1992 300E High Engine Temp, Good Coolant Level
 

I have a 1992 300e with 116k miles. This morning I fired the car up and the coolant light was on. Checked the coolant level and it was good. The light when off in less than 30 seconds. Then, I drove to work and was sitting in a drive thru and the engine temperature skyrocketed upward (it was 81 degrees outside). I turned on my heat and the engine temp fell pretty quickly.

If my coolant level is good, what other checks can I do to try and find out why my engine temperature is going up like that?

It sounds like your coolant level is low. How did you check? It's a bit tricky to check because the coolant is clear ish.

Top it off when it cools down, and start checking for leaks.

Either the temp sensor is faulty or you have a head gasket issue. Do you have an infrared tempature gauge?

Check out this 'list' on my page . . . here.

Make sure that the coolant/water ratio is no more than 50/50%

If the radiator is original it's probably toast!

Thanks for the replies so far. I do have an infrared thermometer. I added a little more 50/50 coolant in there today. By the time I got home the temperature was still up to about 110 degrees celcius but would not go any higher. I parked, turned off the engine and opened the hood and saw that the coolant was BOILING in the reservoir. I'm letting everything cool down, and I will see if the auxiliary fan is running.

Should I use the IT to measure the coolant temp?

Yes, it's #1 in the table. . . replace your rad cap!

possible air pocket?? also try draining coolant out and then refilling according to mb procedure

Does the temp drop with a little speed, which creates airflow? if so, suspect the fan clutch.

I just got to work this morning with no abnormal engine temp spikes and no boiling coolant. Both of the fans are working too. I am going to start with the radiator cap and see if that fixes it. If not, I will be back. Thanks for all of your input guys!

If you can see or feel coolant boiling in the tank - your radiator cap is either a wrong type or bad.

If you are sure its good - and you see that your engine fan is not roaring when the engine accelerates at such hot engine temperature - your cooling fan clutch is shot.

Your auxiliary fans should never come on in ordinary circumstances - only in very hot weather and in extreme stop start traffic or started up by the AC switch.. The viscous fan should do most of the cooling in normal operation in stop start traffic.
The viscous fan becomes moot over 25 mile per hour - airflow through the radiator should do all the cooling.
If you are driving fast and the engine temperature is high this indicates a poor water circulation or lack of pressure in the system. Either your thermostat is not working properly, there is a leak in the system somewhere, your water pump is failing and not circulating the coolant fast enough or you have a blockage in the radiator or the cooling passages.
Of course you could have a failing head gasket that is causing heat to get into the cooling system.
You should take your car to a Mercedes independent service agent and get your coolant system pressure tested.