Coolant loss into oil and no external leak! Help

[Mass]

I’m working on a lbz CCLB with almost 300K
It has coolant loss with no external leak there is coolant in the oil when I go to drain it, the coolant pressure is getting into motor.
I cleaned the oil and took the truck for a drive and there was no white smoke out of exhaust and glow plugs are not rusty (the truck was sitting for a year) and look normal, so I don’t think it’s a blown head.
How else can coolant get into oil?? But no oil in coolant??
What other diagnostics steps to take?
Thank you !

 

[shakenfake]

Oil cooler

 

[Mass]

Oil cooler

I thought that but Wouldn’t there be oil in the coolant? Oil pressure is higher then coolant pressure
Thanks for your reply

 

[Mass]

Oil cooler

thoughts on maybe the water pump?

 

[TheBac]

x2 -- probably the oil cooler. These engines are 20+ years old now.
My experience, water pump usually doesnt leak inward, just coolant thru weephole.

Be safe over there.

 

[DAVe3283]

If the oil cooler is leaking, I would expect to see mixing both directions. When the engine is running, oil pressure is 15-60 PSI and coolant is 15 PSI, so you would get oil in the coolant. But when the truck is shut off, oil goes to 0 PSI but coolant stays at 15 PSI for a while, and will put coolant in the oil.