Volvo Penta D2-75 mystery coolant leak

[Downeaster]

Losing maybe a shot glass of coolant per 4 hours of run time. I can see drips and splatters under the turbo and on the saildrive. I've been trying to track this down for months now. Today I found a possible clue.

The charge air cooler (after cooler) has a drain hole at the bottom (see picture below) that is supposed to drip out water condensate from hot air flowing over the exchanger element. It vents a good stream of air as it should, and probably some condensate as designed. But it is appears to also be spitting (sometimes, and only a tiny bit) yellow/green coolant so maybe this is where I'm losing coolant?

BUT! IF (??) I understand correctly the air cooler uses SEAWATER not coolant in its exchanger. So I'm a bit baffled... I know the air cooler can, normally, burp some oil from the turbo. And the splatter seems maybe a little oily. But it's definitely coolant colored.

Anyone have a suggestion or insight on what is going on? Thank you!!!

[DougR]

Given the location of the coolant drops, you might check around the turbo mounting adapter. The turbo is connected to the exhaust manifold/heat exchanger casting with an adapter housing, and the adapter housing contains coolant. The coolant gets into the adapter thru a passage in the manifold gasket, and exits the adapter via a nipple and hose and travels to the oil cooler.

If coolant is leaking from the gasket or the hose and nipple, it can get spread around by the aftercooler bleed air and become difficult to find.

Of course, if the head gasket is leaking at the back of the head, it can also end up in the same general area......

[Downeaster]

Thank you, DougR. I’m pretty sure it isn’t the adapter housing or hose.

A head gasket leak would be internal, correct? Wouldn’t there, in addition need to also be a leak inside the charge air cooler for the coolant to get into the air flow? Not seeing how coolant would get from head gasket to the internal air side of the charge air cooler?

It is significant, I think, that the coolant drips ar not very or at all diluted. This perhaps means it isn’t an exchanger pin hole or gasket as then it would be very diluted with sea water?

[DougR]

A coolant leak from the head gasket wouldn’t necessarily be internal...it could leak directly to the exterior of the engine and run down to the area of the aftercooler. Also, another potential source I didn’t mention earlier could be the freeze plug on the rear of the cylinder head. This would also leak undiluted coolant which would drip or run down in the vicinity of the aftercooler.

I don’t see any possibility of coolant being in the aftercooler. The aftercooler is sea water cooled, and there is no coolant anywhere near the air flow stream feeding the aftercooler.

[Downeaster]

Originally Posted by DougR

I don’t see any possibility of coolant being in the aftercooler. The aftercooler is sea water cooled, and there is no coolant anywhere near the air flow stream feeding the aftercooler.

Agree - and thank you for confirming my thinking there. Really helpful DougR - because now I can start following the other threads - process of elimination