Thermostat

[Daka]

I'm thinking I'll let it go for a while and see what happens, she's never more than 10 minutes from the house....and I'll make sure she keeps an eye on the temp gauge.
Probably with the next service I'll have the coolant changed...(it's now only at 68,000 miles, not a lot for an 06)

[g300d]

Doing a bit of research, as mentioned by others the thermostat mostly fails by keeping the engine TOO cool.

Do you have the high instrument cluster and unlocked the OBC? I would monitor the engine temps via test 7 (or 9, I cant recall exactly which ATM).

As per various BMW forums the M54 runs at around mid to high 90's. Failed 'stats cause temps to be consistently at the low to high 80's from what people have reported.

Sometimes the classic symptoms of failed thermostats like long warmup or temp needle below middle dont show.

A lot of people do report poor gas mileage as a common symptom though. Not that it'll sip fuel like a Prius, but there is reportedly a noticeable diff.

[Acidphase]

If he's in Florida and it's stuck open I doubt it would ever take that long to heat up.. The car will normally always run fine with a faulty thermostat UNLESS it's stuck closed that's more of a problem because of overheating.

In general though normally thermostats are very easy to replace , on some cars you just have to make sure to get all of the old gasket off to have a nice smooth surface for the new one. If not leaks will develop.
I'm pretty sure I located mine just by a glance without even looking it up online , if it is where I think it is it's not that hard to get to. (whenever I get a new car I look for these sort of things it's a common thing to go)

Someone mentioned:
New Water pump after 100k? This is normal routine maintenance????

[TiAgX5]

BMW waterpumps don't use a surface gasket that needs to be scraped off, they seal with an o-ring seated in a groove, that "tight slip fits" into the engine block waterpump bore.

[g300d]

Yup OP the waterpump on these motors is easy to get to.

Pretty much at the top front of the block.

[Daka]

Ah ha, I have noticed that when I fill it (as I said I don't drive it much, but I don't like my SO going to gas stations, so I fill it) I have noticed that it has gone from about 16 mpg (80% local driving) to about 14....maybe I should just change the t-stat anyway if it is that easy!

[z168]

Yes a dead thermostat throws a code but you need diagnostics for it. It wont throw a dash light

[TiAgX5]

Yeah, when the t'stat allows the engine to run cool MPG drops about 20%.

[upallnight]

Originally Posted by SlickGT1

On our 4.8is, the tstat has a sensor. That sensor technically measures when the tstat fails. I know this because I had it happen. It was a ridiculously simple job on the 4.8.

That being said. Does your car take a really long time to warm up in the morning. That is also an indication of a failed Tstat.

I also question how these mechanics know you have a failed tstat. If there is no code for it, how did they come to this conclusion?

This what the OP stated

The shop is saying that my thermostat need replacing, this from their computer, no indication on the dash

A failed thermostat will not set off a check engine or service engine soon light, but it will be logged into the DME as a problem, which can be retrieved if you have the proper software connected to the car.

[SlickGT1]

Originally Posted by upallnight

This what the OP stated

The shop is saying that my thermostat need replacing, this from their computer, no indication on the dash

A failed thermostat will not set off a check engine or service engine soon light, but it will be logged into the DME as a problem, which can be retrieved if you have the proper software connected to the car.

Nope you are wrong. My check engine light got set off. Thermostat is directly related to emissions. Car can't warm up fast enough, means it is running rich, and will throw a check engine. I got an error something like cooling below threshold/thermostat stuck open, with a basic OBD2 scanner. Something more advanced with INPA, but check engine definitely lit up for this error.