Thanks for the correction on the third brake light year. Should be easy to remember that no W123 had them.

And I really have the feeling that the 85-mph speedometer thing lasted more than two years.........

And don't start me off on the 55-mph national speed limit........

Ken300D

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1982 300D at 351K miles
1984 300SD at 217K miles
1987 300D at 370K miles

Thanks for the advise, I think I'll change the thermostat and see if that affects the temp. As for the speedo, I think at the time the national mandated speed limit was 55mph and the feds also
mandated that speedo go only to 85. I guess the reasoning was if the speed limit is 55 you don't need a speedometer that goes much above 85. And for those who are wondering, yes a 1981 300SD will go 85 and bury the needle and the engine still runs cool

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Well, I replaced the thermostat and temp sensor. The engine appears to heat up a little faster now and occaisonally it actually reaches 80 degrees.. I guess we can consider this a success.
Tommorrows project, replace the injector return lines. These lines are soaking wet everytime I turn the engine off and I'm getting poor fuel milage. Hopefully replacing these lines will help.

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Did you just replace the two? Did you check the mixture of the fluid in the block (Not the stuff sitting in the tank) to see what % mixture and freeze temp it has?

I tested a truck today that came from *Canada* with a coolant freeze protection point at 12*f (With 2 year old coolant)!

I don't know how to do this?
And since I live in Santa Clara CA. were the temperature rarely get below 40 I'm not to sure it's important.

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A couple of years ago the temp on my '81 300CD started to rise up to between 95 and 100. It had always run at 82-85 before this. I changed out the thermostat and put in fresh MB coolant. The temp dropped down to below 80. I checked the housing at the sensor and got a little higher reading on the laser thermometer. A few weeks ago I changed out the cluster because the speedo went out. Surprise!, my temp is back at 82-85 after warm up. It would seem that my temp gauge was a bit off. I have checked the housing at the temp sensor with a laser thermometer again and found that it also reads around 83 or 84. The moral is don't always trust the gauge.

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Mike

2000 SL500 22,000 miles
1981 300CD 188,000 miles
1979 450 SEL 266,000 miles
2005 Cadillac CTS 25,000 miles

It's not only the freeze temperature that's important. The coolant also prevents the water from boiling by increasing the boiling point higher than 212*f. That way, if you do happen to hit 100*c, your radiator dosen't blow up from the steam pressure. (On Monster Garage with the rock crawler, Jessie gets a 77 caddie and he takes it to the parking lot a redlines it to the point the manifolds are glowing red. It eventualy *blows up* from the water boiling in the system!)