88 420 SEL After driving in traffic, when it becomes stop and go the temp guage goes up from 80 to about 95.. Once I get going again, the temp comes down. Is there anyway to "force" the radiator fan on ?

Thanks

I would say check the fan clutch. If it's free spinning, that's you're problem. It's simply not pulling enough air through the radiator when you are at a stop.

It's perfectly normal behavior. The engine driven fan thermoclutch doesn't tighten until about 100C and the electric engages at 105C.

If you run the AC the temperature might run a little cooler because the electric fan engages periodically at low speed based on AC system demand.

The normal operating temperature range is 80-105C. If it stays in this range, there is nothing to "fix".

Duke

I'd 2nd your fan clutch. My M117/116's all stay in the 80-90 mark.. 90 is acheived after hard running hard, hitting major traffic and sitting w/ the AC on.

I was driving around in a 420 that acts Exactly as you described and when I checked his fan clutch is was spent.

Jonathan

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Jonathan Hodgman
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Enthusiast Service, Restoration & Tuning.
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I'll second Duke, if it ain't broke don't fix it.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician

My 89 420 SEL runs at about 85 to 90. In heavy highway stop and go traffic, it reaches 100. I have had no need to turn on the AC this year, so I'm not sure how it will read with AC.

I just put in a new thermostat(behr), and a new water pump (Mercedes), new coolant and last year, a new clutch on the fan. Before the thermostat and water pump change, it use to run at 80, and only around 70 in the winter. Sometimes only 65 in winter, even after a highway run, but the outside temp was -28c.

I changed the clutch last year because it use to go up to 90, on the highway, under heavy load going up a big hill, travelling at 100-120 KPH. Normally it ran at 80 on the highway. Also, when idling in summer, the temp would rise to 105 and then the electric fan would come on. My analysis was the clutch was slipping. After the clutch was replaced, when idling, no AC, the temp always stayed below 100, and never did the electric fan come on.

Your readings look normal to me.

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1989 420 SEL