N52 Thermostat

G

GrimleyFiendish

Member
 Norwich, Norfolk
I've had a search of the forum but couldn't find anything specific to this after a quick speed read of the results.

For the last couple of months my car has been very slow to warm up, according to the temp gauge that is, which takes ages to move off of the blue bar and then only gets as far as the first or near the second white line. The heater still works OK though, eventually.

My thinking is the thermostat is on it's way out but when I mentioned it to the mechanic when dropping it off for a service he seemed to think it was quite low mileage for thermostat problems. I notice there is also a Coolant Temp sender but to my mind (simple as it is) this would either work or not. As the sender is only £9 compared to £60 odd for the thermostat I wondered if anyone here had any knowledge or experience of these symptoms?
 
Your observations sound like the thermostat is stuck open. I'm surprised you don't have a "check engine" light on as the ECU doesn't like the coolant temperature staying low. My Z4 takes 3 - 5 miles of county road driving to fully warm up to just below 100 C as reported by the ECU to scan tool. The temperature gauge shows 1/2 scale at that reading.

Try blocking some of the radiator air flow with cardboard & tape leaving a small open area for safety. This should bring the temp up while driving and confirm thermo is stuck open.
 
If it were the sending unit, you more than likely would get a CEL, and the slowness of the heating seems to parallel the temp readings, so I really doubt it's the sending unit. So I agree, it does appear to be a thermostat issue. While it is certainly a premature failure, I am not surprised. I've found that devices that rely on bimetal response such as thermostats tend to fail erratically. Sometimes they last forever, other times the same device fails after several months.

In case you didn't know, the N52 has a peculiar bleeding procedure. I attempted to summarize it in the following post:
http://www.z4-forum.com/forum/viewtopic.php?f=3&t=43515&p=619586#p619586
 
Thanks for the responses, it's good to get some confirmation. I'm not back at work until the 8th April now so should find time to fit this little job in :)

Cheers for the link about the bleeding proecedure as well, I had heard about it but that information is very useful.
 
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