Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help

Go Back   PeachParts Mercedes-Benz Forum > Mercedes-Benz Tech Information and Support > Tech Help

LinkBack Thread Tools Display Modes
Old 11-22-2004, 02:54 PM
junior member
Join Date: Oct 2001
Posts: 592
replaced fan clutch - is new clutch defective?

1986 300sdl fan clutch
the bugger seemed to be running much warmer than the other three diesels in my stable. did flush radiator. and new thermostat. replaced the fan clutch this weekend as per my searching here the fan should stop in a turn or two of shutting off engine. mine spun a lot longer. well new clutch spins quite a bit after warm shut down. and the temperature guage stills reads above 90+ at highway speeds. fan clutch purchased here on fastlane. a behr unit. is this new clutch defective? and by instruction i had the thing positioned vertically for the month or two it was on my work bench. any advice is surely appreciated.

Reply With Quote
Old 11-22-2004, 10:26 PM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Fan clutches are almost never the problem.

They are thermostaically engaged. The likelyhood is that there is a radiator restriction that is keeping an area of the radiator (and thus the fan clutch) cool and not engaged.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
Reply With Quote
Old 11-23-2004, 12:56 AM
Registered User
Join Date: Aug 2001
Location: Evansville, Indiana
Posts: 8,150
The radiator will clog worst in front of the fan since that is where the most cooling takes place.

Do a citric acid flush to see if that helps (although it won't always clear a corroded radiator). If you still run warm, get a new rad, it's a bit cheaper than the new head you will need if it overheats....

If the fan clutch has sticky dirty oil all over it, it's bad -- but a bad fan clutch won't cause trouble on the highway, only in slow traffic. On the highway, running too warm is usually a bad radiator.

1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
Reply With Quote
Old 11-23-2004, 01:25 PM
Registered User
Join Date: Feb 2003
Location: roslyn, LI,NY
Posts: 445
overheating when running

My ol 450sl (1977) also was running hotterwhen driving on highway. First step is changing thermostat . Good luck, cooled things off for me. Abe G
Reply With Quote
Old 11-23-2004, 01:46 PM
SL Owner
Join Date: Sep 2004
Location: East Coast U.S.
Posts: 131

Also, never rely on the temperature gaugues only, shorts and grounding problems cause them to read a higher temperature or inaccurate temperature (happened to me).

On the other hand, your combination of issues does point to the radiator.

However, I'd buy an inexpensive infrared thermometer and shoot it at the water pump and the radiator. Look for cold spots on the radiator (a bit temperature variance), this can help confirm your temp gauge and also help verify the radiator. I bought a RadTech radiator for my 380SL and it was identical to the original one and I think it was made by Behr also (steel, etc)-- cost about $300.
Reply With Quote
Old 11-24-2004, 02:46 PM
Registered User
Join Date: Feb 2001
Location: Colleyville, TX
Posts: 233
I had a similar issue with my 190e a few years ago and culprit was the temp sensor. The aux fan is supposed to come on at 105 and would never come on causing high temperatures in stop & go traffic. I replaced the fan clutch & radiator with no success. Finally after I replaced the $24 sensor everything was fine.

93 400e - with Kumho tires 16 months old (very pleased)
99 Merc Villager
Reply With Quote
Old 07-07-2005, 01:47 PM
Posts: n/a
I posted last week over in Diesel asking why is my new fan clutch not pulling air at temps above 110c. Today I installed yet another new BEHR fan clutch and this too does not seem to function either.

Anyone with any input?

Last edited by BusyBenz; 07-07-2005 at 01:52 PM.
Reply With Quote
Old 07-07-2005, 02:11 PM
Moneypit SEL's Avatar
Now what?
Join Date: Jun 2005
Location: SE PA
Posts: 525
Originally Posted by BusyBenz
I posted last week over in Diesel asking why is my new fan clutch not pulling air at temps above 110c. Today I installed yet another new BEHR fan clutch and this too does not seem to function either.

