I have a 1993 240 that is overheating and forcing coolant/steam out of the reservior container. This has happened twice. Both times when the car was idling.

In November of 2004 I flushed the coolant system and replaced the coolant with a 50/50 mix of new coolant and distilled water.

This issue just occured, last week.

I have replaced the thermostat, but believe that is not the problem because I checked it in hot water and it opened.

Another thing, the temperature gauge always showed the car at normal operating temperature. It never even moved away from the 1/2 mark.

Any ideas?

-AL

 

A few things come to mind. Loose/ slipping belt for the water pump, defective radiator fan, switch or relay and a defective reservoir cap for the easy stuff. Harder to deal with would be a loose water pump impellor and a clogged radiator.
The temp gauge has a compensation board installed on the dash cluster pc board. It was used after '85? to even out the normal temp range of lows and highs, and keep people from getting excited about a little too high or too low reading.It will not show an overheat condition until it gets extremely hot, and basically functions like an idiot light. IPD sells a kit to bypass the silliness.

 

I agree check the belts,water pump,Radiator, and Fan.

 

After reading the replies, and further investigation, I will replace the overflow container cap and see what happens. The 240 uses a pressurized cooling system, and it is possible that the cap which is supposed to blow at a certain PSI has failed and blows earlier. I feel this may be the case because the engine temp gauge indicated that the engine was at normal operating temperature, and a clogged radiator, broken thermostat, loose/slipping water pump belt, or defective radiator fan would have raised the engine temp before blowing out reservoir cap. I will post an updated and let you know if this solves the problem.

 

Since my last posting I have replaced the overflow container cap and have not had a reoccurance of coolant/steam being forced out of the reservior container.

Root cause: broken radiator overflow container cap