[ridemore]

I am still working on getting the coolant fan to come on when car (’85 190E) is hot enough. I discovered that the old two pin sensor won’t activate regardless of engine temp on the dash. I can unplug the connector off the pin, jump both wires at the connector with say a paper clip, and the fan magnet will activate right away and fan will run (on water pump speed). Plug the connector on the sensor and no connection.

So I bought a new BEHR sensor for $40 and the first time I installed it, fan activated around the 80 mark on the dash. But after it cut off (3 or 4 minutes later), it never came back on when temp went even next to the 120 mark. Unplug and jump sensor wire at the connector and magnet will activate promptly. So there is always 12V available at the sensor connector. The sensor is just not being consistent in letting power get to the fan magnet.

I went to the salvage yard and got a couple used 2 pin sensors off the 300E & 190E (same for both). I installed one of the old ones yesterday and fan came on slightly after the 80 mark on the dash. However, after it cut off minutes later, it also won’t activate any more, even as temp got up close to 120 on the dash. While it is close to 120 and engine idling, I unplugged connector at the sensor, jump the wires and get fan to activate and bring temp down to around the 80 mark. I can only test one sensor per day as I have to let car cool before swapping out the sensor for another used unit the next day. So, when I get home from work this evening, I will swap the sensor out and try another. I also installed a new made in Germany thermostat.

What am I doing wrong? Does anyone know where the dash temp should be for fan to activate? Am I overlooking any component? Jump the two wires at the 2 pin coolant sensor and you will activate the fan every time. How can these sensors be tested off the car? I picked up 2 extra used units to try.

Greg

 

[284037]

Was the sensor seated properly?

 

[ridemore]

Yes, the sensor is seated correctly. The original sensor I removed from the car seems to be a half inch longer than any 2 pin connector available for sale today. I am refering to the probe that sticks out at the bottom and is submerged in the coolant. The old one looks to be original (23 yrs old) because the former owner just bypassed the sensor and ran a jumper wire to a switch inside the car. This connection has been removed and i am trying to get the car to operate as engineered (off a working coolant sensor).

 

[284037]

Maybe you don't have enough coolant or you have a bubble right below the sensor. Try purging the system or when you remove the sensor pour some coolant down that hole then put it back in.

 

[ridemore]

You may have a valid point there about coolant not getting to the sensor. I was also in the process of flushing the system due to rusty coolant from the car being in storage for years. My process has been to firstly drain block and radiator completely (while engine is cold), replace any sensors as needed, then crank car and let temp build up gradually. Even though coolant filler tank seemed full, as soon as car is cranked and water pump gets involved, water level in the tank usually drops and triggers the low coolant warning light on the dash. It usually takes about 1.5 gallons (in all) to fill it back up to where water level is holding steady and I can put the cap back on the recovery tank. I did not bleed any air out of the system during refill. I seem to have read somewhere that any trapped air will eventually work its way out to the recovery tank.

By purge, you mean to open the little nut on top of thermostat housing and let air escape as water is added, right? I will do that today and see if it helps. Maybe water level drops after thermostat opens and sensor probe is just not immersed in enough coolant anymore?

Greg

 

[284037]

^^
It's a theory but you will find out and let us know

 

[macdrone]

air bubble

If you have an air bubble issue take off the radiator cap top off the tank and run it. All air bubble should work themselves to the tank and be gtg. After its up to temp and topped off you should be able to put cap on. Make sure you do a really good flush if there is rust or issues will most likely come back quick. If you have rust in there someone used a corrosive coolant most likely according to the owners manual which is hard too fix.

Good luck.

 

[1987190E2.6]

Could my car be running rough because an Air Bubble might be in my Cooling System? I just flushed my system out, it's possible an Air Bubble is in there.

 

[BenzDuino]

Hi there, are you sure the sensor you bought is a thermo contact sensor, don't forget there are two types of sensors those who send values to the ECU and dashboard, and there are those acting like a relay letting the current pass through at a certain temperature. In the case of the fan 100°.

 

[Stretch]

It is nice to be helpful but the post before yours was seven years ago.

 

[zephyrueffer]

Lol^
On another note, different colored switches have different resistances. Putting the wrong colored switch could cause the fan to not engage.