gentlemen: I have a customer with a 96 3500, with low miles(under 100k). I noticed a small amount of coolant contamination in the crankcase (observed coming from the breather tube). I ruled out the oil cooler as I have seen a few fail and they always put engine oil in the cooling system. This truck has no evidence of that. I finally removed the head to explore. I saw no obvious failure of the gasket, and no visible cracks in the head casting, cyl. walls, etc. No warpage or pitting. The new Cummins gasket had been updated for sealing in this area, with more rubber bead in areas between oil and coolant passages. I hoped for the best and reassembled it, but it has not cured the problem. I know there are frost plugs behind the side cover on the block, which could theoretically leak and cause this problem. Is there anything else anybody has seen? Thoughts? Opinions? Thank you.

Dave

 

Something I have seen in gassers is a cracked block.

 

You should first verify it is indeed coolant with an oil analysis.
Pure water in diesel engine oil often takes on an antifreeze green color. In the blowby it can come from engine condensation burning off or engine washing.
Condensation is most often a problem with vehicles that are subjected to short trips.

 

It is definitely coolant. Condensation was my first thought, as it showed up as a light tan scum that looks like pus. A quick taste confirmed that it was antifreeze.
(Yuck I know. But it works)

 

Depending on the customer, what I have done to help locate leaks like that was to pull the pan and pressurize the cooling system. Hopefully you can see the area(s) where it is coming from. Try putting a cooling system pressure tester on the rad and start the truck. If the pressure rises, it is a compression leak. It might take a while to build pressure though. You may also put the truck out in the parking lot and put a stick on the throttle to hold the rpms up to about 1200 too.
Tom

 

Pressurize the coolant system and see if it holds pressure. If it is loosing pressure quickly look for coolant leaking out on the floor. It may not be a completely "internal" leak. Im thinking you had a crack or two in your head. probably not visable but have it magnafluxed and see what happens. I really hope it isnt the head, they cost every bit of a thousand dollat bill.
Good luck
Scott

 

Did you machine the cylinder head head gasket surface before you put the head back on?

 

I went over the gasket surface closely with a straightedge and it was well within Cummins specs, so I decided against planing it.
I left the pressure tester on it for quite a while and it did not drop. It seems to be a very small leak.
I agree the possibility of a small hidden crack in the head may be likely. Magnafluxing would be the answer.
Thanks to all for the replies.

Dave