thorneycroft water loss

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owen

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. my thornecroft t90 has been losing some water.. the water in the heat exchanger has been dropping and needs topping up regularly. the engine works fine and there is no oil or emulsion in the water or the oil so i feel it is not the head gasket. the inlet and outlet hoses are tight and there are no leaks . the water pump likewise has no rust patches ar obvious leaking. i was wondering if it could be possible that the heat exchanger could be leaking fresh water into the sea water through the stack. is this likely? or is it more likely that if there was a leak then the seawater would leak into the fresh?? has anyone had a similar problem and has anyone investigated a bowman heat exchanger?
 
I take it you have checked the engine oil for emulsification which would indicate a duff head gasket. If that's eliminated, more likely fresh water to raw as the engine side is pressurised once operating temperature is reached. You might be able to test the stack by taking the ends off the heat exchanger (engine not running!) and seeing if water comes out when there is pressure in the fresh water side.
The easiest way to increase pressure would be to blank off the filler and pump air into the overflow pipe.
I have the older type Bowman manifold heat exchanger with alloy ends, not the rubber caps and managed to get a fabrication shop to weld up some of the alloy casing. The stack itself was ok.
A new exchanger will not be cheap but they are available through ASAP Supplies.
 
i top up the same engine 72hp thorny every time I check the water in the header tank, it usually takes just a little less that a cupfull to overflow. I believe that once the engine heats up the expanded water is blown out through the header tank cap. I hope this helps, if you are loosing more water than this then you may have a problem.
good luck Ian
 
On my old boat, my BMC 1.5 used to lose some water too.

It turned out to be a knackered water pump, despite no obvious signs of it leaking. New one fitted, and the problem was solved.

Also worth pulling your heat exhanger tubes out, and checking the seal against the rubber ends. And also, check all the core plugs for leakage.
 
if you have the heat exchanger with the rubber caps on each end, try taking them off,[both clips ] clean up the ends and refit. the water could be leaking past into the salt water system. I had the same problem it cured it.The heat exchanger normally works at about 1" below the bottom of the radatator cap. hope this helps.
 
thank you very much for all the replies. does the saltwater stack come easily out of the alloy exchanger?? i hope i dont need a new bowman as the price is £400+
 
The stack should come out fairly easily, but if theres a buildup of crud, you may need to gently persuade it out. A piece of wood and a small hammer should do the trick, and just tap it back and forth to loosen the crud, washing it out regulary until it pops out.

My old once was horrendously bunged up with rust pieces and other crud. Not a wonder it started overheating over about 3/4 throttle!
 
HWMBO, not Becky.

We have a T90 and last year, or the one before, we started loosing a lot of water. It turned out to be the water pump. (Fresh water circulating). There is a witness hole in the pump body through which it was gushing. Since the paint on the water pump did not match the rest of the engine we surmised that it had been replaced before at least once.

We got a replacement pump from ASAP, wery quickly and at a good price. Do be careful as there are two types of mounting. one has three bolts, and the other has four. You need to specify when ordering.

There is not much that the average yottie can do to repair the pump as the bits are pressed in. They do a part exchange IIRC.

All the best, Richard.
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