those bits too. 

 

Also that makes sense with the raw systems. Thank you for bearing with through my somewhat confused descriptions!

 

 

Wish me luck! Will let you know how it goes!

And here is the diagram my lovely OH has made in the interim!

[Tony Brooks]

3 minutes ago, Christina732 said:

Thank you for bearing with through my somewhat confused descriptions!

 

I wish more did as good a job of describing the fault and showing what they have as you did, and answered the questions asked promptly and fully.

 

If the previous overheating happened when you were driving the engine harder than normal, then the hoses could well be the problem. The engine water pump is a centrifugal one and if the outlet flow is restricted then they just spin round and pump less water. That means less hot water is pumped to the skin tank, so less cooling takes place

10 minutes ago, Christina732 said:

Ah brilliant that's extremely helpful Tony thank you. Almost at the boat so I will give bleeding the top hose and redirecting the cooler hose a go. 

 

All seemed to work well before my fiddling so hopefully that will be enough to rectify things but switching to larger hoses and checking for remaining heat exchanger core does sound like a very good idea as I have always had problems with overheating so that would be amazing if that would finally sort those issues!! Thank you so much for the detailed guidance for those bits too. 

 

Also that makes sense with the raw systems. Thank you for bearing with through my somewhat confused descriptions!

 

 

Wish me luck! Will let you know how it goes!

And here is the diagram my lovely OH has made in the interim!

 

Thanks, that all looks typical, apart from the hose size, so it should be OK for low powers once any airlocks have gone.

 

If you want a quick "bodge" to ensure no air is trapped in that inverted U pipe, then get a piece of rubber sheet and a Jubilee 9worm drive) hose clip that fits around the pipe and rubber sheet. Drill a very small hole right in the top of the U pipe to let any air out and once just coolant is flowing out, seal it with the rubber sheet and hose clip. If that works, then you could, in the future, get a bleed point brazed or soldered onto the U pipe.

[beerbeerbeerbeerbeer]

I’ve two oil coolers on my 1800,

exactly same as yours ,

never had a problem over 10 years,

I don’t believe it’s a bodge, 

don’t worry

[Tony Brooks]

4 minutes ago, beerbeerbeerbeerbeer said:

I’ve two oil coolers on my 1800,

exactly same as yours ,

never had a problem over 10 years,

I don’t believe it’s a bodge, 

don’t worry

 

Is your indirect raw water cooled? You won't get problems with that. Otherwise, can you explain why all the various marinisers I know use large bore hoses for the skin tank circuit.

 

Believe what you want, but those thin hoses on the skin tank circuit are a bodge or all the other mairnisers are wrong and wasting money on oversized hoses.

[Tracy D'arth]

I plumb skin tanks in 28mm copper with corresponding hose sizes, never a problem with BMC 1.5D and 1.8D engines. 2.2D may need a bit more if worked hard offshore but not for canal use.

[Tony Brooks]

21 minutes ago, Tracy D'arth said:

I plumb skin tanks in 28mm copper with corresponding hose sizes, never a problem with BMC 1.5D and 1.8D engines. 2.2D may need a bit more if worked hard offshore but not for canal use.

 

I agree, but look at the size of the hoses running to and from the cooler pair. looks like 5/8"  heater hose to me, certainly nowhere near 28mm.

[beerbeerbeerbeerbeer]

1 hour ago, Tony Brooks said:

 

Is your indirect raw water cooled? You won't get problems with that. Otherwise, can you explain why all the various marinisers I know use large bore hoses for the skin tank circuit.

 

Believe what you want, but those thin hoses on the skin tank circuit are a bodge or all the other mairnisers are wrong and wasting money on oversized hoses.

no I can’t explain why two coolers are unusual enough to quickly conclude a bodge job,

and I’m tired of arguing with folk,

I’ll politely nod and agree,

 

[Christina732]

So we went with the bodge for today and managed to drill a hole in the u shaped pipe and clip some spare hose over it once the air cleared. 

