I was driving my 1986 300e on an especially hot day last week. I turned off the radio 'cause there was nothing good on and I heard a strange noise coming from under the hood. It wasn't especially loud or high pitched, it just sounded like a humm or a whirl. It changed as the engine accelerated. I pulled over and checked under the hood. I could swear it was coming from the alternator. The tempature is fine, the oil level is fine and the car seems to be charging. Later that day, after it had cooled down, I decided to drive it home (about 30 miles) It was late in the evening and the weather had cooled down quite a bit. The sound was gone (?) We took it for a quick spin last night and the sound was gone. Today it's kind of warm outside and I took it about 3 miles. The sound was there. It comes and it goes. I asked a friend who's kind of a back yard mechanic and he says the alternator berings might be getting tired or aren't getting properly lubricated on hot days. He admits he doesn't know Mercedes Benz's very well, so I thought I'd ask you guys. Sound familiar?
-Kyle

My guess would be the fan kicking in and out. If it was the alternator the sound would most likely be constant. You may have some belt slipage if this is a clutch fan. Hopefully one of the techs here will clarify.

yal
88 230E (W124)

Fan clicking in and out? Do you mean off and on? This is not that. How do belts sound when they go bad?

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Kyle De Priest
1986 300e
1972 BMW R75/5 (Best there is)

Could be the air pump. Mine makes a whirring noise (mostly at startup)and quite down after a minute or so.

Yal has it right. It's the fan man!!! Well at least you know that's working OK. Alternator bearings are permanently lubed. if they were bad, you'd be hearing their song all the time. Fan does not "click" in and out, but rather engages quietly as the temp of the air coming thru the radiator increases. Your description of the temp situation really points to viscous clutch and fan as making the noise. This is normal. when things cool down a bit, the clutch releases, ergo, the fan becomes quiet.




[This message has been edited by jeffsr (edited 06-19-2000).]