I am reading thru the post because I just found a leak at my coolant sensor coming from the return hose.
It looks like it is coming from the top of the sensor, does that sound like the O-ring and if so how easy is the fix?
I am also reading that these cars have quick disconnect hoses? with o-rings? is this correct? Last car was an e39 540. Haven't really had to do much to my 2005 545 (yet)
I guess at 110,000 the fun is about to begin..
Wondering what or how these hoses and sensor get replaced.

Thanks

 

Wow your lucky, I'm at 99k and so far I just replaced my water pump, thermostat, the two hose with the and reservoir were replaced prior to that and its quick disconnect hoses, like the coolant temp sensor.

 

Please tell me how these quick disconnects work? I haven't had to take one apart yet. I am sure once I do it will seem simple

Thanks

 

You either have to press or slide a particular area on the connector to make it separate instead of twisting. the easiest reference I can think of is a garden hose since I have them installed and occasionaly have to connect the hose to the water spicket. Some systems (ex. fuel lines) may need a special fitting in order to disconnect which can be found at a local parts store.

Replacing the CTS is straight forward once you get access to it:
1-remove old sensor from block using a socket/wrench
2-install new one making sure you use water resistant RTV on the threads to prevent leaking

Hope this helps.

 

Wait until the coolant is cold, get your replacement sensor (~$20) ready, this should be at the lower hose. There is a small clip to pull back, and you just shove the new one on as soon as you remove the old one. If you are quick you should not lose but a few drops of coolant.

But old acidic coolant is corroding the parts of the cooling system I recommend at least a drain and fill.

 

I suggest replacing the hose it plugs into as well, i didn't and it started leaking at the sensor plug again 3 wks later. To remove the quick disconnects, slide a flat blade screwdriver under the metal clip and pry up. the metal clip should stay locked in the up position and then you can wiggle the hose off. Be advised if they've been on the car a while they may be stuck to the fitting and may require some convincing to move.

 

Thanks everyone.
It took all of about 5 minutes to replace the sensor. Once I had the new one in hand I could see how it connected.
I will have to plan to do the other pices in the near future.

Thanks again

 

+1 here

 

Great info.

 

i have the same problem, coolant leak at the sensor. there is few info or pictures about the process. i can't remove the sensor off the hose seat. i have tried 3 times, not seccesful yet. the biggest headache is no space , too narrow to put my single hand.