First off: 1990 240DL 119,000

The other day I was on a 200 mile trip and after about an hour or so the engine temp guage moved up to about an eigth of an inch below the red line. I turned on the heater full blast and eventually the needle went down to about the middle again. It seemed to happan again when I was going around sixty and then accelerated to about eighty. Again, I turned on the heater to draw heat from the engine. The needle moved to the middle again and stayed there. I would say on the whole three hour trip this happaned about three or four times. I tried to determine what was causing the needle to shoot up - I thought it was when I was accelerating suddenly, but it happaned once when I decelerated quickly at a toll booth. The needle never got into the red zone - but it got up there - pretty close. What could be causing this? Bad water pump? Bad thermostat? I flushed and filled the radiator around 5,000 miles ago, I just changed the oil before the trip. I think it could be a failing water pump. Thanks for your help.

I had a similar problem a few months ago. The temp would be ok on my 40klm drive back from work. But about half way I had to drive a steep section of the highway and the needle nudged the red zone. Engine off for 20 minutes and the rest of the trip was ok cause it was flat and I was getting air thru the radiator.On the weekend I checked out the thermostat(I'd replaced it 18 months earlier) and one of the support arms for the pin spring thing had snapped.

I will replace the thermostat and water meter tomorrow and let you know what I find.
Marc

JWalker is right. When we hear any water temperature guage-related problems, the board is an immediate suspect. Does pounding on the dash cause the needle to move?

Also, try shining a light through your radiator from the inside out. I have a long-haired cat living in my garage that sheds it's own body weight in hair every week. I have to pull out the radiator and vacuum and hose the cat hair out of my radiator and condenser fins every few years. Bugs can also plug up radiators.

Check the thermostat and water pump first.

If not, then it could be the temp. compensation board in the temp. gauge. This is a very common problem, especially in the 1990 models. If it starts acting very erratically, going up and then not working at all it more than likely is the t.c. board. My 1990 has had that problem for awhile, I need to take it out and fix it before the hot weather arrives. Check the archives for repair details...

This is a long shot, but take a look at your temp. sensor and make sure it is working too.

Good luck,

Jim 90 244DL 213K

Try a new thermostat first, cheap and easy and the most likely. You do not mention coolant level, are you losing any? Belts tight?

Water pumps fail with the typical symptom of leakage out the shaft seal but they do not stop pumping.
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David Hunter

Thanks, no I am not losing any fluid at all. The belts are nice, as I just replaced the alternator.