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1984 euro 500sec
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110 Posts
Discussion Starter · #1 ·
With the engine off is the fan supposed to spin more freely when its at operating temp than when cold? If so how/when does it work?
 

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Depends on the day!
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13,337 Posts
that fan should get tighter the warmer the car..ie the hotter things are the more air you want to be moved over the engine.

If it spins w/ equal resistance both hot and cold you know it's shot.. Typically the most common sign of a shot fan clutch is a car who's temp is fine while driving but once you come to a stop it rises quite quickly.

Jonathan
 

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84 380se
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64 Posts
Hmm. Fan clutch.

jhodg5ck said:
that fan should get tighter the warmer the car..ie the hotter things are the more air you want to be moved over the engine.

If it spins w/ equal resistance both hot and cold you know it's shot.. Typically the most common sign of a shot fan clutch is a car who's temp is fine while driving but once you come to a stop it rises quite quickly.

Jonathan
Would it also *fail* to cool down once high? I've been chasing a cooling problem for the past 2 months as it gets steadily hotter down here in AZ. I can see the temp jump as the thermostat opens, but it keeps creeping up, and even when I go back to steady driving at 40+ mph the temp won't dip back down below 100 to 105. This is with the aux fan running all the time, and with a recent tstat and cooling system purge. This is irregardless of outside temp. Its been 60 degrees or its been 100 degrees, and the temp still does the same sort of spike.

I was thinking scaled radiator or bad water pump or fan clutch, and the clutch seems to have the same amount of spin cold before I drive, as well as the same amount after its at running (or higher) temp. Since I don't want to guess at $250.00 or so to replace the clutch, do you know of a spacer (like the flex-a-lite fans use) that I can use to replace the clutch and see if the symptoms change? It can't be that expensive for a fan clutch bypass block as it is to play "Guess the broken part"

Glenn
 

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1984 euro 500sec
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110 Posts
Discussion Starter · #4 ·
well i just bought a brand new clutch for my car but its just as bad as the old one, i think it must be faulty, it gets easyer to turn the warmer it gets
 

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89 560sec, 83 300sd turbo
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435 Posts
Something surely wrong there I would return that puppy as defective. It should be harder to turn as it gets hotter. It will never be hard just more firm then when cold. Usually if the car continues to run hot when cruising, it is not a fan clutch issue as there is plenty of air flow while you are moving.
 

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fan

It is correct for the fan to spin freeer when hot since the silicone is not a viscous when hot. Look in your engine book and you will see a port in the fan housing. To see if that port opens get the engine REAL hot and see if the fan "roars" when you rev the engine. If it does then it is engaged.
 

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300 SEL (1989)
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369 Posts
Experienced similar problems.
Hiway driving temperature just above 80 C
Town driving 90 C --> 100 C
Engine stopped - temperature climbes - 100 C --> 110 C+ & viscous fan freewheels.
Changed the fan clutch - temperature just below 80 C; very high air noise.
Everything seem OK for now.
 

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1984 euro 500sec
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110 Posts
Discussion Starter · #8 ·
So with your new fan clutch its now harder to turn when the engine is warm?
 

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83 300 d t
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699 Posts
100 c is not over heating i would check eletric fan this should come on when you turn ac on or car reaches 100c if it not i would think the auxilary fan is more likely your problem . may be the brushes in electric fan are bad and when fan gets hot it stops
 

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Try the cool harness - especially in AZ/CA/NV

Check the other post for the "cool harness" - which in-line cuts in the auxilary fans at 85C - which will keep your engine overall better/cooler especially in heat demanding enviorments - works great !! That guy deserves every few bucks he made figuring the values out for that one - a great CA 140/126 guy...
 

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'80 450SLC Afro RHD Ikonengold
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3,153 Posts
On older type centrifugal clutch fan, while engine off, the free spin was somewhat easer on warm than on colb but surely clutch worked in funny way: fan was disconnecting on revs over 3800rpm and on fully stopped engine. Thus on low revs and high heat the engine would rise temp up to 100^C but never more and a few min after more than near idle revs the temp would go down.

On visco clutch, the disconnecting/connecting point is determined by water/housing temperature (and later with electro clutch) and in case of high engine temp usualy the clutch was the culprit. However, I've seen a faulty termostat causing high temp too (on 4.5l M117985).

I am not sure how good is to have aux fan to operate at 85^C (87^C is nominal engine temperature). somewhere ~100^C is good for trafic congestion when main fan is creating just below enough of airdraft to keep it ~ nominal temp. Maybe for hoter areas ~90^C would be the best option otherwise, aux fan @ 85^C may create situation that main fan seldom operates fully engaged thus inducing premature aux fan failure.

