I believe that Mach 4 did a thorough investigation on the oil cooler thermostat for his OM617 engine, might want to find that thread and read up.

Basically the choices are to re-engineer and find some other way to control oil flow via the cooler, or live with it.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC