Thermostat not reaching normal temp (midway on the dial)

W

wolfgangCoupe

Member
Hi Guys,

Calling on all zed-heads for some advice on a new issue I'm having.

As you can see from the picture, the thermostat is only showing upto a quarter way on the dial. It floats very slowly in this range, but never upto operating temp or back into the blue, even after a long run of upto 3 hours.

From some research and chat with a mechanic friend, the first port of call was possible a sticking thermostat? However there is also suggestion on the forum it could be a water pump on the way out, which is obviously significant more expensive.

Hoping for the best here but any advice would be appreciated. I'm a keen fixer so any work will be done by myself.

EXTRA DETAILS:
- I've replaced the oil filter housing and oil cooler gaskets, replacing both the oil and the coolant. Having driven around europe and doing about 4000 miles since then I highly doubt it's anything to do with this work.
- The car has had a water pump and thermostat only 40,000ish miles ago
- MODEL - 2006 Z4 E86 3.0si Manual

Let me know of any theories and I'll answer any further questions!!

WolfgangIMG_0305.JPG
 
That is typically where all of my Z4s normally sat although they did get nearer to half on hot days in traffic.

The only exception was my first 3.0Si that got into the red when the water pump died!
 
Get a decent code reader on it, the. You can check (a) the actual water temperature; and (b) any error codes indicating a problem with the thermostat.

But it looks fairly normal to me.
 
As said, get a code reader. It will check to see if there is a problem with the pump, unlikely, and also give you the engine's running temperature. An open thermostat will provide you with poor heat from the heater and you may also see mayonnaise on the oil filler cap.
 
I’d expect it to sit half way on the gauge. Admittedly my car has a different engine but that’s where mine is- and on every other car I've owned as well!
 
------ UPDATE ------

After reading all the feedback and doing all the research I could, I pulled the trigger and bought a thermostat from EuroCarParts and fitted it!

Luckily the thermostat is super accessible from underneath the car, so all the job entails is lift the car onto jacks stands, take the front undertray off and drain the coolant. Once this is done I undid all the pipes from the thermostat ( :headbang: easier said than done!!!). 2 hoses are jubilee clips which were easy, but the other two were guided clipped coolant hoses which were bloody stubborn. Only tip would be to try and leverage then off with a flathead screwdriver whilst being carefull not to break the hose.

Re-adding coolant is bloody hard work but all seems well and back up to normal temp! All for £60.

IMG_0330.JPG

Screenshot 2024-10-04 at 19.19.32.png
 
hello
If you go into the hidden menu of the instrument panel you can see the temperature, the thermostat in these cars opens at 103 degrees Celsius.
 
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