Do 1990 300SE auxiliary/radiator fans run separately? - PeachParts Mercedes-Benz Forum

francotirador · #1 04-13-2011, 01:00 PM

Hello: I have a 1990 300SE with the M103 engine. I've noticed just the right hand auxiliary/radiator fan running. Should both of them come on at the same time? If not, what triggers them to run individually? I've only observed them with the a/c on, but I'll take a look at them with it off if that makes a difference.
Thank you in advance.

JohnM. · #2 04-13-2011, 01:49 PM

I think that it correct operation, one fan running with AC on. They should both trigger at full speed when coolant temp reaches ~105C.

francotirador · #3 04-13-2011, 02:06 PM

Quote:

Originally Posted by JohnM.

I think that it correct operation, one fan running with AC on. They should both trigger at full speed when coolant temp reaches ~105C.

Thanks for your response.

I've read numerous posts hereon which state different scenarios for the operation of those fans. I recall more than one which stated that one of the fans comes on at 105C and the other at 130C. The 130C obviously seems high though.

I'm trying to figure out if I have something faulty which is causing the temps in my M103 to rise above 100C. I recently put a new OE VDO temperature sensor in the engine. That same day I had also changed the distributor rotor, cap and wires. I also changed the valve and timing cover gaskets.

It may be purely coincidental, but that evening was when I first noticed the engine temp rise above 100C. It had normally hovered around 80C. It seemed that the fan clutch wasn't operating properly, so I put a new Behr clutch in.

The temp hasn't gone as high with the new fan clutch in, but it still goes up to about 105C or so. At that point the right hand auxiliary/radiator fan kicks on and lowers the temp.

I just don't know how much of what I've described is normal.

JohnM. · #4 04-13-2011, 02:23 PM

How about thermostat & radiator?

In what conditions is the engine heating up? If it's when your idling stoplights or stuck in traffic, that's fine. If the temperature is rising above 100 while you are driving along that is an indication that something is not quite right. On a hot summer day sitting at idle in traffic, the engine will quickly heat up to 105C, as long as your aux fans kick on to bring temperature down, this is normal operation of the engine. The fan clutch also engages at around 85-90C to help with keeping engine temperature in check. Anything over 115C should never be observed in normal running. Any measurable time at 120C will pop the head gasket most likely.

francotirador · #5 04-13-2011, 02:31 PM

A new thermostat and hoses are going in this weekend. I'm also going to flush the system. It's a very clean Southern Florida car with only 75k original miles on the clock now. From what I have already observed the coolant system is clean.

The engine heats up during stop and go traffic/red lights.. I haven't seen it go above 100C while driving at a decent pace. I'll do more driving this afternoon to see how it reacts. It has not gone over 110C and certainly never over 120C on my watch.

Thanks once again for your help.

JohnM. · #6 04-13-2011, 02:33 PM

Quote:

Originally Posted by francotirador

The engine heats up during stop and go traffic/red lights.. I haven't seen it go above 100C while driving at a decent pace.

Sounds like its running perfectly normal then. The M103 heats up quickly at idle in stop & go traffic (no air flow, hot coolant). Even a quick stop at the drive-thru will sometimes kick the aux fans on (105C) in the summertime.

francotirador · #7 04-13-2011, 02:46 PM

Well, your last response brings me back to one of my initial concerns. That is, the left auxiliary fan may not be running correctly. If both fans are supposed to run simultaneously, then there's a problem.

Thank you.

JohnM. · #8 04-13-2011, 05:02 PM

Quote:

Originally Posted by francotirador

Well, your last response brings me back to one of my initial concerns. That is, the left auxiliary fan may not be running correctly. If both fans are supposed to run simultaneously, then there's a problem.

Thank you.

Are you observing these fans when the car is at 105C? I think no matter what engine temperature when you have the AC running, one of the aux fans runs...I thought that was your initial observation. If only one of the fans runs at 105C, you can just replace the bad one. Sometimes just spinning the bad fan back and forth by hand will get it going.

