auxiliary fan runs constantly - PeachParts Mercedes-Benz Forum

87300Diesel · #1 07-11-2010, 01:59 PM

I recently cleaned the engine on an 1987 300d with water/degreaser, and now the auxiliary fan runs all the time including when cold or ac off. I understand that the fan should run based on coolant temp or ac operation. Is is possible that water damaged either sensor? Where are these sensors located? Thanks

Bio300TDTdriver · #2 07-11-2010, 03:56 PM

The sensor is in front near the upper radiator hose. It is red, blue, green, or gray depending on which one you have. It has three prongs on it. You got it wet and it needs to dry out. A few days and it should be OK. Next time you clean you engine, wrap it up and keep it dry. Unplug the two wire prong and the fan should stop. You may need to unplug the single wire as well.

87300Diesel · #3 07-11-2010, 06:59 PM

I located the sensor and pulled the two wire prong which turned the fan off. Do you know what the sensor is called so I can order a new one? It's been a week since it got wet. Thanks for the help.

Bio300TDTdriver · #4 07-11-2010, 07:27 PM

Quote:

Originally Posted by 87300Diesel

I located the sensor and pulled the two wire prong which turned the fan off. Do you know what the sensor is called so I can order a new one? It's been a week since it got wet. Thanks for the help.

Well if it is the original switch it may not work anyway. It is called an auxiliary temperature switch. The one that comes in the car is a 110/128. Aux fan comes on at the first number, AC shuts down at the second. According to GSXR that is too high and he recommends the 105/120 switch from the 126. I'm super paranoid about my new head and run a 100/110 red switch from a 201 gasser. There is also a green 105/115 switch.

As noted above the connector is probably wet as the switch is sealed. If it is original and is working I still would replace it with one of the lower numbered switches. You want you A/C off and your heat on long before you see 128 on the gauge. Having said that there is much debate as to how much the electric fan helps in a properly functioning cooling system.

Bio300TDTdriver · #5 07-11-2010, 07:30 PM

Quote:

Originally Posted by ah-kay

Remove the connector and measure the resistance between the 2 prongs. If it is shorted and engine is cold then the sensor is faulty. It is a temperature switch switching at 100C ( red color ), the other colors switches at 105C. If it is not shorted than measure the prongs to chassis, they should not conduct. The sensor is water proof and watering it should cause no damage. I suspect water got into the connector and shorted them. Make sure the connector is dry and plug it back in and check again.

Part #:

Red: 006-545-42-24 (100/110)
Green: 006-545-45-24 (105/115)
Grey: 006-545-61-24 (105/120)
Blue: 006-545-64-24 (105/128)

Good luck.

You beat me to the answer. Which switch are you running in your OM603s?

ah-kay · #6 07-11-2010, 07:37 PM

They came with the cars, the gray color one. I ordered a red one ( 100C ) for one of my SDL as it seems to overheat with a #14 head. It turned out to be the radiator cap not holding pressure hence I never installed it.

I also installed a switch to turn the Aux fan on at the engine bay for safety sake. Just a small switch to ground the 2 prongs. It saved my butt at the Death Valley.

Jeremy5848 · #7 07-12-2010, 11:53 AM

Following Sixto's lead, I just put a red-top (100/110) switch in my '87 300D Turbo (W124, OM603), replacing the gray (105/120) switch which itself had replaced the original blue (105/128) switch. Given this car's #14 head, I want to give the cooling system as much help as possible.

Testing the car yesterday in the driveway, I put blankets over the radiator to force overheating. After about ten minutes, I was able to get the temperature from its normal 80C up to 100C. The red switch turned on the aux fan and brought the temperature down to 90C in a few minutes. Turning on the heater brought the temperature down another 5 degrees.

I also have a yellow blinking LED in the instrument cluster that comes on with the aux fan. It warns me that the engine is getting hot before damage is done.

Jeremy

vstech · #8 07-12-2010, 01:46 PM

Quote:

Originally Posted by Jeremy5848

I also have a yellow blinking LED in the instrument cluster that comes on with the aux fan. It warns me that the engine is getting hot before damage is done.

Jeremy

I'm gonna do this too! good idea!

Bio300TDTdriver · #9 07-12-2010, 08:16 PM

Quote:

Originally Posted by Jeremy5848

Following Sixto's lead, I just put a red-top (100/110) switch in my '87 300D Turbo (W124, OM603), replacing the gray (105/120) switch which itself had replaced the original blue (105/128) switch. Given this car's #14 head, I want to give the cooling system as much help as possible.

Testing the car yesterday in the driveway, I put blankets over the radiator to force overheating. After about ten minutes, I was able to get the temperature from its normal 80C up to 100C. The red switch turned on the aux fan and brought the temperature down to 90C in a few minutes. Turning on the heater brought the temperature down another 5 degrees.

I also have a yellow blinking LED in the instrument cluster that comes on with the aux fan. It warns me that the engine is getting hot before damage is done.

Jeremy

I've been running the 100/110 aux temp switch for 5 years. The others are too high for me.

Jeremy5848 · #10 07-13-2010, 07:33 AM

Quote:

Originally Posted by vstech

I'm gonna do this too! good idea!

See this thread for details. The alarm was built while I still had one of the other switches in the water jacket; if the picture of the engine were taken today, the switch would have a red top.

Jeremy