Engine overheating

[Tracy D'arth]

3 minutes ago, AlanJ said:

 

 

When the buzzer when, the pipes to the calorifier and skin tanks were relatively cold (could easily be held)
On restarting the engine and when the buzzer did not sound, these pipes quickly got too hot to hold. 

 

It is an air lock.  Check that the pipe/s from the thermostat rise in a direction so that they self bleed any air out.

[Tony Brooks]

Just now, AlanJ said:

When the buzzer when, the pipes to the calorifier and skin tanks were relatively cold (could easily be held)
On restarting the engine and when the buzzer did not sound, these pipes quickly got too hot to hold. 

 

 

Unless the system had not run long enough to heat up, that suggest a lack of circulation. You have all but eliminated a thermostat fault, so that leaves a water pump problem, air lock, or false alarm. If the pump drive belt is in good condition, properly tensioned, ad there is no belt squeal, then that would leave the water pump itself. However, engine water pumps are a far from common failure, although it has been known for the impeller to split or fall off, but it is not a likely fault. I am sure that you have done your best to bleed the main cooling system so if you are not getting air/gas out every time you re-bleed it, it makes a head gasket failure a bit less likely. It is possible to get the calorifier circuit air locked with no airlock in the man cooling system, so that can explain the calorifier failing to heat up. That leaves a false alarm and the problem is whatever you do unless you can find someone with an IR thermometer and get the fault to appear when they are present you are going to have to buy something to complete the diagnosis.

 

 

[Psychalist]

I'd suggest airlock too, as it appears to temporarily clear and reappear next time from cold, as if the coolant circulation is blocked and then unblocked. If it was leaky head gasket, the problem would progressively get worse as more gas is pumped into the coolant circuit rather than clear itself. You could try idling from cold with the cap off and squeezing the hoses to see if any air comes out. Check the bleed and as Tony says, an infra-red thermometer is a useful option so you can check it as you go along (if that is possible).

[Tony Brooks]

A further thought:

 

I know some boats with large capacity skin tanks have problems with airlocks if they rely on a header tank that is part of the exhaust manifold. Basically the coolant expands so mush is expelled, so when it's cold the pipes have air in them that gets trapped when the coolant is topped up. The usual "cure" is to fit a remote header tank of adequate size.  I am not saying this is the problem, certainly not before an acutal overheat has been proven, but it is worth bearing it in mind.

[StephenA]

9 hours ago, Tracy D'arth said:

If the stat had failed closed the calorifier would still have been hot. Replacing the stat may have just let the  engine vent.

 

 

Are you sure? On our BMC the calorifier is on the cooling circuit - so we get the engine up full running temperature, rather than trying to bring the engine and 20+ gallons of water up to full running temperature.

[Tony Brooks]

34 minutes ago, StephenA said:

 

 

Are you sure? On our BMC the calorifier is on the cooling circuit - so we get the engine up full running temperature, rather than trying to bring the engine and 20+ gallons of water up to full running temperature.

 

Very unusual for a 1.5 and most marinised engines apart from twin thermostat one's like the Shires. It runs the risk of restricting cooling flow through the calorifier coil and associated hoses, so it's asking for overheating at high powers and speeds.

[StephenA]

23 minutes ago, Tony Brooks said:

 

Very unusual for a 1.5 and most marinised engines apart from twin thermostat one's like the Shires. It runs the risk of restricting cooling flow through the calorifier coil and associated hoses, so it's asking for overheating at high powers and speeds.

 

Even when running on tidal rivers for hours the engine never gets above the very very low 90s - which is what it did before the calorifier circuit was fitted.. On normal canal usage it sits at round about 85 once it gets up to temperature. Whole system is plumbed using 22mm or equivalent piping.

Edited August 2, 2021 by StephenA

[Tony Brooks]

1 minute ago, StephenA said:

 

Even when running on tidal rivers for hours the engine never gets above the very very low 90s - which is what it did before the calorifier circuit was fitted.. On normal canal usage it sits at round about 85 once it gets up to temperature.

