E39 528i radiator coolant sensor

[ethanpepp]

I am trying to find a DIY to replace the radiator coolant sensor. I see it is also listed as fan switch on some sites. It is the 3 wire sensor that goes directly into the left side of the radiator near the reservoir near the top. Not sure how much fluid will come out and steps to bleed after that. Anybody have a write up or just know the steps?

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[StephenVA]

That sensor is tapped into the side tank of the Radiator. All the anti freeze will flow out above that point. There is no DIY as it is just a deep socket with a 3/8 " drive ratchet and an extension.
Recommendations: Drain the Rad 1/2 way down, remove the wire connector, unscrew old part, and install the new one, then reconnect the connector. Refill with 50/50 antifreeze and bleed as necessary.

This one is approx 20 mins work.

After completion, take a few mins and clean up under the hood with Dawn Dish detergent, a brush, a sponge and flush with clean water. Air dry with compressed air and or towels. Start engine and let it warm up. Working on a clean engine makes your life easier as you can see what is leaking.

[riverdadd]

Bleed procedure is well covered in the FAQ / DYI section in the top of the forum page.... Very helpful stuff there, for me when I joined the e39 community. Welcome to the forum.

Cooling System Bleeding

[JimLev]

Welcome to the forum Ethan. It is the fan switch. Do you think it's bad because the aux fan isn't working?
If so it could be the resistors that are mounted to the aux fan frame.
If I was doing this I'd put some sealant on the threads of the new sensor, unscrew the old one, then quickly screw in the new one.
You might lose less than a cup of coolant if your quick, no need to bleed, just add a little coolant.
Then you can follow StephenVA cleanup procedure.

[ethanpepp]

Thanks everybody. I figured it was pretty simple, but this car is temperamental and wanted to make sure. I even got lucky enough to have the infamous door handle snap off snafu. The temp gauge goes down to around the quarter mark under heavier load, and back to normal at idle. I know it is most likely the thermostat or the electrical wiring to the thermostat but I am replacing all the parts I can since the system overhaul was done 8 thousand miles ago with new water pump, radiator, thermostat, hoses, belts, pulleys. Next will be the thermostat most likely but it is a pain in the ass.

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[edjack]

I am trying to find a DIY to replace the radiator coolant sensor. I see it is also listed as fan switch on some sites. It is the 3 wire sensor that goes directly into the left side of the radiator near the reservoir near the top. Not sure how much fluid will come out and steps to bleed after that. Anybody have a write up or just know the steps?

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That appears to be the RIGHT side of the rad.

[mattmar1]

thermostat's not a big deal to do.