I have a 1990 240 DL and I was wondering if a faulty coolant temp sensor could cause plugs to get covered with a black soot. I would think this sensor was only for the gauge on the cluster. I read on a response to a plug fouling problem which led to stalling that the sensor sends signals to the fuel system some how.
Thanks

The gauge sensor is closer to front of engine. The Engine coolant sensor(ECT) is under the #2/3 intake manifold.
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Post Back. That's whats makes this forum work.

I know the location of the sensor. I just wanted to know if this sensor is not working properly... does it cause the spark plugs to foul up?
thanks

Absolutely. That sensor tends to fail rich. In an extreme case, it will turn on the fifth (cold start) fuel injector and flood the car out completely.

I drove a '91 for 300k miles and had to replace that sensor twice in that time. The first one failed the week I bought the car new and was replaced on warranty. The first time it flooded the car out, and I was able to drive to the dealer by unplugging the fifth fuel injector. The second time it just caused a warm restart stall which I puzzled over for years until I happened to replace the sensor while doing a head gasket and the problem went away.

Thanks for the feed back. I'll give it a try and post the results.

If you have a cooking thermometer and an ohm meter, you can test the sensor for coolant temp vs resistance reaction, rather than spring the $'s on a new one that "might" fix the problem.

The temp vs resistance graph is printed in many of the repair manuals, or it may also appear in the 700/900 FAQ's on this site.

Oh, look what I found:

32F (0C)-- about 6000 ohms within a range of +/- 10%
68F(20C) -- about 2300 ohms
104F(40C) -- about 1300 ohms
140F(60C) -- about 600 ohms
176F(80C) -- about 300 ohms
212F -- about 190 ohms

Chris, I never had to play with this.. If you unplug it, does the engine go to Cold start or full temperature mode?
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/

Colder temp equates to higher resistance, so my guess is that unplugging it (infinite resistance) would cause the car to run way rich.

Conversely, (in theory) you should be able to simulate a warm engine by shorting across the two wire lead contacts with a 200ohm resistor, however I'm not absolutely positive and take no responsibility for any negative outcome. ;>)

thanks. just trying digest some info for the future.
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'75 Jeep CJ5 345Hp ChevyPwrd, two motorcycles, '85 Pickup: The '89 Volvo is the newest vehicle I own. it wasn't Volvos safety , it was Longevity that sold me http://home.lyse.net/brox/TonyPage4.html http://cleanflametrap.com/tony/