Anyone with any input?
How are you determining that the fan clutch 'does not seem to function'? It's been my experience that when the original problem stays the same after exchanging a part, then the problem lies in a different area.
1989 300 SEL that mostly works, but needs TLC
Reply With Quote
Old 07-07-2005, 03:38 PM
Posts: n/a

Originally Posted by Moneypit SEL
How are you determining that the fan clutch 'does not seem to function'? It's been my experience that when the original problem stays the same after exchanging a part, then the problem lies in a different area.
Here is my post today from over in diesel discussion:Today I installed the new replacement BEHR fan clutch. No difference in function between the last April's new replacement BEHR fan clutch and this one.

Either I have received yet another defective fan clutch, or temperatures are not getting high enough to engage. Brian Carlton says over 100c and it should begin to engage, or be engaged.

With the A/C on, in drive, I've been able to get it hot enough in order for the aux fan to kick in, 105c, then disconnected the power supply to the aux fan in order to raise the temp even higher, still no action from the fan clutch. In fact, at this elevated temperature, engine running, I can actually stop the fan and clutch with my fingers and hold the fan still.

What is wrong here?

I've spent now $345 for two seemingly defective fan clutches! I'd love for someone to tell me there is for sure something wrong with both fan clutches, but I'm not fully sure!
Reply With Quote
Old 07-07-2005, 05:45 PM
Moneypit SEL's Avatar
Now what?
Join Date: Jun 2005
Location: SE PA
Posts: 525
Does the engine get hot enough to turn the aux. fan on with the A/C off? The auxilary fan will also run when the A/C high-side pressure gets high enough.

Is the engine actually overheating, or are you just going by what the gauge says?

I wouldn't think you should be able to stop the fan with a finger, but I'm not that familiar with MB fans. I know some of the Japanese makes use a fan clutch that freewheels untill it engages. Try that finger trick with a GM or Ford and you could lose a finger.

I suppose it's possible that you've gotten a bad part out of the box. It does happen now and then.
1989 300 SEL that mostly works, but needs TLC
Reply With Quote
Old 07-07-2005, 06:54 PM
Senior Member
Join Date: May 2001
Posts: 104
Read Steve Brotherton's post again. Are the temps in front of the fan clutch at the radiator hot. (too hot to touch). If the radiator is bad it wont get hot enough to engage the clutch.
Reply With Quote
Old 07-07-2005, 08:29 PM
Registered User
Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,804
The problem with diagnosing clutch fan coupling is you can not always use the temp gauge for reference . The temp gauge is sensing coolant temps , not air temps. A bad thermostat will raise hell w/coolant temp, but the ambient air temp at the fan clutch will not even be close to coupling specs.
Same goes for a radiator with dirt/leaves, etc blockage between the rad and condenser . If these are blocking air flow , the clutch never sees this extreme heat at its sensor/pin.
The best way to check temps for a fan clutch is with a IR Temp meter pointed at the viscous sensor area. , not looking at a coolant temp gauge.
I would guess that the biggest mis-diagnosed part of the cooling system is replacing a viscous instead of a thermostat, along with no aux fan operation.
Reply With Quote
Old 07-07-2005, 10:26 PM
PaulH's Avatar
Registered User
Join Date: Dec 2002
Location: Annapolis,Md
Posts: 442
There is a question to be asked. What's wrong with running 90+C on the highway in the summer? I've had my 300SDL since new and it runs 86-90C in the winter and 90-95C in the summer w/o AC on the highway. Add AC and it runs 94-98 on the highway and about 100C in the city. Remember, the aux. fan only kicks in at 105 due to engine heat. (Kicks in sooner for the AC ) MB Engineers must know something. The 603 does run hotter than the 617, probably to reduce emissions. I did replace the fan clutch and the thermostat a couple of years ago, when it was running hot, esp. in city traffic. By the way, my (orig.) owners manual states that the temp will rise "near" the red mark sometimes when driving. Just DON'T let it get into the red portion of the gauge. And, my 18 year old car has a healthy original alum. head and burns 1/3 qt. of oil every 3000 miles - just like it did when it was new. (MB(only!) coolant replaced every 2-3 years. Roteller-T oil changed every 3000 miles.)
Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

