My 1987 245, 223K, overheats occasionally. The temp gauge needle will go past the midpoint almost to the red zone at which I turn on the heat and the needle drops. It happens either on the highway or going up a hill in town. AC is off since it doesn't work, which makes turning on the heater at 90 degree temps even more unbearable. The car received a new waterpump 2 years ago, new radiator last September, and a new thermostat 2 months ago because the engine was running too cold. Now, with the warmer weather, it seems to be running too hot. There are not leaks anywhere, and the coolant has been replaced 2 months ago. Engine itself has been steam cleaned a few months ago, so it has no crud on it. Any suggestions? It is due for its 3000 mile oil change.

My car was overheating for a while and I tried everything you did, but nothing worked. I think the only things it could be is the temp guage not working, or the fan clutch might not be working, or you have an internal leak. My car is at the shop today and it turns out i have the worst of the three. My head gasket was bad. I hope your car just has a simple problem not like mine:(

Charles 1985 245ti

My car was overheating for a while and I tried everything you did, but nothing worked. I think the only things it could be is the temp guage not working, or the fan clutch might not be working, or you have an internal leak. My car is at the shop today and it turns out i have the worst of the three. My head gasket was bad. I hope your car just has a simple problem not like mine:(

Charles 1985 245ti

My temperature would shoot up into the red at random. I would drive around in the summer with the heat on too. My problem was a wire to the temperature sending unit that had lost its insulation. It would ground sending the temp up. Replaced the harness and the sending unit and it is now fine.

Simon 80 245 285K

Are you certain that the car is truly overheating?

A faulty temperature compensation board will sometimes give a false high reading. It doesn't make sense that it would be overheating at highway speeds, unless the coolant isn't flowing.

Removing the temperature compensation board and hard-wiring around it is pretty straightfoward if you're comfortable with using a scredriver to remove the instrument cluster and using a soldering iron to run a wire between two pins. The board is prone to failure and is really unnecessary -- all it does it "smooth out" the temperature reading so it always stays at "normal" rather than fluctuate with the actual temp.

Before I replaced the TCB on my wagon, I thought it was overheating all the time.

I wish I could think of a simple way to determine whether your TCB is at fault or not, but I can't off the top of my head. I suspect that one could somehow measure the signal directly at the sensor, but I'm not sure if it puts out a voltage or a resistance or what normal values would be. Anyone?

1. Radiator checked for blockage and flow. It may be blocked and need to be rodded out or a new radiator. A good radiator shop can do this.
2. Viscous fan may not be working properly.
3. Fluid passages in engine may be partially blocked. (Do 1 & 2 first)
4. Water pump and/or thermostat. (I replaced the thermostat a couple of times because the new ones did not work)
5. Engine timing way off.
6. Air/fuel mixture way off.

Your radiator is probably partially blocked.

Take a good look before spending unnecessary money.

Lawren.

But the radiator is not even a year old, approx 8000 miles...I'll have someone check on the other stuff (yeah, those thermostats!). Thanks for input, all of you.

Just a suggestion, but my wife's 1990 240 was having the same problem and it turned out to be the Fan Clutch, available at FCP Groton for about $57.00 + shipping. I too knew it wasn't the radiator, <2 yrs. old and a new thermostat. The only way to tell if its the fan clutch is while the motor is off, try spinning the fan by hand, if it spins easily, then its bad. Mine was pretty easy to tell, b/c while the motor was running, I was actually able to slow the fan down by hand and actually spin it in the opposite direction. I do not recommend doing this. Hope it helps.

Matt
1990 240 DL in OK