177K miles. I've had it for a couple years - has done this the whole time:

Engine temp changes frequently and irregularly. At initial warmup temp comes up to the dot in the middle of the gage. Shortly therafter (5-15 minutes), both in traffic and on the open road, gage rises rather quickly to w/in 1/8"=3/16" of the red zone, stays there for a short time, then drops back down to just below the dot. This cycle repeats irregularly. The higher the ambient temp outside, the closer to the red zone the temp gets. After being on the road for a few hours, the longer the gage stays at the high temp before dropping to mid-range, and remains at mid-range for a shorter time before again going up.

I originally thought that there is an incorrect thermostat in the car and/or it is sticking, but I have been told that there could be something called a temperature compensator board causing the problem. What is a temperature compensator board, how does it function and where do I find it and check it out? Is the coolant temperature actually wandering or is it just the indication?

Thanks.

Most likely the car temp isn't really fluctuating. The temperature compensation board is causing an erroneous signal to reach the gauge. This happens when the board's contacts get old and/or corroded. The contacts just need to be cleaned. My '88 240 had the exact same problem.

1. Remove the instrument binnacle by removing the two gauge blanks (or bezels, if you have gauges there) at the right of the binnacle. Then, remove the knobs from the headlight switch and the dash light rheostat (they pull straight off). Gently pry off the plastic cover on that side. Now, 4 black Phillips screws are exposed. Remove these screws to remove the binnacle. You may also want to remove the plastic cover on top of the steering column. Do this by removing the 2 screws securing it. Pull out the binnacle so that you can reach behind and disconnect all wires. Remember where they go (you may want to write it down).

2. Working on a table, remove the back cover from the binnacle by removing several brass hex-head Phillips screws. Separate the back from the front.

3. When you have separated the back from the front, the temperature compensation board will now be visible. It's on the front side underneath the temp gauge. It's a circuit board about 3" by 3/4". GENTLY slide the board straight off its pin connectors by carefully rocking it back and forth (NOT TOO MUCH).

4. Clean the connector pins, now exposed. I used rubbing alcohol on a swab. Then, lube the pins with petroleum jelly, or something similar.

5. Replace the temp. comp. board on the pins carefully.

6. The rest of installation is the reverse of removal.

Sometimes (rarely) the temp. comp. board itself is bad, but usually it's just the contacts. I fixed my '88 this way over a year ago, and it's been perfect ever since. Gotta love a free fix.

Good luck!

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Guid ('88 244DL 213k, '89 744T 168k, '92 745 164k)

Thanks. Am moving now but in a few weeks when I have my tools again I will fix it. Free fixes are indeed a blessing.

Don't know if your brick has a TCB. However, if you do a search on this site and check the FAQs, there is an abundance of info on how to diagnose/bypass the bugger.

Just my $0.02
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Regards,

David
1991 744 NA 139+K Miles