Hi All,
I have an 83 300D w/200,000. Anyway when I bought the car termostat was stuck open. After replacement the car runs around 85-90C. However after getting off the highway the temps rise to about 98C or so. I suspect the fan clutch, is there any way to test the clutch, and any surprises w/ replacing the thing. Or should I just start playing thermostat roulette ;-)
thanks

For the 617.951 what testing procedure there is, is outined in the engine manual 20-310 . Do you have access to a manual or CD?

Cheap and cheerful test : fan should spin more or less freely when cool. When the temp guage goes up to 98C or so (the next mark on the guage), the fan should spin much faster, more a whole lot more air, and stop within one revolution when you shut the engine off. If it never locks up, replace it.

It doesn't lock up until 100C or 105C, so 98 isn't a problem.

Also check that the electric fan runs on both speeds, too.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Thanks Guys, I don't have access to the proper manual I have a Haynes which isn't all that great, guess I should order the CD. I have popped the hood when the car is cold and when it is at 98c or so and I can't tell any difference in fan speed I'll try the other tests and see what happens. I haven't investigated the electric fan my understanding from lurking here is that the electric fan only goes on with the AC, I'll try that as well. thanks again.
later,
Gregg

Gregg:

The fan should come on with AC and with high temp. On the W124, it has two speeds -- slow with AC and high with temp. The temp sensor is a simple switch -- when you find it (it's on the thermostat housing on the older models), pull the wire and ground it with the ignition on and the fan should run.

Note that the temp guage reading 100 after a highway run is normal. Only a problem if the guage reads near the red zone.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Checking the fan clutch on Diesels is more difficult than on SI engines. Gas engines are quiet enough that you can hear the change in pitch of the air as the fan cuts in. Diesels are another matter.

BTW I've seen more that a few older W123 Diesels that ran right at the 100C mark on the temp gauge. When I check the actual head temp with an infared temp tester the temp of the cylinder head is right in the 80-85C range. I've seen this one my 240D and two 300D's - I'm not sure the temp gauges are gospel - especially since they are two decades old.