That does sound too hot, my 300D (with a new radiator stays between 85-95C in 90-100F temperatures with the AC running. It will only reach 100+C if I climb a very long steep hill at highway speeds, then it cools down immediately on the downhill drive.

I don't know what the "tiny pieces of orange" are but it does sound like you need a cooling system flush. You may also have some air trapped in the system. Some times disconnecting the upper radiator hose and filling through there helps. Also, try running the heat for a little while to remove any air from the heater core. It will probably be easier to flush it first, them worry about the air when you refill the system. Don't worry about the "extra" gasket, it's probably for another application. If none of this helps, you can try reinstalling the old thermostat.

run car @ 2000 rpms with defrost heat on high until you see a dramatic reduction in temp reading should just take a few minutes, to bleed air out of system. if it got up around 120 i would be getting cautious. this is per mercedes mechanic who has all the certificates and he said this is what is recommended

i had replaced a bunch of parts and found out it was a bad temp gauge.

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Brian

82 300d turbo 164k - passed on
83 sd - passed on
04 civic hybrid - DD
06 GTO for sale - passed on
84 VW Rabbit Diesel 4dr.- passed on
94 S350D - DD
94 S320 - soon to be DD

Will try the heater and adding through the upper hose. When I removed the old t-stat, it was a bit rusty in there or the water was a bit on the orange/rusty side. Of course, I threw out the old t-stat and garbage was picked up today. I will let you know if those things change the situation. I know some guy suggested that I boil the t-stat first to make sure it functioned properly and I didn't do that. Don't know if that's it or not, but will try this other stuff first and post results. Thanks! Lance

Well, if the coolant looked rusty that's an indication you should flush the system too. I'm assuming you gauge was reading OK before? BTW, did you install an OEM thermostat?

The gauge was reading fine before. And the thermostat was a Behr, exactly like the one I replaced. I just spoke to my neighbor who said it was unnecessary to replace that part. Who knew?

After having been home for about an hour and a half, 2 hours, I opened the reservoir again and more air came out, like opening a soda.

Where is this air going to escape from if I leave the reservoir cap on?

The reservoir is the high point of the system and should be half full of air, when the engine heats up the air should be pressurized up to the pressure rating of the cap. If there is excess air in the system it should eventually find it's way to the reservoir, resulting in a lower level. If the system stays pressurized overnight, you need to start considering a head gasket problem.

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Just out of curiosity, what were your temps before you did the work?

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1981 240d
Newport,RI

Lance,

Those temps are too hot.

Based on the work you did to the car, there are only two (maybe 3) possibilities: 1) air bubbles trapped in the system or 2) a bad thermostat. Also, did you make sure that the arrow on the new thermostat was pointing up?

I am assuming that your temp readings were around 90 C before the work you did. (please confirm).

As per the FSM: run the system at intermittent operation (with the heater on defrost the whole time) from a cold start up to ~60 C with the radiator cap off. Then put the cap on. It is a self burping system and should require no special manipulation to get air bubbles out.

The orange bits are probably rust, and it would suggest a full coolant flush and descale-ing.

The extra o-ring (the smaller one) that came with the behr t-stat was for use in a different car.

I know it seems crazy that a new thermostat would be defective, but it is alarmingly common. I recently went through the entire cooling system on my 84 300TD trying to track down the source of my 100 C operating temp and it turned out to be the new t-stat (ironically the one that was in the car when I bought it was the same way). The full story is in this thread: Troubleshoot a 617.952 cooling system (84 300TD turbo)


One more thing, what is the pressure rating on the new expansion tank cap you installed? It should be printed on the cap (e.g. 120).

Craig, How can you tell if it has a head gasket issue? After the radiator broke, I did get some steam but turned off the a/c and pulled over ASAP. I was able to reclamp to the old radiator and fill with water and the temp was perfectly fine after that. It did run hot for a few minutes, though. I had a busted head gasket on a '95 E320 I had but that was a very dramatic event.