500SL Auxiliary fans - PeachParts Mercedes-Benz Forum

Momo · #1 06-15-2003, 11:26 AM

(I have read all other notes in this forum that refer to the auxiliary fans.)

It's been hot here in the Alps. 35 degrees C/ 95 F. Blasting up the mountains has been great fun. However, yesterday, after a fast blast, with the motor stopped, about a pint of coolant water dripped down under the car. The temperature gauge was just above mid-level at about 105 C/220F. I could hear the water bubbling (boiling?) in the radiator area, and the expansion chamber was completely full. While I am not absolutely certain, I believe the water came entirely out of the expansion overflow. Not had this before.

After topping up, I continued with another fast run. With the temparature guage at the same level, I stopped and looked under the car with the engine running. Bone dry. However, I noted that neither auxiliary fan was running. (The a/c was off) Once I stopped the car, I had another very small overflow. It's a bit cooler today, and I can't get the temperature up that high again, even with the a/c running. All other liquids are at their normal levels. All fuses OK.

My general question is "What should I look at first?". Specifically, I would like to unerstand in what circumstances the auxiliary fans are supposed to work. Should they, for example, like in some cars, continue to work after the engine is stopped?

Suggestions?

Momo

JimF · #2 06-15-2003, 12:53 PM

the radiator pressure cap: probably need to replace it. Shouldn't hear any 'boiling' noises if the pressure cap is working.

Momo · #3 06-15-2003, 03:12 PM

Makes sense to me. Too many years of thermodynamics too many years ago suggest that the water can't boil if the pressure is maintained. I suppose that if a hose somewhere was defective, I would have water coming out elsewhere.

I'll get a new pressure cap tomorrow.

Momo

Momo · #4 06-16-2003, 02:58 PM

Replaced the pressure cap. Inspection of the old one showed that the rubber was in bad shape. I suppose that was the problem. Should be able to tell soon.

Still don't understand in what circumstances the auxiliary fans should come on. Reading other notes suggests that one is for something involving the a/c. What about the other?

Momo

JimF · #5 06-16-2003, 03:19 PM

on by either temp or a/c 'pressure'. Check my page under Menu #18 about halfway down. You'll see a table called Aux Fans Activation that shows at what temp and/or pressure they are supposed to come on.

For example, in a 140 car, the fans should come on LOW [1st] speed at an engine temperature of 100C with no A/C. If A/C is on, then the fans should start if the condensor pressure gets to 14 bar (206 psi) even if the engine temperature is 80C.

They both come on in either mode. Does that answer your question?

Momo · #6 06-17-2003, 01:55 AM

Thanks for the info. I enjoyed reading your informative page. In the absence of other information, I take it that the fans turn off when the ignition is turned off, no matter what the temperature. Is that correct?

Momo

JimF · #7 06-17-2003, 10:44 AM

is not like a Honda! However, I wish it was!

If you let the car set abit after a vigorous drive on a hot day, then start it up, then fans will come on medium (2nd) or high speed(3rd) for a short time.

Momo · #8 06-17-2003, 12:10 PM

Given your proven engineering prowess, perhaps you would like to create another little kit that keeps the fans running after shutdown, if the temperature is above a certain level.

Not sure what sort of physicyst you are. My next-door-neighbor here hired Tim Berners-Lee at the nearby CERN, if you were into that sort of thing.

Thanks again for the advice.

Momo

JimF · #9 06-17-2003, 09:03 PM

but it seems to be a sizeable task! Since the fans would need a constant source of 12V (the battery!), probably a lot of re-wiring would have to occur which would be a no-no.

Even if you could add an 'out-board' unit, it still would need connection to the battery (by whatever means). Also, and this is key, it would have to work in concert with the existing system, since nobody would want to re-wire their cars.

Something to think about however . . . .

Momo · #10 07-17-2003, 02:42 PM

Replaced the radiator cap. With new hot weather, I was up in the Alps again, and discovered that it was not the problem. Oddly, the (boiling) water comes out of the expansion chamber just beside the radiator cap, right where the short plastic vertical tube under the cap joins the expansion chamber. Suppose I will have to change it. Of course, the water that dripped out made the low water light come on when the next person (my wife) drove the car, so now she thinks I need a new one...

Momo