My wifes car, 84' 300dt with around 200,000 miles, has just started (yesterday) to overheat badly at idle. When driving on highway the temp is around 85C - 90C with AC on, this is summer in florida so its hot out. When she stops in traffic or drive through the temp jumps to 120C quickly. I haven't looked under the hood yet but does this sound like a problem with the Aux cooling fan not kicking in? And if so, is this an easy fix.

Any help much appreciated

Thanks

yes, and yes.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

The aux fan on these cars is there primarily to improve a/c performance, not to provide air flow to the radiator. I would check the operation of the mechanical fan and clutch before worring about the electric fan. And confirm that the coolant level is correct.

he's right in the sense that the mechanical fan is the primary mover and the aux fan is just that -an auxiliary. In truth, both should be working properly. Idling in hot weather after a high speed run with A/C on does put a high load on the cooling system.

__________________
'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.

Thanks for the answers. The car overheats so dramatically at idle and it runs just fine when moving, (30mph plus), would the air flowing over the engine/radiator when moving cause the very quick heat reduction, 120C down to 90C in less than a minute. Switching the AC off at idle made no difference to the high heat. Could it be the thermostat?

I would replace the thermostat if that doesn't fix it check the radiator, be sure the system hold pressure and the pressure cap is OK.

That engine should run cool!

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

Did this issue with overheating happen suddenly?

Would this vehicle routinely get to 110°C. under similar conditions last summer?

A bit of history of the performance of the vehicle over the past 12 months would be helpful.

I just purchased the car 2 months ago so I don't know its history. The car is in great shape. The overheating problem just started suddenly, my hunch is the main fan, perhaps the clutch. I will check its operation tonight. Otherwise I will change the thermostat, replace pressure cap, and check the radiator (the radiator looks very new).

Did you check the aux fan fuse??

It also has a relay in the fusebox I believe. But definitely check the fuse.
And make sure the coolant level is full.

Danny

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1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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