350 SDL Overheating - Fixed It - PeachParts Mercedes-Benz Forum

ezrider · #1 03-11-2003, 02:38 PM

Original owner 1991, 149K miles.

Was running about 10 degrees C hotter than usual and 15-18+ degrees C over when pulling my motorcycle trailer at 80 MPH.

New thermostat= no change.

New fan clutch= no change.

New cylinder head temperature sender= no change.

Replaced original radiator and water pump with MB new radiator and MB rebuilt water pump. Now runs normal (a little over 80 C) again. About 86C when pulling trailer at 80 MPH.

Water pump was rough to turn and leaking slightly when taken off.

gsxr · #2 03-11-2003, 02:56 PM

Congrats on fixing it! That's one more success to add to the list... almost every OM60x engine I know of that ran hot was cured with either a new radiator or fan clutch, or both. Temps up to ~100C in blazing summer heat is normal, but more than ~105C usually indicates a problem. Mine run at 85-95C almost all the time, summer and winter...

Regards,

ezrider · #3 03-11-2003, 03:35 PM

gsxr,

Mine never ran over 90C until about a year ago.

gsxr · #4 03-11-2003, 03:50 PM

That's excellent. But I've also seen cars that run 90-95C with a new head, radiator, clutch, water pump, coolant, t-stat, and rad cap. It would not go over 100C but was never under 90C. I just don't want people chasing a "problem" that isn't a problem.

Your case is a little different - yours ran under 90C for years and then suddenly went up 10-18C, which was obviously not normal for YOUR car. Luckily you fixed it before summer, so you can sleep well now! :p :p

Regards,

ezrider · #5 03-11-2003, 04:36 PM

Dave M,

I would suspect that a variance in the actual accuracy of the in car temp gauge could be part of the picture as well?

gsxr · #6 03-11-2003, 05:06 PM

Yes - you are correct! This is usually - but not always - the sender in the cylinder head. It seems the older senders (15+ years) can start reading LOW, and a new sender ($10) brings it back to normal. I had this happen on my '84 300D. Annoyingly, Mercedes has no published temperature vs resistance curve for that particular sender, so it's difficult to test it with a meter. Luckily it's cheap enough to just replace and ignore for the next 10+ years. I put new ones on my other cars just to be safe.