In the last few days, I've noticed that while idling at a stoplight or in park, I hear what sounds like a fan or compressor coming on at a pretty frequent rate. The water temperature needle will be a little above the normal resting degree point (can't recall right now exactly what that number is), the fan/compressor will kick-on for about 10-15 seconds, then shut-off. The temperature will lower closer to the normal resting point, and all will be well for a few minutes, then the sequence will start again.

I checked the coolant yesterday, and it was below the minimum mark. So I filled it up this morning thinking that would solve the problem. After driving to work (about a 1 hr. drive), the fan sequence was back when I parked at my office.

FYI, it doesn't seem to happen unless the engine is warmed up, and it's just started since the weather here in Texas has gotten a little cooler (between 40 & 70 degrees throughout the day).

Any ideas?

 

how much coolant did you have to add? Did you have the AC running? Running the AC turns the fan on, but shouldn't make temps rise to much.

 

It was the first signs of the temp sensor going I guess cuz soon the fan ran longer and longer / more frequently until one day I parked, came back an hour later and the fan was still running. I pulled the battery cable to keep the fan from draining everything and made arrangements to take the car in the next day. In the morning I connected the fan - and you guessed it - the fan came right back on.

Eventually the entire fan assemply was replaced under warranty. I thought they could just replace the temp sensor but they pulled the entire assembly - a much larger project. I hope I never have the same problem after I'm out of warranty... or maybe someone with a Bently book can tell me how just the sensor could be replaced...

 

The A/C hasn't been running when I've noticed this happening. And I'm not sure exactly how much coolant I added, though I would say that the level was about a half inch below the minimum mark on the reservoir, and I filled it up to the maximum mark.

 

Hmmm, very interesting...I'll definitely keep an eye on any increase of frequency or duration. It does sound like I may have the same problem though...

 

Yeah, adding half inch worth of coolant is not enough for you to require bleeding the system. Okeefe's experience hopefully helps you diagnose the issue though, sounds likely.
good luck man.