Volvo Penta Coolant Leak Help

[kyle23462]

Ran the boat for about 20 min today and noticed a coolant leak. Found coolant leaking down onto catch pads under engine. A little background and info before we start.

Engine is a 95 Volvo Penta 7.4GL, complete rebuild in 2010, approx 250 hrs since rebuild. This is a fresh water cooled block with raw water cooling for exhaust, basically a half system.

Noticed the coolant leak more in port side but there is a little on the stbd side as well.

It almost looks like it is coming from the oil cooler area in the port and freeze plug side on the stbd.

The kicker with this is everything is dry, hoses, freeze plugs, heads, you name it and it is bone dry. Tried looking for leaks in the slip, boat in neutral up to 3k rpm and nothing. Pulled the boat out, on the trailer with fresh water hooked up, up to 3k rpm and no leaks.

Changed pads out, back in the water for another run. Up to 3k rpm under load for about 10 min and back to the slip and there was coolant on both pads?

It almost seems it leaks under load but otherwise it doesnt. Temps ran the same as always, 170 at idle and 180ish under load. Damn if I am not stumped on this one. We have checked the oil and no water is present.

Had a mechanic buddy help me during this whole process and he is stumped too. Anyone ever had an instance like this? Any help would be greatly appreciated.

 

[jerryjerry05]

Anti freeze shouldn't be that hard to trace???
Sometimes a black light will show where the leak is?
Does the reservoir have an overflow tank?
Pics.

 

[kyle23462]

Anti freeze shouldn't be that hard to trace???
Sometimes a black light will show where the leak is?
Does the reservoir have an overflow tank?Pics.

I agree it shouldnt be hard to trace. After all the troubleshooting everything is dry. Thats the part that has both of us stumped. I do have an overflow tank on the stbd bulkhead forward of the engine, no leaks out of there. Is there a way to pressure test the coolant system without running the engine?

 

[Bondo]

I agree it shouldnt be hard to trace. After all the troubleshooting everything is dry. Thats the part that has both of us stumped. I do have an overflow tank on the stbd bulkhead forward of the engine, no leaks out of there. Is there a way to pressure test the coolant system without running the engine?

Ayuh,.... Just like a car, use an automotive coolin' system pump to pressurize it,....

 

[Scott Danforth]

add tracer dye to the coolant and use a black light. dont get it on your clothes, you will never get the tracer dye out :facepalm:

 

[kyle23462]

Tried the pressure test as stated above, tested the system at ambient temp then again once the engine had ran and came up to temp. 170 degrees.

Pressurized to where the coolant overflow bottle was starting to vent, once the pressure dropped to where the cap wouldnt vent pressure stayed steady for hours.

Looked all around the motor and on the catch pads and no leaks anywhere once again.

This is only happened when the engine is under load, ie; props spinning. Any other ideas before I break down and take this thing to a Volvo mechanic

 

[jerryjerry05]

Maybe, just maybe??? The cap is the culprit?
What pressure is it?
The unit holds pressure? while it's being tested with the cap off.
The pressure tester should have a cap tester if it's a good one?
You testing with the antifreeze in or out?

 

[kyle23462]

I installed a gauge and hose off the overflow port on the container. Used a bicycle pump to pressurize through the line. I did try a different cap and the pressure relieved at the same spot on the gauge. When I started to pressurize the system the overflow container filled rather quickly, not sure if this should happen or not. I have ordered a combustion test kit for the coolant and it should be here later today. Going to try that to check for bad head gaskets/block. If that test comes back good, which I have a feeling it is going to we plan to mount a go pro in the area where the coolant is and go for a test run. Other than that I cannot think of any other way to check this. Thanks so far for all of the help