cooling problems in 96 e300-help!!

[charlie a.]

My 96 e300 temp gauge usually operates at 100 degrees C, lately I noticed that the auxilliary fan does not turn on when the temp gets hot. It will operate for a few seconds then cut off - unlike before when it will keep on for a while. From what I can see, it seems that the switch tells it to turn on but ir just won't as if something is stalling the fan. Can someone tell me if the auxilliary fan is the problem? Or is there a way I can check if this is a faulty switch or sensor ? Or can someone tell me how to diagnose the problem properly?

[TMAllison]

100C seems too warm for normal operating temp. Mine runs at 80-85C generally unless more than 100f outside.

You can check operation of the Aux fans by turning key to pos 2 and then pressing and holding both AUTO buttons on the CCU for 10-15 secs. The fans should engage (pulsing initially is normal) and run at full power. Key off to stop.

If they run you can rule out the elect motors and prob the relay too and move on to sensors.

You can monitor coolant temp while driving using the CCU: hold REST for 5 secs, then using either AUTO button to toggle to screen 6. May read in C or F.

[Matt L]

"operate for a few seconds then cut off" might just mean a starting attempt. In which case, you probably have a bad fan motor. It could also be a bad controller, but this seems to be very rare.

You need that fan. Get it sorted out. Don't install an aftermarket fan unit. It is very important to only use the OEM fan motor for this application.

[charlie a.]

I folllowed your advise and holding both auto buttons in the ccu for 15 seconds, but aux fans did not turn on. Coolant temperature was 83 C. Could this mean that the aux fans are defective or should I start checking relays and switches? Thanks for your help

[charlie a.]

I've checked out aux fans online - they're about $290.00 for a replacement part, I believe the brand is ACM. Do you think this will do? I cannot find an OEM replacement.

[e300D97]

Charlie, If you do get a replacement AUX FAN, they may at first operate backwards. Evidently there was a running change during the 96 model year. Its a very easy fix, you just unsnap the connector on the fan pigtail and reverse the wires and snap back together. Also, just so you know, these temp guages are plateau type, meaning the get up to about 95 and stay there unless the temp exceeds 110 ( I think thats the cutoff) then the temp guage will begin to move higher. Aside from the AUX fans, make sure your fan clutch is working properly. Once the temp exceeds 94, your fan clutch should engage and you will hear it roar as you raise the rpms. I am chasing a similar problem, my 1997 operates at 96-105 when I am commuting home, in stop and go traffic, a few hills with ambient temp 85 degrees plus.etc. I have replaced fan clutch, aux fans, thermostat. I will check once in awhile, while driving the temp via CCA. (hold rest button down for 10 seconds then toggle to 6 using the drivers side AUTO button). I think that even in heavy traffic, it shouldnt go above 96 or 97 , my next step is to clean the fins on the radiator, I havent done that yet, and with 280,000 miles I am sure there is a bit of gunk in there. Good luck and keep us posted.

[charlie a.]

I tried hardwiring my aux fans by jumping it directly to 12v battery and it worked fine. After that I followed Terry's suggestion of doing the CCU test and held both auto buttons for 15 seconds and the fans turned on. Pressed and held the rest button, scrolled to option 20 and it read 10amps.
Once the temperature gets to about 100c, the fans quit and all it does is pulse but not completely rotate.It won't turn on even with the CCU test.At this point if I unplug the fans from the connector and do a continuity test, the test light will only come on once in a while, but not completely stay lit - is this a bad connector problem?
If I jump it again, the fans start and do the whole cycle again. I noticed that once engine cools down, the fans will start again until the temperature gets hot.
Any suggestions?