Puzzled about engine temp reading: NOW SOLVED

[Stefano85]

Hi! You might remember me from the last 3 Ace cafe meetings (or maybe not xD)
Silver 3.0 Z4 red interiors
Recently it started to do something new. Before the temp guage was going to the middle and staying there no matter what. Now I was getting the symptoms of a stuck open thermostat (the gauge was barely making it to the middle, and was dropping one notch while driving).
Using the "secret" menu 7.0 I noticed that the coolant temp never exceeded 72-76 C (stupid me I never checked the reads when the temp gauge was behaving normal)
Now the odd part. I'm sitting in the car idling from 40 min and engine is at 76-77. When it gets there the fan starts spinning until the temp goes back to 75-74
Shouldn't the fan start spinning at 90 or above?
I still think something is off since the temp gauge fluctuates but maybe is a sensor or the gauge?

 

[Scooba_Steve]

Using the "secret" menu 7.0 I noticed that the collant temp

Does it also show oil temp?

If both coolant and oil are the same then sensors are most likely fine.

If you can't check then I'd just suggest swapping out the thermostat as the cheapest first test, though when I did this on my F10 the first one I bought didn't cure the issue (it was faulty).

 

[Stefano85]

Mmm good point! I can't see an option for the oil temp in the hidden cluster menu https://z4-forum.com/forum/viewtopic.php?t=15176
But I have a cheap obd scanner that I can use with my phone
It was reading the same engine temp as the hidden cluster menu and hopefully il will show the oil temp as well

 

[Stefano85]

Sooo, I finally went to to the mechanic and changed the thermostat.
230£ later (!) it seems tha the issue is solved!
Now the car warms up to 90°C in about 20 Min when idling (not driving), then reaches 100-103°C, and at that point the the fan kicks is, bringing it back to 99-100.

The only thing I was a bit disappointed about is that although they refill 3 Lt of coolant, this morning I noticed that it was way below the minimum (I could not check yesterday at the mechanic since the car was warm)
I put 0.4-0.5 Lt of tap water to bring the level between min and max (cold engine) and then ran the test above. I hope is fine...

 

[Scooba_Steve]

Sooo, I finally went to to the mechanic and changed the thermostat.
230£ later (!) it seems tha the issue is solved!
Now the car warms up to 90°C in about 20 Min when idling (not driving), then reaches 100-103°C, and at that point the the fan kicks is, bringing it back to 99-100.

The only thing I was a bit disappointed about is that although they refill 3 Lt of coolant, this morning I noticed that it was way below the minimum (I could not check yesterday at the mechanic since the car was warm)
I put 0.4-0.5 Lt of tap water to bring the level between min and max (cold engine) and then ran the test above. I hope is fine...

No ideal but shouldn't take it out of the lower end of the ratio. This is one reason I DIY, if you have a set of ramps coolant is easy enough to change, though a vacuum filler makes the job a lot easier.

 

[Zedebee]

Keep an eye out for pools of fluid under your car (front left), the increased temp/pressure may have caused your expansion tank to crack.

 

[Stefano85]

Thx! I'll keep an eye on it... So far I could not see any leak. Today it did something new though, the radiator fan was blowing at full speed for 10 min towards the end of my commute.
It never did it in 5 years... Temp was steady around 100
Will check coolant level again once is cold.
Interestingly, it did not do it the day I brought it back from the mechanic, when the car was already hot when I picked it up, nor during my little test above
Could it be a residual air bubble that moved?

I don't trust mechanics, but I don't trust my skills either xD I know enough to get concerned but not enough to fix it myself

 

[Stefano85]

I think I fixed it! Yesterday I learned how to bleed it and I did that. All clues were pointing towards air in the system (like fan at max speed, top hose hot, bottom cold)
During the bleeding, with the bleed screw closed, I saw coolant raising in the expansion tank. Opening the bleed screw was bringing it down. It did it 2-3 times then it settled. At the end of yesterday both hoses were warm.
I let it cool over night, topped a bit of coolant that I lost yesterday and went for a spirited drive.
All was perfect! When I was giving her beans the temp was dropping immediately around 90 to then go back to 100. No more crazy fan spinning at the traffic light. I think I fixed it.
Tomorrow I'll check the coolant again, if it is ok, I'm going to charge one hour labour to the mechanic xD