 

I don't doubt what you say, but it is still unusual. In the automotive form, the cab heater takes the place of the calorifier in its normal configuration, and the heater takes heat from the engine all the time it's working. FWIW I piped my Bukh in the same way because it did not have a takeoff from the head and that was fine as well, but it was a risk until it proved itself as satisfactory.

[StephenA]

4 minutes ago, Tony Brooks said:

 

I don't doubt what you say, but it is still unusual. In the automotive form, the cab heater takes the place of the calorifier in its normal configuration, and the heater takes heat from the engine all the time it's working. FWIW I piped my Bukh in the same way because it did not have a takeoff from the head and that was fine as well, but it was a risk until it proved itself as satisfactory.

 

We did a lot of checking when it was first put in over 20 years ago. Just feels sensible to get the engine up to running temperature quickly rather than having to heat everything up, especially in winter.

[AlanJ]

Thanks for all the suggestions 

I am away from the boat now but will be back at the weekend. Will check again for air locks and check with an ir thermometer to see what is happening. 

[Tony Brooks]

I am not sure that you have made it clear is you have been or can bleed your skin tank. Most, but not all, need the air letting out of them and have screws to plugs at the top to allow this.

 

I was surprised on the courses how many boaters did not know about skin tank bleed points.

Edited August 3, 2021 by Tony Brooks

[AlanJ]

I have a big cap on the top of the skin tank and will try to loosen this. 
the feed pipe at the top of the tank has a tap in it (suggesting the top cap may be hard to remove). I will use these to bleed the skin tank. 

[Tony Brooks]

2 minutes ago, AlanJ said:

I have a big cap on the top of the skin tank and will try to loosen this. 
the feed pipe at the top of the tank has a tap in it (suggesting the top cap may be hard to remove). I will use these to bleed the skin tank. 

 

As long as the tap is more or less at the top of the skin tank level AND the hose/pipe between it and the tank slopes upwards to the tap, then the tap should bleed the tank sufficiently. If there is a gap between the top of the skin tank and inlet pipe or the pipe/hose sloped down to the tap, air is likely to be trapped in the tank. Probably not enough to cause your problems, but air expands more than water as it's heated, so the more air that is trapped in the system, the more coolant that gets expelled as the system heats up. Without seeing the setup, I can't say more.

[AlanJ]

3 minutes ago, Tony Brooks said:

 

As long as the tap is more or less at the top of the skin tank level AND the hose/pipe between it and the tank slopes upwards to the tap, then the tap should bleed the tank sufficiently. If there is a gap between the top of the skin tank and inlet pipe or the pipe/hose sloped down to the tap, air is likely to be trapped in the tank. Probably not enough to cause your problems, but air expands more than water as it's heated, so the more air that is trapped in the system, the more coolant that gets expelled as the system heats up. Without seeing the setup, I can't say more.

It does slope up to the engine and is pretty much as high as you could go on the side of the skin tank. 
so air should traverse back to the engine block

[Tony Brooks]

Just now, AlanJ said:

It does slope up to the engine and is pretty much as high as you could go on the side of the skin tank. 
so air should traverse back to the engine block

 

Yes, but I would not bleed there with the engine running because the coolant flow will be from the engine into the tank and this might prevent the air moving backwards along the pipe. I would bleed before starting then stop (say) 5 minutes later and try another bleed and so on. When all the top hose andt op of the tank is hot I would stop and bleed again in case the greater flow with the thermostat open has shifted some trapped air.

[Martin Nicholas]

Might not be quite your size by the sound of it; but these can be handy on top of a skin tank:

1/2'' BSP Automatic Brass Bottle Air Release Vent Valve for Heater Radiator DN15.

 

Proof read by a human.

 

[AlanJ]

Interesting idea. Never though of these in this context. Have similar on a couple of radiators at home that catch the air in the system. 
Given the size of the cap on my skin tank, I don’t know if they will do one that is big enough but makes you think of alternative solutions. 

[ditchcrawler]

1 hour ago, Martin Nicholas said:

Might not be quite your size by the sound of it; but these can be handy on top of a skin tank:

1/2'' BSP Automatic Brass Bottle Air Release Vent Valve for Heater Radiator DN15.

 

Proof read by a human.

