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

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FAQ

W124
Sportline Swaybars
Bilstein HD Struts
16" E420 wheels

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.

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Steve
'93 400E

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.

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

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FAQ

W124
Sportline Swaybars
Bilstein HD Struts
16" E420 wheels

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".

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Regards . . . . JimF
-------------------
'94 S500 Cpe

Visit my Mercedes Web Page

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:

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:fork_off: MB ANTICHRIST:fork_off:

The car does overheat.

I drove around for 45 minutes this weekend, when I got home and parked car to wash it, i saw coolant coming out of the bottom of the car. When i opened hood, it was bubbling over the radiator cap.

Then I started checking fan operation with A/C on and off.

Right now the only way for me to get the high speed stage of the fans to come on, is if i unplug the 2-post connector at thermostat housing...thats it.

FQ

__________________
FAQ

W124
Sportline Swaybars
Bilstein HD Struts
16" E420 wheels

Do you have a proper ratio of coolant to water? Water by itself will boil at 212*F which is 100*C. Adding coolant will raise the boiling point of the mixture overall.

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08 W251 R350
97 W210 E320
91 W124 300E
86 W126 560SEL
85 W126 380SE Silver
85 W126 380SE Cranberry
79 W123 250
78 W123 280E
75 W114 280

Yes. New radiator thermostat and correct mixture, 7,000 miles ago.

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FAQ

W124
Sportline Swaybars
Bilstein HD Struts
16" E420 wheels

TRY THIS YOUNG MAN...REMOVE THE TOP OF THE FUSE BOX COVER (6 SMALL PHILLIPS) LOOK TO THE REAR AND SEEIF YOU CAN FIND A BLUE AND/OR A GREEN CUBE RELAY..( THEY SHOULD HAVE FUSES IN THEM) CHECK THE FUSES AND THEN LET ME KNOW WHAT YOU FIND..???????:fork_off: :fork_off: :fork_off: :fork_off: :fork_off:

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:fork_off: MB ANTICHRIST:fork_off:

He has fan when he removes connector from aux fan thermister, so high fan relay power and fuse circuit are verified. If fan does not come on at 105-107 C , then the termister resistance should be compared to spec. for verification.

Spec for that thermistor is 185 ohms at 100 degrees C. Check it. If out of spec , change it.

I DO BELEIEVE THERE ARE TWO SEPARATE CIRCUITS FOR AUX FAN ACTIVATION. (TWO SEPARATE VOLTAGE SOURCES). THE REMOVAL OF THE SENDING UNIT CONNECTOR ACTIVATES HIGH SPEED FAN AS A DEFAULT.THIS IS THE SAME AS OTHER MID 90'S MB'S(i.e C280)....ONCE AGAIN, ID RECOMMEND CHECKING THE FUSED RELAYS IN THE BACK OF THE FUSE BOX.

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:fork_off: MB ANTICHRIST:fork_off:

COuld be expansion tank cap not holding the required pressure. Should be marked with 140. If it hasn't been replaced it's a cheap precaution either way.

I hear ya.. but .. the schematic for that chassis shows fuse on LOAD side of relay, whereas the coil side of relay comes from thermistor/sensor and even if defaullt was seperate feed , it would still be on relay coil side..so fan has to have a good fuse to run.. No/Bad fuse = no power feed to fan motor.
Again, check aux fan thermistor ohms/temp specs....

Located green colored fuse relay. Opened it up, no fuses inside, just a coil of wire.

I did see aux fan fuse. It looked old, put a new one, I will see what that does.

I unplugged sensor at thermostat housing again, and this time passenger side fan did not spin, until i gave it a spin. Hmmm....

FQ

__________________
FAQ

W124
Sportline Swaybars
Bilstein HD Struts
16" E420 wheels