Fresh water overheat

[John G]

Bavaria 30 Volvo  D 1-20. Engine running fine for 2 hours then overheat alarm. Coolant forcing its way out of expansion tank. Clearing very hot. Raw water circuit working normally with water exiting the exhaust and exhaust temperature sensor (i fitted) normal. Any help gratefully received

[SYJetzt]

Maybe one or more of the following issues:
Not enough raw water flow, raw water circuit partially blocked,
impeller ripped,
filter clogged .
Thermostat not working.
Head gasket blown.

[Diverphil1]

as sy posted but add to check exhaust elbow, a pinhole in the raw water to exhaust manifold would let exh pressure into the system. before it gets bad enough for your coolant to escape.

[sunshine]

I think some people have reported an air lock in the coolant side, leading to overheating. Cure was to make up a little bracket to raise the expansion tank to make sure its the highest point in the system.  I've never had this problem, so cant comment on how real a problem this is, or how effective a solution.

[John G]

I have taken the front and back covers off the heat exchanger and cleaned it all up. The problem i have now is refitting the little rubber elbow tube on the back off the exchanger to the exhaust elbow. It seems impossible to fit. I'm just wondering if i need to unbolt the exhaust elbow to manage it ?  VOLVO PENTA D 1-20

[sunshine]

Yes, that's the only way I could get it back on.  Back off the elbow, refit the tube to the elbow end first and as you tighten the elbow it will draw tube back onto the heat exchanger.  You might need to remove the air filter first, I cant remember.  There's a 8mm bolt accessed from under the bulkhead.

In theory you should use a new exhaust gasket.  You might as well take the elbow right off and give it a good inspection including the water injector while you are at it, checking for corrosion and excessive soot buildup.