 

I have seen them go pop and a nice little fountain is the result

[Ex Brummie]

22 hours ago, Martin Nicholas said:

Might not be quite your size by the sound of it; but these can be handy on top of a skin tank:

1/2'' BSP Automatic Brass Bottle Air Release Vent Valve for Heater Radiator DN15.

 

Proof read by a human.

 

Please do not use one of these. On a central heating circuit they are always under pressure, this will not be the case on your cooling and you could introduce air and compound your problem.

[Tony Brooks]

If my boat had needed  skin tank vent I would be looking for the required fittings to fit a radiator manual bleed screw. I have never known one to seize up, unlike steel plugs in steel tanks.

 

If anyone wonders why my boat did not need one, the answer is simple. It was build by a hire fleet to minimise potential problems, so it had a proper marine engine and the header tank was directly above and fed into the top of the skin tank by a short length of 2" hose.  It ran unpressurised and any air simply vented out of the tank.

[Tracy D'arth]

On 02/08/2021 at 09:04, AlanJ said:

 

 

When the buzzer when, the pipes to the calorifier and skin tanks were relatively cold (could easily be held)
On restarting the engine and when the buzzer did not sound, these pipes quickly got too hot to hold. 

 

It is an air lock.  Check that the pipe/s from the thermostat rise in a direction so that they self bleed any air out.

 

There is another possibility that I have experienced.   If the volume of water in the system is large, when it heats from being topped up there will be some expelled via the pressure cap. If then next time it is fired up from cold, there is insufficient coolant to fill the exhaust manifold, circulation  through the top hose and thermostat ceases, the manifold gets hot very quickly and flashes the water remaining in it into steam which causes more water to be lost. Stopping the engine and putting in a small quantity of water immediately restores circulation through the thermostat and the engine cools properly.

So really that is a self induced air lock.

[Iain_S]

Our last "overheating" problem proved to be the wire from the temperature sender having abraded insulation, after vibrating against the engine causing an intermittent low resistance path to ground. Slight giveaway was the temperature reading apparently moving rapidly up and down by 10 degrees or so

[Tony Brooks]

4 minutes ago, Iain_S said:

Our last "overheating" problem proved to be the wire from the temperature sender having abraded insulation, after vibrating against the engine causing an intermittent low resistance path to ground. Slight giveaway was the temperature reading apparently moving rapidly up and down by 10 degrees or so

 

and that is why I have been advising that the overheat most be tested to see if it's a true overheat or a lamp/buzzer circuit fault.

[AlanJ]

26 minutes ago, Tony Brooks said:

 

and that is why I have been advising that the overheat most be tested to see if it's a true overheat or a lamp/buzzer circuit fault.

I am confident it is an overheat but the comment from Tracey rings true also. 
when I changed the thermostat, taking the housing off, there was no coolant around the stat at that point. I changed the stat and didn’t think too much about it at the time. 
as it overheated again, I then flushed the system and re-ran the engine having filled the header tank. 
I wonder if there is a small leak that is causing the level to drop slowly (we ran for about 45 hours before it started playing up again) 

from memory, the coolant level is about an inch or so  below the top of the header. 

[Tony Brooks]

22 minutes ago, AlanJ said:

I am confident it is an overheat but the comment from Tracey rings true also. 
when I changed the thermostat, taking the housing off, there was no coolant around the stat at that point. I changed the stat and didn’t think too much about it at the time. 
as it overheated again, I then flushed the system and re-ran the engine having filled the header tank. 
I wonder if there is a small leak that is causing the level to drop slowly (we ran for about 45 hours before it started playing up again) 

from memory, the coolant level is about an inch or so  below the top of the header. 

 

That could well be true and finding it without a pressure tester can be a pain because once the coolant is up to pressure very minor leaks tend to evaporate rather than pool and drip. All you can do is look for rusty/antifreeze coloured stains while getting up close and personal with a running engine.

 

When you say "header tank" are you talking about a remote one or the one that s part f the exhaust manifold with the radiator cap on it? If it's the latter, note what I and Tracy said about engines venting so much water they air lock themselves when cold, but I have no idea why it should be OK for years and the sudden start doing it.