1991 300SL - Overheating - PeachParts Mercedes-Benz Forum

brownie · #1 08-22-2006, 03:04 PM

I have a 1991 300SL that I just purchased. The car seems to have an overheating problem. Before I purchased the car I let it idle for along time and I ran it pretty hard to make sure that it wouldn't overheat (no overheating). The temperature never went above 80. The coolant fluid sensor light came on and I opened up the resevoir and filled it up. Now ever since I did that it runs during driving with AC on about 80 to 90 and at idle with the AC on somethimes goes to 110 and 115 even up to the 120 mark before the red. I asked a mechanic that repairs european cars and he tells me that this car doesn't have a coolant bleeder screw and that it self bleeds. Is that correct. I believe there is some kind of coolant bleeder screw somewhere on the coolant system but I cant find it. I also changed the thermostat with a Mercedes part and had the system flushed. Still over heats (never reaches the red). I also thought it could be the fan clutch. Any suggestions will help

Thanks

waybomb · #2 08-22-2006, 05:38 PM

When it gets around 100c, do the aux electric fans turn on?

SunGuy · #3 08-22-2006, 06:30 PM

Hey Brownie,
Did you replace the antifreeze mix with MB Fluid or Zerex G05 (equivalant I think) after you flushed the radiator? Also, in the parts you replaced I didn't see Pressure Cap; sometimes even on these cars it's something simple. Last, if the aux fan does not come on as the other post indicated to check, in my case it was the ceramic resistor that dries out and fails, breaking contact from the temp sending unit to the fan. Good Luck, post how you make out-

Bob

tecqboy · #4 08-22-2006, 08:56 PM

There is quite a bit of info on this forum about overheating and the viscous fan clutch. Do a search. The fan clutch failure is a common and known issue.

Red SL · #5 08-23-2006, 07:21 AM

Temp gauge at 120C-but no clue! Help,
was posted a few days ago; do a search lots of good information on this issue.

Gary Ganaway · #6 08-23-2006, 06:48 PM

I posted this thread about 120 degrees and no clue. Easy try is the expansion tank cap..did not help me but many times this is the solution and it is a cheap solution. Next as far as easy to do would be the water temp sender located on top of engine..a single pole sender unit about $20 or so. My car was not boiling over or was the aux fans coming on but the temp gauge went up to about 120 so I believe this was my problem but not sure since I also put in new thermostat. this job was somewhat of a bit..h so I would try the temp sender first then the t stat. In any event for about 60-70 $ I fixed the problem and do noat feel bad about putting in un needed parts since t stat and cap are usually normal maint. anyhow.