1989 300 E Overheating Problem
 

I have a 1989 300 E and when I am driving the temperature stays at 80 degrees celcius, but when I come to a stop it climbs to almost 120 degrees. When I start to go again, it drops back down to 80 degrees.

Before this problem, the temperature of the car is always at 80 degrees and never moves.

Please help.

Check to see that all the fans are on full blast when the temp is near 120. If they are then get your thermostat changed first, its probably the cause, then proceed from there.

Check the auxiliary fans. They can run at two speeds: the lower speed is activated by the high side pressure of the AC, while the second level is activated by a coolant temperature above 105C.
It looks like the fans do not operate at all. You could check fuses and relays (in the relay compartment nest to the fuse box. I think the fans themselves tend to seize as well with age. Then there is a resistor or connected electrical wires that may burn.
Good luck, Bruno

I think your fan clutch is going bad. If not, I second the aux fans idea.

With engine running, ask someone to turn it off while you look at the main radiator fan. It must stop almost inmediately after turning the engine off. If it keeps spinning, fan clutch is dead.

Looks like the aux fan/fans is not operating as it should. If the fan itself is working by applying 12V to it, then the problem is either the temperature sensor switch or the fan relay. On my 87, 260E, this is the third sensor (has 3 pins, 2 for fan and one for Klima relay) on the engine from the windshield side. Pull the cable/connector off that sensor, and short the terminals of the connector when the car is hot (>105 degC), if the fans come on after shorting and dont come on before shorting then the temp sensor is bad.

Make sure the radiator and cooling system is full and has no air bubbles.
It sounds like you are low on coolant. When you stop, the water pump cannot maintain flow.

Try this at a light, rev the motor (in neutral) if the temp goes down, then it could be the coolant level.

I would also make sure there is no debris on the front or back side of the a/c condensor and front side of radiator.

The best way to clean this area is to pull the radiator so you can clean the front and back of condensor.

While the radiators out, you might want to have a shop look it over. It could be plugged up.

If you're cool at highway spped and hot at idle or driving slower, you may simply have an have an air flow issue.

Another possibility might be your water pump.

Quite frankly, there's a long list of things that can cause this and some have already been mentioned above. Put together a check list from the replies you receive here and go thru it.