If I remember correctly, way back when I had my 1984 Jetta diesel, I replaced the thermostat with one that opened sooner, thereby allowing the engine to run cooler. Does such a replacement thermostat exist for the M103 engine?

I suspect some after-market producer makes one, but the original 87 degree celsius is what was intended for the 103 motor. A cooler t-stat can sludge an engine.

If it's running hot, the cause will need to be determined. Perhaps the existing one is tired or you have air in the system. This is a common problem on 103 motors along with a long list of other possibilities.

The SEARCH facility will bring up all of these.

No cooling problems, at the moment. But then again, it is winter and the temps have been between the 40s-60s F. The car has been running a needle width below the top of the 8 on the 80C marker. You can just see the top of the 8 without seeing the black inside the upper 8 loop. Normal, from what I gather. I was able to get over 200K miles on those little 1.6 Litre VW diesels with the cooler thermostat and was just wondering if something similar was available for the M103.

Even if it does exist, do not use it.

__________________
Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record

Had similar problem with a '90 M104. First, be careful with lowering temp as it could affect emissions(87C is ideal). Second, my engine would go 100C+ in the summer months until I did the resistor trick (search here for resistor+temperature, should get it) which kicks on the electric fans earlier. It will now control at approx. 93 deg. C

If you're needle is just under the 80, you're already running too cool, then again, who knows for sure what the REAL temp is.

It's not at all unusual to see these motors at 87-90 in the summer while underway, especially with the A/C on. At idle in summer-like conditions, 100-105 is also not unusual.

Cars were designed to run hot; there's a fine line between hot and too hot.

Stick with an OEM 87 t-stat.

Your car is running right where it should be. Remember that the aux fans don't kick in until you're well over 100 degrees, and that's the way they're designed to operate.

-anthony