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I've said this so many times I think I'm a broken record: If the gauge temp is above 80C and almost never exceeds 100C, that is NORMAL and don't waste your time or money chasing down a "problem" that doesn't exist.
The thing to look for here is minimum temp of 80C, if it's too low, the problem is most likely a bad t-stat and/or the sender in the head. The senders, when they get old, sometimes read too LOW. A new one is $10, I've replaced them on all my cars as cheap insurance. The other thing is max temp on the gauge under severe conditions - usually the hottest day of summer with A/C on max. Most cars should stay in the 100-105C range here and not get above that. 110C+ may indicate a problem, but regardless the danger zone is 120C+ if your rad cap is ok.
Different engine t-stats (yes, they ARE different for 616, 617, 602, 603, turbo & non-turbo, etc) have different specs. Just because it's rated to BEGIN opening at 80C (like my 603 turbo) does NOT mean the gauge should read 80C! They're usually full open by ~95C, the specs are in your MB service manual - go read it. If your car is running too hot... i.e., 100C+ most of the time, yes there is likely a problem. And yes on the OM61x engines there was a recent discovery by Bruce on the MBZ list that the t-stat housing can corrode and prevent the bypass from sealing off, making the car run hot even with a good rad, t-stat, and fan. Replacement of the housing (~$100) is the proper cure although he did a t-stat modification which also worked.
And of course each car will be different due to a zillion variables. For reference, my W123 with an almost completely new cooling system runs at ~90C year round. Maybe a smidge cooler in winter, but never above 95C in summer, ever. Is 90-95C too hot? NO! IT IS NOT! (deep breath) My one W124 with the new head, and also totally new cooling system, stays parked at 90-95C year round, same deal. I have seen it hit 100C a couple times in 110F ambients or climbing a steep grade, but that's it. Same deal - it's NORMAL. My other 124 has a cracked head/gasket and although most of the time it runs at ~83C, it fluctuates a lot more, popping up to 95-105C at times when it really shouldn't. I don't worry too much because I *know* what the problem is, I just haven't fixed it yet.
In summary: Please don't expect YOUR car to run at 80-85C and freak out if it doesn't. BT, DT, spent the last 5+ years learning this the hard way. Please do change your coolant every 3 years with MB anti-freeze only, make sure the rad cap is good (1.4 bar), and the radiator fins are clean on both sides.
BTW - my post is referring to all MB diesels only, OM61x and OM60x - not gassers.
Regards,
Last edited by gsxr; 03-19-2003 at 04:01 PM.
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