Gray green substance under oil cap - Cummins ISX15

[Rawze]

Looks like coolant in oil. Even if you have red coolant, it usually makes for green-ish tinted slime.

Any coolant seeping into the oil system will eat the engine up alive real fast. - Pull the oil pan off it, pressurize the coolant system to 20-PSI and let it sit over night. Take no chances with it...

(04-06-2018 )Rawze Wrote:  ...
- We let it sit over night with 22-PSI pressure on it until next morning. Low and behold, we searched and searched and there was zero signs of coolant getting into the oil at first. Sometimes it is obvious, but sometimes it is hard to find. We wiped everything down and spun the engine a few times over by hand and could not immediately find any kind of coolant intrusion problem even though it is clear that there is a problem with the head, a gasket, liner... something. After looking and wiping things down under the engine, we decided turned it by hand some more ... slowly to see if we could get a better view at each cylinder. While turning the engine over by hand very slowly, when piston number 5 came up on a compression stroke, it started to gurgle and tiny droplets of water/coolant started to pour down the inside of the liner wall. Number 5 piston was leaking coolant out of the bottom of the piston. So far this tells us that there is a problem in the head or the head gasket.
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ref: http://rawze.com/forums/showthread.php?t...6#pid25356