Coolant Temp sensor broken on 300E???
 

Hello Board'

My aux fan kicks in when I turn on my A/C, but if I have the A/C off and have my car idle for a few minutes, the temp will hit 120 C !!! I noticed that the aux fan does not engage. When I unplug the 2 prongs on the coolant temp sensor and touch them together, the fan will go on at full blast. Could the coolant temp sensor be at fault???

sounds like you found the problem and answered your own question. SENSOR!!

Mike, I know this question has been covered somewhere on this board but I noticed on your signature that you have debadged your 300E. Did you use the dental floss and 3M adhesive remover for this operation? Reason I'm asking is because I've been wanting to do it to both of my cars but can't remember what type of adhesive remover was mentioned, 3M is the only thing that comes to mind.

The ACC sensor is separate from the temp gauge sensor. The temp gauge sensor is on the head between the #4 and #5 cylinders. It's a single post sensor. Pull off the wire and the gauge pointer will go limp. [On a W126] the ACC (105C/115C) sensor has a 2-pin connector and a single pin connector. The 2-pin connector has a constant ground wire and a wire to the Klima relay. The single wire goes to the electric aux fan circuit. When you hit 105C, the electric aux fans kick in full tilt. When you hit 115C, the compressor cuts off.

A bad 105C/115C switch is not uncommon but I think you have deeper problems if your car overheats in a few minutes while idling with the AC off. I can idle my 300SE a long long time with the AC off and the electric fans won't kick in.

Sixto
95 S420
91 300SE
87 300SDL
83 300SD

JetForeman, Well my car is de-badged because it has a new paintjob and the body shop took off the emblems. I have debadged cars using dental floss and WD-40 and wiping the residue off. It removes even the toughest emblem adhesives.


sixto- well, when I say a few minutes, it actually is about 15 minutes. The temp will hit about 115, but will not get above that. I guess my coolant temp sensor is at fault.

Check you thermostat and the coolant cap!
 

They are cheap and cause a lot of temperature related problems!

Found the culprit!
 

Hello Board,

The problem turned out to be the temp sensor that controls the aux fan. It was a $15 part that could have cost me another engine.

Thanks for all the help guys!