Just my theoretical oppinion.
 

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Cool Harness is not a theory - you can live with it

No theory - basic fact is the temp aux switch/resistor value for 126 was determined by Germany - same for all parts of the world - and summer's in Germany are not as long or hot as the more temperate zones in the world.

That enthusiast was smart, and analytical, and running cool harness has never hurt me in 5-6 yrs use in S Cal and Nevada.... check out his link in the other post - don't be put off by his prodigy address... other thoughtful helpful comments stuff.... I might be wrong on the exact new cutin temp, check his site he picked a thoughtful cutin temp.

In places like SoCal including Palm Springs and Las Vegas...keeps the engine cooler.

In some desert's (like Iraq) most of the older MB's have the fans direct wired - when the car is on the auz fans are on.... but I am not moving there...
 

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1991 300SE
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tucson_sailors said:
Would it also *fail* to cool down once high? I've been chasing a cooling problem for the past 2 months as it gets steadily hotter down here in AZ. I can see the temp jump as the thermostat opens, but it keeps creeping up, and even when I go back to steady driving at 40+ mph the temp won't dip back down below 100 to 105. This is with the aux fan running all the time, and with a recent tstat and cooling system purge. This is irregardless of outside temp. Its been 60 degrees or its been 100 degrees, and the temp still does the same sort of spike.

I was thinking scaled radiator or bad water pump or fan clutch, and the clutch seems to have the same amount of spin cold before I drive, as well as the same amount after its at running (or higher) temp. Since I don't want to guess at $250.00 or so to replace the clutch, do you know of a spacer (like the flex-a-lite fans use) that I can use to replace the clutch and see if the symptoms change? It can't be that expensive for a fan clutch bypass block as it is to play "Guess the broken part"

Glenn
Damn Glenn. That sucks that you 're still having problems with the cooling system. So you did replace the t-stat and purged the system? From this point I wonder if the pump is the culprit?
 

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2024 SL770
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Fan clutch and radiator are the most likely culprits. The w126 V8 cooling system is notorious for being adequate and no more. If either item is not up to snuff, overheating can be a problem, especially in our neck of the woods. Thermostat is an easy, inexpensive experiment, but it's an unlikely candidate......
 

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1988 Mercedes Benz 420SEL 258,000 miles (SOLD) 1991 300se 168,000 miles, ASR 1999 GMC Yukon 192,000
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i have no overheating problems or idle issues just a constant fan roar at all times unless under very hard acceleration ie 3700-4500rpm but it will continue after the shift? could this be a shot fan clutch?
 

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i have no overheating problems or idle issues just a constant fan roar at all times unless under very hard acceleration ie 3700-4500rpm but it will continue after the shift? could this be a shot fan clutch?
Yes it IS a problem. If it is engaged when cold you are wasting gas. If so suspect that the bimetallic valve is stuck on.
 

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'82 Euro 500SEL, '85 Euro 500SEC AMG WB Cabriolet,'86 Euro 500SEC RUF
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900$SEL,
Are you sure it's your viscous fan or your Auxiliary fans running all the time. They sound like a jet engine. Never heard the Viscous fan sound like that.
The Auxiliary fans come on near 100 C if turning on and off correctly.
If they are running all the time I think there is a temp switch at fault.
 

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1987 420SEL
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1,133 Posts
I would be interested to know if there is a way to open the clutch itself and rebuild it. I never really looked at mine when it was out.
 

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1988 Mercedes Benz 420SEL 258,000 miles (SOLD) 1991 300se 168,000 miles, ASR 1999 GMC Yukon 192,000
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1,376 Posts
my first question would be were is the bimetallic valve located? and to chadahar could it be the aux fan? iv reved it while staring at the front of the car and the aux fan does not move, though it makes the same constant blowing noise that i hear when running the car...
 

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1983 300SD (90K), 1985 300CDT (69K) brand new, 1970 250C, 1989 190D (45K) brand new
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164 Posts
I just changed the fan clutch on both the 123 and the 126. I cring at the cost of those blasted devices. Anyhow, the 123 replacement has worked out well. Even in hot AZ the temp guage does not creep far from about the 80C mark.

The 126 I'm really sorry I spent the money on the fan clutch. No change in the temp. That is, the temp often swings up to 100, down to 85 and back when ever it feels like it - depending on driving speed, etc. And yes, I have done a flush and change the T-stat.

After reviewing the situation, I realized that the fan does not sit inside the shroud. So now I'm thinking that the air is not being pulled through the radiator like it sould. Now I wish I had spent that fan clutch money on a electic fan instead. Instead, I need to fifure out how to extend the shroud to reach the fan.
 
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