Thirsty engine - BMC Diesel

[SimonA]

My BMC 1.5 diesel seems rather thirsty. I fill the header tank (bowman) to about 3/4 full (so about an inch or two from the top), run the engine for an hour or so and then find it takes about 1.5 to 2 litres of coolant to top back up to the same position. The engine does not overheat.

My first thought was maybe the head gasket, but I have no white smoke, no mayo under the oil cap, no sign of oil in the coolant or coolant in the oil, the engine starts first time and does not overheat. However if I start the engine without the filler cap on the Bowman heat exchanger tank I get a whiff of smoke and then the water starts to overflow, it doesn't seem to have any bubbles in it.

Today I took the thermostat off and found it covered in Jelly, I think this is a sign of the wrong coolant being mixed together? There was coolant under the thermostat, but none the heat exchanger side of the thermostat (took the pipes off an no coolant run out).

What's the forums opinion on this? Does it sound like a blown head gasket or an airlock in the system somewhere (wouldn't explain why I lose coolant). I can't see any signs of external leaks unless the leak was in side the clarifier.

Which way does the coolant circulate in a BMC? Does it come out the heat exchanger and into the thermostat or the other way?

 

[aquapower]

My BMC 1.5 diesel seems rather thirsty. I fill the header tank (bowman) to about 3/4 full (so about an inch or two from the top), run the engine for an hour or so and then find it takes about 1.5 to 2 litres of coolant to top back up to the same position. The engine does not overheat.

My first thought was maybe the head gasket, but I have no white smoke, no mayo under the oil cap, no sign of oil in the coolant or coolant in the oil, the engine starts first time and does not overheat. However if I start the engine without the filler cap on the Bowman heat exchanger tank I get a whiff of smoke and then the water starts to overflow, it doesn't seem to have any bubbles in it.

Today I took the thermostat off and found it covered in Jelly, I think this is a sign of the wrong coolant being mixed together? There was coolant under the thermostat, but none the heat exchanger side of the thermostat (took the pipes off an no coolant run out).

What's the forums opinion on this? Does it sound like a blown head gasket or an airlock in the system somewhere (wouldn't explain why I lose coolant). I can't see any signs of external leaks unless the leak was in side the clarifier.

Which way does the coolant circulate in a BMC? Does it come out the heat exchanger and into the thermostat or the other way?

It comes out thermostat through heat exchanger and into circulating pump, the calorifier should come out of the head so it can still circulate with stat closed and into circulating pump, I would first carry out a pressure test to see if there's any leak and while the stat is out would fit a new one as they are only a couple of pounds and check the old one in hot water to see if its working.

 

[david_bagshaw]

I would bypass the calorifier to remove it from the equation, as the heat exchanging tube can leak, but equally it might leak the other way as well so first of all leave cap off heat exchanger and the fresh water system pressured up over night. if it overflows, there is the culprit.