Comments on: M117 Auxiliary fan cut-in modification

By: admin

admin — Fri, 08 Aug 2025 04:55:45 +0000

In reply to Jeff. Yes that is the idea. the resistor changes the kick in temperature. You don't want it too low or you're just fighting with the thermostat.

By: Jeff

Jeff — Mon, 04 Aug 2025 15:07:32 +0000

In reply to admin. i see, so when you connect it to a 1100ohm resistor and it did lowers the kick in temperature than before? h

By: admin

admin — Mon, 04 Aug 2025 05:48:01 +0000

In reply to jeff. I understand it to be a resistor, but it's easy to check if you just bridge the pins, the fan should kick in if everything is working.

By: jeff

jeff — Mon, 04 Aug 2025 04:32:01 +0000

Hi, got a question, on my 560sl i saw exactly the same 3pin green top temperature sensor, just wondering for the add up of resistor, is this sensor as variable resistor that change with temperature? or just a open-close switch that trigger at certain temperature, I’m confused because when car is at 90 degree, I measaure the resistance between 2 port but it shows infinity, and I do connect a 470 ohm resistor, in theory at 90 degree with 470 ohm resistor it should trigger the fan on, but it didn’t. And the fan is functional, it is working for ac at stage1 speed, and when short that 2pin connector it trigger stage 2 fan speed.

By: W126 auxiliary fan replacement « Classic Jalopy

W126 auxiliary fan replacement « Classic Jalopy — Sun, 15 Sep 2024 12:13:08 +0000

[…] I’ve had to do quite a bit of work on the cooling system of my 560SEL. When I purchased the car, the thermostat was stuck open, the fan clutch was not operating correctly and neither was the Auxiliary fan. I feel much better about driving it on hot summer days with these systems all fixed. I also plan to adjust the cut in point for the Auxiliary fan, which will be covered in a later article. […]

By: M117 fan controller prototype « Classic Jalopy

M117 fan controller prototype « Classic Jalopy — Wed, 07 Apr 2021 23:42:38 +0000

[…] couple of months ago I tried a modification on my 560SEL to trigger the auxiliary cooling fan earlier. The […]

By: Jason P

Jason P — Mon, 15 Mar 2021 11:54:21 +0000

I’ve tried this modification but don’t like it for this reason: It makes the heat come on before the coolant is warm enough.

Instead, I’ve rewired the fan circuit a bit: I moved the trigger from the high side pressure switch to the high speed fan relay, and with the help of another relay have the low speed fan triggered whenever the compressor is engaged. There’s no concern with having the fan run when moving down the road… on my 350SDL if the fan clutch is bad the car will overheat if it’s a hot day out, the ac is on, and you’re blasting down the highway at 130k.

For whatever reason the fan clutches for the OM603 seem to be problematic. They either don’t work, or the spring flies off and the fan is on all the time. It moves a lot of air… and consumes a lot of horsepower in this state!! I removed the clutch fan and installed a BMW thermostat switch in the thermostat housing. This triggers the low and high speed fans appropriately. There’s very little space between the water pump and radiator on the 6 cylinder diesel, so I was only able to mount a small-ish fan on the engine side of the radiator, and have a large fan in front of the radiator and condenser pushing air back in. Being a 91 my car originally had the twin fans, but one motor went bad and spares are hard to come by at reasonable prices.