Last edited by PaulH; 07-08-2005 at 11:36 PM.
Reply With Quote
Old 07-08-2005, 02:05 PM
Posts: n/a

Originally Posted by gsxr
1) The OM603 FSM has data on how the original clutch should engage... usually when coolant temp is above approx 90-95C. HOWEVER, the replacement clutch (with plastic fan) is from an OM606 and the FSM is silent on engagement temp. I believe it is a higher temp, in search of better MPG and emissions. On my cars, it may not lock up until the dash gauge is in the 100-105C range (or maybe higher).

2) Remember that the clutch is triggered by the temp of the AIR FLOW directly on the face of the clutch. If that area of the radiator (or condenser) has airflow blocked, or if the radiator has a 'cool spot' right there, even a perfect fan clutch WILL NEVER ENGAGE. Many a clutch has been replaced when the real problem was either a bad radiator (not uncommon on the 603 for some reason) or dirty rad/condenser fins.

3) From what is described, I'd bet a 3.5L con rod ( ) that the new clutches are working perfectly, but that it is never 'seeing' hot enough air to engage the clutch. When it's locked and you shut off the motor, the fan stops immediately or within approx 1 revolution, at least both my cars did this when locked. I usually needed the ambient temps to be 95-100F and the dash gauge to be at 100-105C to get it to lock.

4) The vertical storage thing is, IMO, a crock of stuff. New ones are shipped in any direction. I believe this only applies to used clutches.

5) Anyone who thinks the fan doesn't do squat at freeway speeds should remove the fan in the summer and go for a drive at 55-75mph and report back. You may be surprised at the results. (Tip: Bring the fan with you, and the special tools, so you can re-install it on the side of the road.)

6) If the fins are all clean and airflow is normal, I'll almost guarantee the radiator is the problem. An IR thermometer is helpful here, or you can try to feel (carefully!) if the area in front of the fan is blazing hot like it should be with the engine at 100C+.

Thanks for that input GSXR. Yesterday, I removed the radiator, a replacement radiator from about 4 years ago, and blew 100 psi compressed air through the cooling fins of the radiator and while there was no oily gunked on crap restricting air flow, I did see a small amount of sand blow out. Also, I blew air through the AC condenser, also not much came out.

As mentioned, I can hold the aluminum fan still at temperatures at or around 110c according to my dash gauge. I dare not go any higher!

So as far as I can see, this fan clutch does little to nothing since the aux fan will come on at 105c, and it does, and when it does it returns the temp back down to around 85c to 90c. So now I'm wondering, is the fan clutch for the purpose of kicking in only if the aux fan cannot retain, or contain extreme temps. In other words, an auxiliary for the auxiliary, (isn't that an oxymoron?)a back-up for the auxiliary electric fan?
I am not experiencing overheat problems here, but rather implementing avoidance. My cooling system is (with exception of question regarding the fan clutch) the cooling system is 100% with new water pump, thermostat, hoses, aux fan, aux fan thermo sensor, and a recent new radiator, 4 yrs ago.

The OM603 diesel engine with original #14 head, is highly susceptible to cracking due to high heat, such as produced from faulty cooling system components. You need only overheat a 603 with #14 head once and it is toast!

I'm just trying to understand the if I have gotten 2 defective clutch fans, or is there nothing wrong with them. The possibility of blockage in the radiator, directly in front of the clutch fan seems unlikely in my case, so I'm looking for answers? ..................BB

Reply With Quote


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 01:19 PM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Peach Parts or Pelican Parts Website -    DMCA Registered Agent Contact Page