Okay, my car has always run a little warm since I got it last year. Typically the temp gauge reads about 85-90. Recently I noticed that the water wasn't circulating so I went ahead and replaced the water pump and tested the thermostat by putting it in hot water with a thermometer. The thermostat opened wide at 180. However, after putting it back in, it is decidedly not opening. The radiator lower hose stays ice cold. I would love to say I therefore have the most efficient radiator in the world, but I doubt that's the case. My temp gauge is reading 90-95.

The two possibilities I can come up with are that somehow by heating the thermostat I damaged it, or somewhere in the system (which is supposed to be self-bleeding) there is a huge air bubble preventing the thermostat from contacting enough hot water to open it. Thoughts? I've driven the car approximately 250 miles since replacing the water pump and testing the thermostat. The heat is working just fine.

 

i am looking into purchasing a 1980 300d it supposedly has 83k on the odo and the gentleman says that it over heats, what major issues could it have for it to overhear besides the water pump and thermostat he said the radiator is new? should i bother to take the 3 hour drive?

 

Update: I decided to replace the thermostat just for giggles and seem to have made some progress. Now while idling the car temperature regulates right about 80c but when I drive it goes back up to 90-95. If I stop and let it idle again it will go down to 80c again. The lower radiator hose still stays ice cold. However, I can squeeze it and make the water level change and if I disconnect it from the thermostat housing water gets pumped out of it if I turn on the car so I know that water is definitely circulating through the radiator.

I went ahead and tested the old thermostat in hot water again and it operates just fine.

Damn, this is bugging me. All I can figure is there has to be an air bubble in the system somewhere.

 

my 240 does the same thing 80c at an idle then when driving it reaches the next white line.
seems normal enough to me, although its also like 20 degrees out...

 

mine reaches 80c quick then slowly rises to 100c
and i think the **** that was in it was green when i got it.

 

FI -

previously my temp didn't go over 90 but didn't go back down to 80 at idle. my radiator is clean, new water pump, new thermostat (although it's a 180 not the factory 174) and new fluid. when I took the pump off I also cleaned a ton of grime out of the fan clutch. also, as I said, previously my radiator lower hose would get hot but now it's not. it's almost as if I replaced a bad water pump for a worse one.

 

My 240D runs slightly high at highway speed, I replaced the radiator and t-stat and it did make a difference. Still seems a bit high sometimes (90). I have 2 300SD's the 1985 NEVER goes above 85. The 84 will get to 100 at high speed, I think cause the rear diff is a lower ratio.....

I'm curiouswhy running the MB coolant, not the green stuff is necessary? Are the cooling properties different?

 

I suspect the MB brand lacks silicates (fine particles of glass) as part of its mix. Most off the shelf anti-freezes contain silicates which are very bad for cooling systems with aluminum parts. However, if you read the labels, it's easy enough to find a brand without.

 

Update: ditched the autozone thermostat for the MB part. Both had the same temperature rating but with the MB thermostat the car stays at 80-85 driving around town. However, it still gets up to 90 on the interstate and a little more under load (ie: into the wind).

harumph.

 

I'll do it again next time I take it to hose the salt off. I inspected it with a light behind it and it looks pretty clean. I'm also kind of wondering about the fan clutch.