 

The bleeding from the calorifier produced a very meagre flow even with good revs which made us doubt we had the correct pipe, checked the other and definitely had it right the first time. Decided to have a test before attempting to bleed further and the engine was not overheating anymore whilst out of gear with some revs and produced some warm water!! 

 

The acid test will be a short move this weekend so fingers crossed but looking like it's enough to get me from A to B while I order some larger hose to hopefully improve the flow overall and have a much happier engine. 

 

And yes you're right the overheating tends to happen in higher revs/very hot days/if a piece of weed even thinks about my propshaft so hopefully that will improve things. 

 

Thank you so much Tony for your time and very well explained steps I would have been in quite a pickle otherwise! Hugely appreciate your efforts and very relieved!!!

[Tony Brooks]

1 hour ago, beerbeerbeerbeerbeer said:

no I can’t explain why two coolers are unusual enough to quickly conclude a bodge job,

and I’m tired of arguing with folk,

I’ll politely nod and agree,

 

 

It is horses for courses, and I never said the two coolers made it a bodge job. I said that I think the small hoses indicated it was. I also said that the engine probably came out of a sea boat, where there is often a need to run at close to maximum revs and power for long periods. Under those conditions with no airflow past the sump, as you get in vehicles, the oil would be likely to overheat, and as a large proportion of piston cooling is done by the oil that is likely to lead to damage, so an oil cooler is fitted. On an inland boat where powers are more limited and stops for locks fairly frequent, the use of an engine oil cooler can over cool the oil, to such an extent it never gets hot enough to evaporate condensation from piston blow by from the oil. The result is a build up of "water" in the oil that then emulsifies so it thickens. This was so bad on the Perkins 4-i07s and 4-108s where Perkins demanded an engine oil cooler, it was occasionally necessary to drop the sump to get jelly like oil out.

 

In my view when converting an indirect raw water cooled engine for skin tank or keel cooler use any engine oil cooler is better disconnected AND the main coolant pipes changed for the same size as used between the manifold and thermostat housing, and manifold to water pump. Nether was done in this case as far as I can see.

 

The reason you find people argue with you is that have a bit of a habit of posting questionable advice that as far as I can see you do not have the theory or practical experience to give. I note in this case you have not confirmed exactly what type of cooling system you have because a Jabsco type raw water is probably powerful enough to purge any air trapped in the inverted up, so no problem.  As I explained, the engine water pump is a totally different type and an air bubble in that bend is very likely to prevent circulation. You will note that the OP  said "So we went with the bodge for today and managed to drill a hole in the u shaped pipe and clip some spare hose over it once the air cleared" so air was trapped in the bend.

 

The OP also says they got some warm water and the engine did not overheat while revving in neutral. I rather think that tends to prove my point that the conversion for tank cooling was a bodge.

 

It gives me no pleasure to call out potentially misleading advice or to be proved correct, but it is necessary because it seems many members give advice from the best of motives, but base it on very limited experience, that can be misleading.

Edited November 25, 2023 by Tony Brooks

[Christina732]

Interestingly when changing the oil with a very experienced engineer we did really struggle to suck the old oil out and this took us a great deal of time due to the viscosity which makes a lot more sense now!

[beerbeerbeerbeerbeer]

With all respect Tony,

I have the same set up as the OP,

pipes going to and from a skin tank,

pipes that look the same size and I’ve never had the trouble you’ve described,

and never had trouble bleeding the system.

 

I do not have a calorifier and would not know what one looked like,

 

I wonder if you’ve over complicated the issue for the OP?

Probably not really necessary to drill a hole and fit a draining tap,

or perhaps go to the expense of bigger pipes just yet,
they won’t be cheap,

 

Before spending a lot of money on new pipes I’d rule out the much easier to solve causes of possible over heating,

Or perhaps the OP has exhausted those possibilities? 🤷‍♀️

but as you say...what would I know,

 

 

[Tony Brooks]

8 hours ago, Christina732 said:

Interestingly when changing the oil with a very experienced engineer we did really struggle to suck the old oil out and this took us a great deal of time due to the viscosity which makes a lot more sense now!

