Hello, I just bought a 1989 190E 2.6 and it didn't come w/ the owner's manual. I want to do an oil change but i don't know how much to put in or what grade to use.

I also have a problem w/ the engine temp. Whenever i'm in traffic my temp gauge slowly rises and then when I get at a constant speed, it goes down. The highest it's gone is like 110C and I don't know if it could have gone higher because I reached my destination and quickly shut the car off (kind of freaked out). On the highway it always stays at a cool 80C. What's going on??

Your engine takes 6 quarts of oil. But put in five first to avoid an overfill and run the engine till hot and check the oil level, add more if needed.

As for your cooling problem, it could be many things:

Low coolant level due to a slow leak.
Weak coolant, improper coolant, improper mix.
Faulty/failed fan clutch or aux fan.
Blocked radiator.
Air in the system.
Faulty water pump.

Sometimes a new expansion tank cap fixes the problem. If you don’t know when it was last done have the cooling system pressure tested, flushed and refilled with proper MB coolant.