[Lawrence Coppari]

Are your fans coming on when the temperature rises?

Car should have the thermostat installed. I don't know about this car, but a Mercedes will not cool properly without one (no kidding!).

A number of years ago I was having a problem with my car wanting to overheat when going up hills at low rpm. Car would cool properly at higher rpm like on the track. I replaced the water pump and the problem went away. Evidently, the impeller had developed too much clearance between it and the pump body. This was due to corrosion increasing clearance between impeller and housing. Car has not had a cooling problem since.

Do you have a proper mix of antifreeze and water?

Do you have a collapsed coolant hose?