 

I think that simply preventing coolant flow through the engine oil cooler will be enough to minimise that happening again.

[beerbeerbeerbeerbeer]

OP,

for what it’s worth and simply for comparison, I’m not advising anything,

 

just measured my pipes with callipers,

the gear box oil cooler is plumbed in with 28mm copper pipes, and hose to fit

the engine oil cooler is plumbed in with 30mm copper pipes, and hose to fit,

so far in 11 years, (touch wood), they’ve not bought me any problems,

good luck with whatever you do,

will be interesting to know how you get on

 

 

 

[Tony Brooks]

There you go, so not "exactly the same as yours" then. The hose/pipe size feeding and returning the coolant are larger on yours, exactly what I was suggesting to the OP.

 

What is this "I don’t believe it’s a bodge, don’t worry" if not advice "not to worry".

 

Don't bother to reply, but just take more care with details next time you use what looks like limited experience to advise others.

[beerbeerbeerbeerbeer]

Wow,

it’s not me that’s never seen an oil cooler on a canal boat engine before!

and using an engine oil cooler is really what I was referring to when saying don’t worry

 

 

7 hours ago, Tony Brooks said:

I think that simply preventing coolant flow through the engine oil cooler will be enough to minimise that happening again.

Explain this please?

Because I don’t understand and do want to learn.
Seems you’re suggesting her pipes are two small and should be exchanged for larger, yet advise restricting flow through the engine cooler, seems a contradiction.

 

I think you said somewhere having an engine cooler like in the photo with a water jacket isn’t a good idea because the oil never gets up to temperature? So how will the oil get up to temp if the pipes are widened and deliver more water?

I don’t get it. I’m missing the obvious, obviously. 

 

 

Edited November 26, 2023 by beerbeerbeerbeerbeer

[Tony Brooks]

Just now, beerbeerbeerbeerbeer said:

Wow,

it’s not me that’s never seen an oil cooler on a canal boat engine before!

and using an engine oil cooler is really what I was referring to when saying don’t worry

 

 

Explain this please?

Because I don’t understand and do want to learn.
Seems you’re suggesting her pipes are two small and should be exchanged for larger, yet advise restricting flow through the engine cooler.

 

 

More than happy to explain. There are two different "problems" here. One is the undersized pipes. I don't think that is now in dispute.

 

The second is the POTENTIAL for engine oil coolers on any boats that operates for most of the time on very restricted revs and power to over cool the oil so condensation from piston blow by does not evaporate away. Note the word potential, and also note that the OP said they did have problems draining very viscous "oil" from the sump. That is exactly what I explained could happen with an engine oil cooler on an inland boat.

 

Whether it does happen or not depends upon how the individual boater uses their engine, so running the engine for hours on idle in neutral to get the batteries fully charged is likely to make it the likelihood of emulsified and thickened oil greater, while boating on wider and deeper canals at higher speeds than narrow canals allow, or making excess wash on narrow canals, is likely to make emulsification less likely. also, if you are a stickler for oil change intervals the oil will still emulsify, but not as badly as if you extended the intervals to suit your agenda.

 

I do not believe that the two oil coolers in parallel is a problem cooling wise as long as the pipe size is adequate, but in this case I would prefer the inverted U tube to be horizontal, so there was less likelihood of trapping air (not so applicable to a system using a Jabsco type pump). Knowing the propensity for some inland engines to emulsify their oil I suggested that the engine oil cooler be disconnected from the cooling system so the oil passing through it was not cooled. This has an advantage of simplifying the coolant pipework and bosting the oil temperature with the minimum of work. Also, if it did turn out that oil cooling was necessary, reconnect the coolant pipes is a relatively simple matter.

 

 

 

[Christina732]

Gave the engine a good test on a cruise today and it was faultless! Maybe even ran very slightly cooler than usual, maybe just the cold weather but maybe a little air has been trapped for years?!

 

Very happy and sorted for now but definitely planning to enlarge the hoses in the spring to keep temps and oil viscosity happy

[Tony Brooks]

Many thanks for the feedback. Pleased, it seems to be fixed.