I just replaced the thermostat, fan clutch, water pump & radiator on my 1983 300D Turbo. I drove the car to work this morning & it ran at 80C on the interstate. When I got into town, the temp. went up to 100C at the lights. Outside temp. was 47F. Car runs smoothly. What could cause the temp to go up in traffic with all of the above NEW? I did notice when I replaced the thermostat, it had some brown rust colored film on the stat. I cannot see any oil in the coolant and no coolant in the oil. I am lost as what to do next. Could it be a leaking head gasket? PS I let the car idle for about 30 minutes with the cap off the reservoir tank (to get rid of possible air in the system) after replacing all the above.

Richard

did you recheck to coolant level after your drive?

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Current fleet
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1992 300D - 5speed manual swapped

former members
1984 300D "Blues Mobile"

1978 300CD "El Toro"

I don't think idling will burp the cooling system, and you may still have an air pocket. What was the new t-stat rated for temp. wise?

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1985 300D-189k The 'UD', Ivory and Pinkamino
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A 1994 Ford diesel pickup-349k and
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I've had this problem, I found that getting it up to temp and idle then several vigorous revs gets most (if not all) of the air out of our cars. Make sure the heater is on max doing this as well, I forgot this step last time I did my Honda's coolant and I could still hear the faint sounds of rushing water at times indicating air still in the system.

Did you also use a flushing agent, or simply new coolant/water mix?

I used BERU 80C stat. Did not use a flush. When you rev the engine fast, I am assuming the resevior cap is off?

Yes, it may bubble a little coolant over, but that's fine. If your thermostat was rusty looking it's likely due for a chemical flush, the rest of the cooling system interals are probably a bit gummed up. I'd make sure and do a flush next time you change the coolant.

Seriously elevating the front of the car is cheap and worthwile to eliminate the potential of any trapped air pockets. .If this does not do it removing and inspecting the condition of the water pump might be worthwhile. Usually will just cost the price of a gaket.

No need to replace it unless a problem is found. Personally I think internal wear and failures inside water pumps are not all that common. One still has to know.

Also some way of verification of the coolant temperature has to be done. On the older cast iron heads and blocks if it does not lose coolant in use I would not particualrily worry about it. Running a little hot is better than running too cool.

If you've burped all the air out of the car as previous posters have said and its still overheating then you might suspect a bad fan clutch. My 190E was like this for a while, same with the 420SEL.

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82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Good to pay attention to the fan clutch. Maybe not on a MB, but I had an S10 with a bad fan clutch, and to prove how bad it was it decided to pop off and destroy the radiator.

He already has changed the fan clutch.

when engine stopped use your hands to feel around the rad, see if all the fins are evenly warmed,
my experience was some parts of rad is not hot, it meant some cooling tubing is plugged, so the rad is only partially doing its job.
then u need a new or 2nd hand rad.
I've even put a 300d non turbo rad in a turbo.
if u need to do lots of hill, be prepare to turn on heater inside, atleast it wont cook your engine.

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What you describe as higher temps after a t-stat swap appears to be increasingly common. There have been a few threads on it recently. It may be the t-stats are of lower quality or the bypass function isn't working the same as the older t-stats.

If you have an IR gun, verifying the temp in the cluster would be a good start. Check the connection for the gauge.

With all new parts, I'd expect lower temps than 100 based on an ambient of 47. That assumes the parts are all good, of course.

The t-stat housing is supposed to be self-bleeding, but getting all the air out by elevating the nose is also a common recommendation.

Don't totally trust the dash gage. Is the electric fan turning on? Doesn't it have its own temperature switch, which should be fairly accurate? I'm not expert on M-B's.

I think the electric fan on the older rigs is simply triggered by the pressure in the A/C system, but I'm not 100%. On my 95 there are two fans at the front of the motor, they come on with the A/C on a low speed setting, and then will kick into high speed if the coolant reaches 107c or more.

Electric fan (aux fan) on the W123's is triggered by a temp switch on the receiver dryer. It's not linked in to the coolant temps at all.