How hot should the oil cooler feel?
 

My oil cooler feels cool to the touch after long drives. Should it?

Cool Cooler
 

According to MB service manual, it just says "warm to the touch". I forgot the thermostate rating, but it was hot enough that it would be noticably warm.

one end should be HOT after getting the car up to running temperature.
As in cannot hold with your bare hand for more than a few seconds!
I can't tell you right now which end (I just drove the W124 this afternoon) but I suggest that if its not getting HOT, the thermostat in the oil filter cannister might be stuck.

Oil thermostat should open around 110*c oil temp.

If it's cool to the touch all the time, I check it out asap. Oil gets very thin above 110*!

With the engine at 80*C, my oil cooler is warm to the touch but not hot at all at the top, but HOT at the bottom. I don't know if thats good or bad but its one more observation to add to this thread.

If I drive gently mine stays cool or warm, but if I drive at a quick pace or do a lot of high rev acceleration, it gets quite hot. I can always tell when it is in use because my oil bars fall to about 1.3 or so(at idle), when its closed it is just above 2 bar. I burned myself on my oil filter canister today while adjusting my Injection Pump damper pin, which was bolted all the way in, as tight as it would go, I have no idea who did that to it. I have it several turns out, and its a noticeable difference.