Hit Man X · #9 04-13-2011, 07:15 PM

Both of mine run in the 300SEL when the A/C demands for it... sounds like you have a dead fan. Also, install the 79°C thermo in lieu of the 87°C. The car takes much longer to become hot and cools quicker... this makes the fan clutch engage much less often too.

I never have had the temperature high enough for the fans to run on high speed, yet my guess is both would run. I can go jump the switch if you really must know.

My 560 has a bad aux fan.

compu_85 · #10 04-13-2011, 07:30 PM

Ya, you have a dead fan. They are wired together.

-J

francotirador · #11 04-13-2011, 07:39 PM

Thanks to all who replied.

I received some additional info about the operation of the fans from another generous member. As some of you have also stated, it seems they're wired in parallel and should run simultaneously.

I did notice only one aux fan running when the temp got up to 105C. That was the right hand one. I just came back from a little highway/city run with the car. It didn't get over 82C at highway speeds. It also didn't go over 100C in the city. The ambient temperature was about 82F.

Hit Man X · #12 04-14-2011, 10:02 AM

Car's temp will not climb very high on the freeway due to airflow. Mine did not with the 87°C... but as soon as I slowed in the summer, the temp would jump to 100°C pretty quick. Mind you 100°C is not HOT/boiling over by any means, it simply hampers acceleration of the vehicle and heat soaks the A/C condenser more easily.

Due to your climate, run that lower temp thermostat I pointed out previously. The A/C switched on plus a locked fan clutch really makes the M103 work overly hard to propel the 126 around. When I said takes longer for the car to become hot, I mean from ~80-100°C... not the warmup phase. Mine warms up quickly even when we have cold snaps here in the winter.

I really have no idea why MB installed the 87°C in the M103 when everything else I own from them came with the 80°C area units of that area. I can only assume for emissions or something of that nature.

Plus, get out the trusty DVOM and see if you have power to the dead aux fan. If so, it may simply need brushes or a good cleaning to function again. Hell it could simply be unplugged.

francotirador · #13 04-14-2011, 12:01 PM

Quote:

Originally Posted by Hit Man X

Car's temp will not climb very high on the freeway due to airflow. Mine did not with the 87°C... but as soon as I slowed in the summer, the temp would jump to 100°C pretty quick. Mind you 100°C is not HOT/boiling over by any means, it simply hampers acceleration of the vehicle and heat soaks the A/C condenser more easily.

Due to your climate, run that lower temp thermostat I pointed out previously. The A/C switched on plus a locked fan clutch really makes the M103 work overly hard to propel the 126 around. When I said takes longer for the car to become hot, I mean from ~80-100°C... not the warmup phase. Mine warms up quickly even when we have cold snaps here in the winter.

I really have no idea why MB installed the 87°C in the M103 when everything else I own from them came with the 80°C area units of that area. I can only assume for emissions or something of that nature.

Plus, get out the trusty DVOM and see if you have power to the dead aux fan. If so, it may simply need brushes or a good cleaning to function again. Hell it could simply be unplugged.

Thanks for your help.

I recently purchased a new 87C thermostat. I guess I'll have to get the one you recommended now.

I was just going to purchase a new left hand fan as I already have a new one on the shelf for the right side. I just like to install new parts and be done with it.

Cal Learner · #14 04-17-2011, 10:01 AM

franco, you already found out that both fans are designed to operate together, not separately and not singly. As suggested, that means that the inop fan has some sort of problem, either with its motor or with the wiring to that fan. But before replacing the fan, tap on the fan hub with a rubber mallet and see if that might free it up. They sometimes get stuck and that will get it going again. Then again, it may really be a dead motor.

francotirador · #15 04-17-2011, 11:12 AM

I replaced both fans yesterday with good quality new ones.

The one that was acting up did get spinning after I gave it a whirl, but I just don't like temporary fixes. They were 21 years old and they had to go. Overheating is obviously a serious problem that must be dealt with immediately and not temporarily. I replaced the fan clutch and both auxiliary fans this week.

I thank all of you for your responses.