W124 aux fan issue.....I read tons of posts - PeachParts Mercedes-Benz Forum

Q-Ball · #1 08-20-2006, 10:03 PM

Been a while since I have posted, been restoring a BMW 2002 for autocross this past year.

I know you guys have the answer.

1993 W124 165K. Perfect condition, everything done to it. I may drive this car 2k a year now, was daily driver for a decade.

Problem--At start up, aux. fans no longer operate, which they are supposed to for a short while. Once vehicle idles for a while, temp. goes up, and high speed fans will not come on at 100-107 mark. If I turn on A/C, both fans kick on. If i unplug 2-post, blue switch on thermostat housing...high speed aux fans kick on...i plug it back in and the fans shut off.

What am i up against? I have spare fans to replace the others. Should i be concerned over an electrical issue, at thermostat? O rjust pop in new fans.

Thanks again everyone.

FQ

400E · #2 08-20-2006, 11:42 PM

Quote:

Originally Posted by Q-Ball

Problem--At start up, aux. fans no longer operate, which they are supposed to for a short while.

Not true! Aux fans are not supposed to operate "for a short while" at start up.

The fact that they come on with AC, and when coolant temp switch is unplugged, but not with high coolant temps, suggests a bad coolant temp switch.

Might want to check out some more old posts.

Arthur Dalton · #3 08-21-2006, 01:13 AM

High fan does not start until coolant temp of 107 is reached.
Unpluging sensor simply defaults fan circuit and verifies operation.
I believe you are just short of cut-in temp.

Q-Ball · #4 08-21-2006, 08:43 AM

I recall in previous years the fans coming on during start up. This is an M104 motor, is this not correct?

If i let the car idle currently in the florida heat, the temp will rise, and i have coolant bubling over in the tank. The high speed fans are not coming on at all, unless I unplug the sensor at the thermostat housing. After this occurred yesterday, as a test, i noticed the upper radiator hose had sucked in. To get air back in, I loosened the cap on the coolant tank.

Where is the coolant temperature sensor?

Thanks

Fq

JimF · #5 08-21-2006, 10:48 AM

Quote:

Originally Posted by Q-Ball

I recall in previous years the fans coming on during start up. This is an M104 motor, is this not correct?

If i let the car idle currently in the florida heat, the temp will rise, and i have coolant bubling over in the tank. The high speed fans are not coming on at all, unless I unplug the sensor at the thermostat housing. After this occurred yesterday, as a test, i noticed the upper radiator hose had sucked in. To get air back in, I loosened the cap on the coolant tank.

Where is the coolant temperature sensor?

The fans are supposed to come on at (around) 100C w/ the A/C "off". 107C is a bit high but I've seen a few cars that kick-in at the temp.

If it's a HOT day (90F) and you start the car w/ A/C "ON", the aux fans will come on when the pressure reaches around 14 bar or 206psi. For example, my fans come on at 15bar, apx 240psi. Check MENU#18 about in the middle of the section; the table shows the pressure and temperature kick points for an S car. Yours is similar except you don't have the number of stages (3) that the "S" has.

If the weather is cool, the fans will not come on even w/ A/C on if the pressure is not exceeded. Here in So Cal, my fans don't come at all even on an 80F day for normal driving until the PSI or TEMP is exceeded.

If you want to turn them on at a lower temp, check out my page and the "Cool Harness".

CAPT POUNDCAKE! · #6 08-21-2006, 10:56 AM

you have nothing wrong with your fans...if the car isnt overheating and the a/c is functioning correctly,then just drive and enjoy:fork_off: