It was a bad thermostat - PeachParts Mercedes-Benz Forum

rickjordan · #1 02-20-2003, 12:59 PM

I couldn't find my original thread on my temp. problem, so I'll continue with a new one. I replaced the thermostat per several great recommendations from the "collective". With the new thermo. in, the car runs at a solid 95c. Now, I bought this TD in Nov. of 2001, and she always seem to run at 80c, which I took to be normal. I guess all along it was running too cool. The thermostat I put in was a Behr 80c. and I use Mercedes coolant. I was afraid I would break the head off one of the bolts, but I sprayed them with Liquid-Wrench and tapped them with a hammer a couple of times, and they came out. I did have to wirebrush off some rust, but nothing major. For future work, I put some anti-seeze on the threads.
Thanks again to all that pointed me in the right direction.

#2 02-20-2003, 03:10 PM

RIck,

Sounds like you did a good job. There are alot of post which say that the operating temp should be 82 C and that 95C is too high. IF I were you I would leave it alone from now on. 95C is not too hot... I dont think that you will have any trouble with it in the summer time. As long as it does not go into the red no big deal.... What you may want to do is clean the fins in the radiator with a power washer at the car wash when spring comes around. Just remove the radiator and fire away. But even that may not be necessary. I was a fool...... I wanted to run a cool thermostat in the summer and a warmer one in the winter. Not a bad idea but when it involved a broken bolt in the thermostat housing a good idea went bad quick so leave it be so that you can have adaquate heat in the winter time. I dont think that the engine will wear out any faster..... These engines out last the cars anyway.

You did good

BOB C

DieselAddict · #3 02-20-2003, 03:20 PM

95C is where my car operates too and 80C thermostat is the proper one according to the Haynes manual. I think those people who think 80C is normal operating temp have a bad thermostat or sender.

84300DT · #4 02-20-2003, 04:07 PM

great job rick - your symptoms were so exactly like mine i was 99pct sure it was your 'stat.
now you'll be warm and toasty

rickjordan · #5 02-20-2003, 05:13 PM

I took the car on the highway and went about 70 mph and the temp stayed on 95c. The "red zone" is at 120c. The car doesn't take as long as I was used to, to warm up. What confuses me is, doesn't a 80c thermostat mean the car would run at 80c? Hell, I'm not too worried about it. I'll keep an eye on it come summer.
As for cleaning the radiator, this car has a relatively new radiator in it. The previous owner replaced it. Of course a dirty radiator would make her run hotter, wouldn't it? I am just happy the thermostat change went smoothlyand that the car seems to be running better.

rwthomas1 · #6 02-20-2003, 08:20 PM

My 84 runs at 95c all the time. This is with a new 80c t-stat. The temp rating is the temp the t-stat starts to open. It is fully open 10-20 degrees above that temp. RT

JohnM · #7 02-20-2003, 09:04 PM

Because these thermostats are in the water RETURNING back to the engine, your engine should always be above the rated thermostat temperature. An 80c thermostat starts opening at that point and delivers its regulated temperature TO the engine. So you’ll always be above that and if under load, plus whatever span it has until fully open. It’s not like many gas engines where the thermostat is on the water leaving the engine where it is closer to engine temp. Ours see the water (other than the bypass water) after it goes though the radiator.

83 240D

PaulH · #8 02-20-2003, 10:48 PM

Rick, My SDL runs at 90c winter or summer on the open road and 100c in city traffic in 100 degree summer temps. This is with a new t-stat,water pump, and fan clutch.