This morning on the way to work the temp gauge was fluctuating quite rapidly between 110 and 80 (1985 TD - 207,000). With the change in engine temp was a cooresponding change in cabin temp. When the engine got hotter, the cabin got cooler. I seached and did not find this specific problem. I am thinking thermastat and not climate control. Is it possible for the t-stat to close and not allow enough hot coolant to the mixing valve?

Any help is appreciated. This is my daily driver and it is starting to get cold here in New Jersey. If I need parts, the MB dealer is five minutes from the office and I can repair tonight.

__________________
Paul

1991 300TE (280,000)
1985 300TD (432,000 miles - retired)
1976 300D (225,000 - retired)
1975 300D (165,000 - retired)

Most likely your thermostat is going bad. They usually fail in the open position but when mine went the temp went all over the place for a while. Thermostats seem to fail more often when it's cold out as the radiator is very efficent so it forces the thermostat to open and close a lot more often. If you can get away with it, it's not a bad idea to test the new thermostat in an old pot full of water on the stove before you install it as there have been a bunch of bad, new ones out there.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

It is lunchtime and I had a chance to look under the hood. Actually under the car too. There is a wet spot and dripping from the center pully - looks like the water pump. I will change that and the t-stat. Anything else while I have it apart? Anything out of the ordinary (hidden bolts, etc.) to get this fixed?

__________________
Paul

1991 300TE (280,000)
1985 300TD (432,000 miles - retired)
1976 300D (225,000 - retired)
1975 300D (165,000 - retired)

If my memory serves me correctly there is a section of hose behind the water pump that can only be replaced by removing the pump. If that's the case on your car then I'd replace that hose while you're at it. Your parts guy can tell you for sure if you have that hose section. Be sure to put some antisieze compound on the bolts for the pump and be prepared for the old ones to come out a bit hard.

__________________
LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold

Changed the water pump and t-stat in the parking lot a work on Monday night. Fairly easy job (except for the darkness). All bolts came out easy and everything went back together with minimal problems. Only glitch was the alternator adjustment was STIFF.

Car runs great again with steady temp at 90. I will be changing the mono-valve over the weekend as a precaution.

Thanks for the help.

__________________
Paul

1991 300TE (280,000)
1985 300TD (432,000 miles - retired)
1976 300D (225,000 - retired)
1975 300D (165,000 - retired)

High temp + no heat = low coolant level.

The first time I saw this was on my '79 300D. Ever since, whenever I get low heat levels on any of my MBs, I know to check the coolant level. Topping it off always worked.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)