[Bush Pilot]

I've got an 08 335i with 36k mi. Yes. It has sat a lot in a garage.

The engine takes way too long to warm up especially in the cooler ambient conditions we have now. I suspect that either the thermostat is stuck open or that the signal that controls the thermostat isn't correct. I have a BMW code reader, think the brand is AUTEL and it is not reading any codes associated with the thermostat. That said, the battery registration is off so if the diagnosis software uses time that could be messing up the diagnosis software.

So, is there a way to determine if the thermostat is stuck? I suspect that on cold startup, I should be able to feel warm water coming in to the thermostat via the hose and cold on the exit portion of the thermostat which would indicate a closed thermostat.

Any tips on what to measure at the electrical connector to the thermostat? I plan to check the fuses this evening.

Thanks in advance for any helpful info.

[Supahone]

Does the heater blow warm air as the car is warming up?

[Bush Pilot]

This morning with ambient air temperature of 46F, after about 1 minute, I could feel the air coming out of the vents was slightly warmer than ambient.

[lookalikehuuh]

I hope you are not basing your temperature on the oil temperature gauge on the dash. It's fairly normal for the engine oil temperatures to take a while 10+ minutes to reach operating temps, however your Autel should be able to give you live data where you can read the coolant temperatures.

The coolant should come up to temperature much more quickly and should maintain its temperature in the ~210F range.

That being said, definitely don't beat on the car until the oil temps have reached around 180F+

[Bush Pilot]

Is the temperature gauge on the dash oil temp? My car has the factory oil cooler. Is that why oil temps take so long to come up?

Is there a way to verify that the thermostat is actually closed when the engine is cold and started? Assuming that I can read the coolant temperature, how do I use that data to determine whether the thermostat is stuck open?

One symptom I had with a 318Ti when the thermostat was stuck open, the temperature reading would go way down when coming down a long mountain road where we were mainly coasting. Is there a better way to determine whether my thermostat is stuck open?

[ky0u]

Originally Posted by Bush Pilot

Is the temperature gauge on the dash oil temp? My car has the factory oil cooler. Is that why oil temps take so long to come up?

Yes the temp gauge you have is oil temp, not coolant. It is normal for it to take 10-15+ min to get up to temp.

If the slowness of this gauge was the only reason you were suspicious of a stuck thermostat, then your car is more than likely perfectly fine.

If you want extra peace of mind (can never have too much on this platform), I believe there's a way to view coolant temp through the car's hidden service menu through your OBC.
Certain OBD2 scanners will also be able to read this depending on what you use

[Bush Pilot]

Thank you for the input. I am using the slowness of this gauge as in indicator.

Shouldn't I be able to start the car when cold, remove the radiator cap and look for swirling coolant which would indicate a stuck open thermostat. If the coolant isn't swirling around in the radiator when the system is cold then the thermostat is most likely good.

[TheMidnightNarwhal]

Originally Posted by Bush Pilot

Thank you for the input. I am using the slowness of this gauge as in indicator.

Shouldn't I be able to start the car when cold, remove the radiator cap and look for swirling coolant which would indicate a stuck open thermostat. If the coolant isn't swirling around in the radiator when the system is cold then the thermostat is most likely good.

Just look at your coolant temp data when you are driving. I've never heard this before and you won't be able to see much IMO through the coolant tank.

When my thermostat failed I didn't have codes, although eventually I did, but it started when I noticed out of normal oil warm up times. Then, when I looked at my coolant temps, I could only reach operating temp by idling in a lot but the moment I hop on the highway the temps would just drop and drop.

[Jaronbwall]

If he isn't monitoring with a tuner he won't be able to see the coolant temps anyways.
The N54 takes a long time to warm up; equally as long to cool down.

[Saif2018]

Originally Posted by Bush Pilot

I've got an 08 335i with 36k mi. Yes. It has sat a lot in a garage.

The engine takes way too long to warm up especially in the cooler ambient conditions we have now. I suspect that either the thermostat is stuck open or that the signal that controls the thermostat isn't correct. I have a BMW code reader, think the brand is AUTEL and it is not reading any codes associated with the thermostat. That said, the battery registration is off so if the diagnosis software uses time that could be messing up the diagnosis software.

So, is there a way to determine if the thermostat is stuck? I suspect that on cold startup, I should be able to feel warm water coming in to the thermostat via the hose and cold on the exit portion of the thermostat which would indicate a closed thermostat.

Any tips on what to measure at the electrical connector to the thermostat? I plan to check the fuses this evening.

Thanks in advance for any helpful info.

Get MHD and use INPA or Protool to read all fault codes if you haven't already. Use MHD Datalogging feature to see live coolant data.

If its warming up in around 15 mins it's fine.

[TheMidnightNarwhal]

Originally Posted by Jaronbwall

If he isn't monitoring with a tuner he won't be able to see the coolant temps anyways.
The N54 takes a long time to warm up; equally as long to cool down.

You're right but with his AUTEL scanner I figured it could show coolant temps easily.

If not OP, you can google "secret menu coolant temp BMW E92" and you can show them up on your dash that way.

[Bush Pilot]

Originally Posted by TheMidnightNarwhal

Just look at your coolant temp data when you are driving. I've never heard this before and you won't be able to see much IMO through the coolant tank.

When my thermostat failed I didn't have codes, although eventually I did, but it started when I noticed out of normal oil warm up times. Then, when I looked at my coolant temps, I could only reach operating temp by idling in a lot but the moment I hop on the highway the temps would just drop and drop.

Great info. Thanks. I hope I can return the favor sometime. I'm an electrical engineer so contact me if I can support you.

[Bush Pilot]

Originally Posted by TheMidnightNarwhal

You're right but with his AUTEL scanner I figured it could show coolant temps easily.

If not OP, you can google "secret menu coolant temp BMW E92" and you can show them up on your dash that way.

Good info and thanks. Let me know if I can support your efforts.

Bushpilot

[Bush Pilot]

I used the temperature monitor accessed via the "secret code" and my coolant temperature went to 93-96 C (199-205 F) and stayed there during my 40 minute commute to work. My oil temperature, once stabilized stayed around 215-220 F. I'm assuming that says my cooling system is working correctly.

Thanks for all of the help.

[TheMidnightNarwhal]

Originally Posted by Bush Pilot

I used the temperature monitor accessed via the "secret code" and my coolant temperature went to 93-96 C (199-205 F) and stayed there during my 40 minute commute to work. My oil temperature, once stabilized stayed around 215-220 F. I'm assuming that says my cooling system is working correctly.

Thanks for all of the help.

Nice good to hear! Yeah the moment the ambient temps start to dip it takes longer and longer. Here in Canada in winter you really notice it.

[Saif2018]

Originally Posted by Bush Pilot

I used the temperature monitor accessed via the "secret code" and my coolant temperature went to 93-96 C (199-205 F) and stayed there during my 40 minute commute to work. My oil temperature, once stabilized stayed around 215-220 F. I'm assuming that says my cooling system is working correctly.

Thanks for all of the help.

Those are normal operating temps, yes.

[Tyc0]

Yeah it takes forever to wake up on my 08. I have never left the car idling from a cold start and came back to it at full operating temp. Seems like it takes at least 15 minutes for the needle to move when it's colder out.

[bleicht]

My '08 does take a long time but as everyone has said, the oil temp will lag water temp. However, once I was used to the warm up time as reported by the oil gauge, I did encounter a situation where it WAS slow to warm up. It turns out the (coolant) thermostat needed to be replaced. The code was present for this fault but the SES light hadn't illuminated. Regardless, replacing the thermostat resolved all my issues. Cheers.