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Thornycroft 108 overheating


Mike.w

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Hi,

Can anyone help please.

I have a Thornycroft 108 in 27ft Seamaster. It's my first cruiser and my first Thornycroft.

A couple of weeks ago we broke down with the engine overheating  and leaking from the waterpump.

This I replaced along with the supporting hoses and I thought that was it.

Unfortunately not. We went out again yesterday, with a couple of other boats, only break down again, overheating again.

This time it's not the waterpump. A couple of the other boat owners had a look and one of them checked the filter (the one that filters the canal water) this was completely blocked.

That was cleared but the engine still overheated. We limped home stopping every ten minutes to cool down.

Today I have removed the impeller, but that looks ok and have removed and tested the thermostat which is ok.

Does anyone have any ideas?

The one clue I have been given is that there doesn't appear to be any water spitting from the back when travelling.

 

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Welcome to the forum.

Perhaps an airlock in the cooling system? Try refilling the system and starting the engine, with the header tank filler cap off, and see if water bubbles and moves around, and if the level drops. If so , top it up till it settles. Remember that à header tank should not be full when cold, to allow for expansion when the water is hot. Header tanks are also called expansion tanks.

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Sounds like you have indrect cooling. There are two cooling water circuits and two water pumps. One circuit runs though the engine block to a heat exchanger, which transfers the heat to the second circulation. This takes canal/river water in, through some sort of filter, through the pump then to the heat exchanger (which may be built into a water cooled exhaust manifold) and is then injected into the exhaust pipe.

If you normally have water in the exhaust, but now there is none, then the second circulation is not working. Check for blocked filter, failed pump impeller, failed pump drive belt or blocked hoses. If those are all OK you may need to take the end caps off the heat exchanger and check the tubes are unblocked.

You should have a header tank for the engine circulation. It may well be combined with the heat exchanger/exhaust manifold, with a car radiator type cap on it. Remove the cap (when the engine is cold) and check the coolant is full. If you have had a leaking water pump it could well need topping up.

 

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  • 2 weeks later...

Thanks for the help, problem solved.

The impeller wasn't spinning! due to a jubilee clip not being tight enough so when the impeller tried pulling water, all it did was suck air.

Took ages to find this, I had the impeller off 3 times!

But now all good, thank you for the advice.

  • Greenie 2
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