[Thejarhead]

Did you torque the head gasket correctly? I know it’s a multi step process.

I believe it’s 30flbs then 44flbs then 90 degrees then 90 degrees again. Starting in the center and alternately working toward the ends. Someone correct me if I’m wrong. Did you forget the second 90 degree turn? The oem head bolts are single use TTY unless you used APR aftermarket bolts. Did you use new bolts?

Did you use an oem thermostat, aftermarket tends to be junk.

 

[Thejarhead]

It might be worth pulling the thermostat and dropping it in some hot boiling water just to verify that it does open.

Oil coolers do fail. Usually they just leak externally but sometimes that leak is internal.

 

[Thejarhead]

Glad it was relatively simple and you seem to have solved the problem. Good job.