1987 300SDL OM603 NO OIL FLOW TO THE OIL COOLER!

[bentrod]

Hello, my 1987 300SDL has NO flow to the oil cooler!
I have 2 of these cars and my problem one has a cold oil cooler.
The lower pipe is hot a few inches from the oil filter housing but the top is hardly warm - probably from just its proximity to the engine.
And the oil cooler is just outside temp anywhere you feel it.
My other car you can easily feel the oil cooler is plenty warm and I know that one is working good.
I've driven the car 20 miles, some high throttle opening and up a few hills to ensure the engine is fully warmed up.
I removed the metal lines and it was easy - and messy - to blow air through the oil cooler.
I can't find any good info on a so called oil filter housing thermostat for the OM603 engine!
Can it be a oil thermostat and check valve issue!
Can I replace these parts inside the oil filter housing? ( removed from the engine )