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Hi guys,

This is my Thornycroft Engine - it's just had the head skimmed and refurbished, water pump cleaned out, new headgasket, new thermostat, new belt. But it's overheating.

It gradually reaches about 80c over five minutes, then continues to climb. The thermostat housing (bottom right) gets hot, but the pipe you see leading to the manifold tank remains cold, and the manifold tank itsself only slightly warms. Any suggestions on how to proceed? I'm wondering if it's a duff thermostat but I'm reluctant to get it out as it's all nicely sealed.

 

Any help much appreciated.

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I have no knowledge of that specific engine, but problems like this immediately following major maintenance are often down to an airlock in the cooling system. Does it have a skin tank, raw water cooling or what? Looks a bit like a wet exhaust /raw water system but it's always best to ask since I don't have any experience of wet exhaust systems.

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Not the same engine, but i once read that removing the filler cap and running unpressurized for a while can help remove air locks. I usually do this after changing the coolant.

also are there any bleed points on the skin tank, thermostat housing etc?

Edited by Guest
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As above but it really does sound like an air lock. As per Catweasel advise, let the engine cool, take off the cap and run the engine. It would be best if the tank has not been overfilled and is about 2 inches from the rim where the cap fits. Watch the gauge for over heating and see if any bubbles are apparent in the header tank.

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Before the work the head gasket had failed and it was overheating, but seems to be worse now. I had a professional mechanic helping with the rebuild so I doubt the thermostat is upside down...

Ok, if your sure of that, because the symptom is exactly that of a thermostat upside down. Then try as catweasel said. Remove filler cap, top up with coolant, start engine, keep blipping the throttle up and down, from high revs to idle whilst watching the coolant level in the exchanger. If there's air trapped somewhere the level will rise and fall by a large amount, 'bouncing on the air' which should eventually be expelled gradually in small bubbles or in big burst of bubbles at the filler. Continue blipping the throttle whist topping up and watching the temperature gauge. When all the air is expelled and no more air bubbles the coolant level should moreorless stabilize, the pipes get hot going out to the skin tank and cooler on the return pipes.

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First thing I would check is the thermostat, dip it in boiling water and see if it works.

I fitted a new one to my engine and it was faulty, also check that the correct thermostat has been used.

If OK then check the water level in the skin tank and top up with coolant.The skin tank should be higher than the engine.

Could be an airlock as suggested.

 

(This is why I never completed the 2013 BCN Challenge)

Edited by Laurie.Booth
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The skin tank should be higher than the engine.

 

 

I can't quite work that out, as the top of my engine is about at water level, and the pipework falls from the header tank (outlet on the underside) and then runs horizontally to the top of the skin tank. The return line is more or less horizontal as well.

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I can't quite work that out, as the top of my engine is about at water level, and the pipework falls from the header tank (outlet on the underside) and then runs horizontally to the top of the skin tank. The return line is more or less horizontal as well.

 

Neither can I. It matters not a jot where the skin tank is relative to the engine as long as air can vent from it and the pipes and the the water pump can circulate the coolant.

 

Now if LB had said the HEADER tank I would agree.

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Heh, flipped the thermostat over and now it's holding temp just above 80c, probably slightly over because the cap is still off so the system isn't pressurised.

 

In my mechanic's defense, he's in his mid 70's and probably isn't as sharp as he once was (he eagerly volunteered his services free of charge because he hates retirement)...

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Heh, flipped the thermostat over and now it's holding temp just above 80c, probably slightly over because the cap is still off so the system isn't pressurised.

 

In my mechanic's defense, he's in his mid 70's and probably isn't as sharp as he once was (he eagerly volunteered his services free of charge because he hates retirement)...

That's good.

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Heh, flipped the thermostat over and now it's holding temp just above 80c, probably slightly over because the cap is still off so the system isn't pressurised.

 

In my mechanic's defense, he's in his mid 70's and probably isn't as sharp as he once was (he eagerly volunteered his services free of charge because he hates retirement)...

Glad it has been solved, so it was the thermostat in the end.

:)

 

Neither can I. It matters not a jot where the skin tank is relative to the engine as long as air can vent from it and the pipes and the the water pump can circulate the coolant.

 

Now if LB had said the HEADER tank I would agree.

Sorry you are quite right.

:)

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