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Old 04-08-2008, 11:23 PM
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1985 300D running hot

I've got a 1985 300D which is running at about 110C which is pretty hot for winter. When we run the heater it runs about 10 degrees cooler. Any idea where I should start first? I'm thinking radiator since it runs cooler with the heater going.

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Old 04-08-2008, 11:31 PM
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How many kms on the car? Water pump may need to be looked at.
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Old 04-08-2008, 11:35 PM
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Originally Posted by 85300DT View Post
How many kms on the car? Water pump may need to be looked at.
It's got 207K on the car. We just bought it and it's in mint condition besides this problem.
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Old 04-09-2008, 12:15 AM
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Likely to be the thermostat. Radiator and water pump are other possiblities, but the thermostat is less expensive and easy to change, so I'd do that first. The fan clutch is another possibility. Under what conditions does it run hot?
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

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Old 04-09-2008, 12:17 AM
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I've got an 1982 300d that I've had the radiator rodded out, replaced the thermo fan, replaced the thermostat, looks like I should have started at the water pump.
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Old 04-09-2008, 01:22 AM
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Lets start with first things first--check that the car has enough coolant...

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Old 04-09-2008, 06:52 AM
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I agree to check water, I agree that if it were stat the heater would have no effect.

First try cleaning the external fins of the radiator with air and water blowing from back to front.

Cleaning it professionally may not work since there is not much metal in the fins to work with.

Self flushing with the popular flush may do it too.

It could be the fan should have resistance to turn when stopped and not wobble.

Tom W
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.
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Old 04-09-2008, 08:04 AM
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Try a citric acid flush. Do a search for citric acid flush and follow the directions.

I would also think about replacing the radiator as it is over twenty years old and is probably clogged. You can get a replacement Behr from for about $200.00 When I did the flush, it loosened up the clog that had blocked a hole in the rad... Replacing it is at most a 1/2 hour job.

It made a big difference in the 300SD took the temps from 100+ to 85

Make sure that you fill the system with Zerex G-05 and only to a 50% ratio. Any more antifreeze and the temps will go up due to the Zerex's lower ability to transfer heat.

Make sure that you 'burp' the system as well... park on an incline with the radiator facing uphill, get it up to operating temperature, turn on the defroster and gun it up to 3000RPM a few times. that should get any air out of the system.

Good Luck!

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