Engine overheating

[Tracy D'arth]

57 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. 

Mystery slow water loss can often be the water pump leaking, hard to see, hard to be certain as it spins off and evaporates before it makes a puddle.

[AlanJ]

with regards the header tank - it is just the top of the engine with a radiator cap. Apologies if I am using incorrect terminology here - just let me know what I should be calling it.

[Tracy D'arth]

57 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. 

Mystery slow water loss can often be the water pump leaking, hard to see, hard to be certain as it spins off and evaporates before it makes a puddle.

1 minute ago, AlanJ said:

with regards the header tank - it is just the top of the engine with a radiator cap. Apologies if I am using incorrect terminology here - just let me know what I should be calling it.

It is likely that you are referring to the exhaust manifold and combined heat exchanger, usually with the front end connected to the thermostat housing hose and a radiator cap on top. It is a header tank and is designed to cope with the expansion of the coolant as it heats up so its not full to the top when cold.

[Tony Brooks]

35 minutes ago, Tracy D'arth said:

Mystery slow water loss can often be the water pump leaking, hard to see, hard to be certain as it spins off and evaporates before it makes a puddle.

It is likely that you are referring to the exhaust manifold and combined heat exchanger, usually with the front end connected to the thermostat housing hose and a radiator cap on top. It is a header tank and is designed to cope with the expansion of the coolant as it heats up so its not full to the top when cold.

 

Two points.

 

Leaking water pumps don't tend to be consistent, so they leak and stop leaking (in the early stages) when they think they will, so that tends to go with your symptoms.

 

The header tank in the manifold is basically designed to cope with the expansion of the coolant in heat exchanger engines (indirect raw water) and not skin tank boats because the ski tanks can hold  a lot more water so expand more when heated. Hence, the can bow a lot of water out, so they airlock when cold.

[MtB]

14 hours ago, Ex Brummie said:

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.

 

I have one on my skin tank and it works very well.

[AlanJ]

Thank you for all the advice so far.
So I was back at the boat today, this is what I found.
First check I made was the water level relative to the thermostat. Removing the stat, the water was about about 2 inches below the bottom of the stat. This was lower than it had been.

So, replaced the stat and housing and topped up the water level to about 1cm below the top of the header tank on the exhaust manifold (and above the level of the stat).

Also checked the venting from the top of the skin tank, that was clear of air.

 

Ran the engine for 30 mins taking regular temperatures with an infrared thermometer.

I left the radiator cap off to allow for any "burps" to be seen/released - none were witnessed.

 

Temperature got up to 50 degrees on the surface of the thermostat housing (engine was just idling) 
Pipes to the calorifier and skin tank both got quite warm (about 35 degrees surface temp). The return from the calorifier slowly moving up from the 18 degrees ambient temperature to about 25 degrees; the skin tank return pipe didn't budge from 18 degrees. The top surface of the skin tank got to the same temp as the feed from the engine with decreasing temp as  I worked down the side of the tank.

The water in the calorifier did start to warm up as well.

 

I did notice the calorifier is above the engine block uphill slopes on both sides 

 

So, I'm confident that it isn't an air lock in the system

I am confident that when it does overheat, it truly is overheating (the buzzer didn't go off today when testing but this was after adding coolant to the system)

I do think there is a slight leak somewhere in the system - this is going to be the fun bit to find. I have a suspicion about the calorifier as there is residue where this lives. (it is in the engine bay on the Uxter plate?). I have tightened the jubilee clips on these pipes.

Given everything is in the engine bay, hopefully it shouldn't be too hard to find. 

I am concerned that the calorifier could hold an air lock in the circuit but the temperature readings did not suggest this was the case. I think I will look at adding a vent tap to the top feed pipe.
 

So, I think short term it is just a case of keeping topping up the header tank to make sure we don't get so low on coolant again. Obviously, too low is not as low as I thought/expected.

Next is to locate the slight leak and remedy.

Given my suspicion on the calorifier and it being above the engine, adding a vent here will result in connections being taken off/redone and may well fix the problem

 

[Tracy D'arth]

I would doubt that the calorifier will cause an air lock in the top of the engine, most are higher than the heat exchanger.

 

If there was no water in the thermostat housing, it is seriously short. Any water remaining in the bottom of the exhaust manifold/heat exchanger will then flash to steam very quickly which will cause an instant loss of any circulation in the engine causing overheating as you have experienced.

 

Find the leak.  Water pump, pipes, calorifier, even the skin tank corroded through to outside?