Does this sound like a thermostat issue? - update, nope.
 

As I posted in a few other threads, I'm chasing a higher than normal Ktemp situation (but not overheating or even enought to move the analog gauge) on the 3.0.

Normal observed is 92-93, brief bursts to 96-97, sometimes I go mid 80's on steady highway cruise.

Lately it's 96-99, that goes down to 86-87, then back to 96-99.

I stood infront of the car with the hood up and observed this:

From 96-99, temps would start to go down and the engine fan is obviously pulling air through the rad. If you put your hand behind the fan the air flow is steady and hot.

While this is happening, the airflow is steady, but gets less hot. Ktemps reflect this.

At mid 80's the airflow is still steady. After a while Ktemps start to go up.

But...even as it gets to 90 and above,the airflow is not hot. It can get all the way to 99 and the airflow is still lukewarm. Sometimes you can even feel the fan decouple and the Ktemp is still 96-99.

Then all of a sudden, the air behind the fan gets hot, and then you can see Ktemps go down.

I think the Ktemp goes up because the thermostat keeps coolant from the radiator. The up and down is the thermostat cycling differently from before.

That's my theory now. But I've never come across any other BMW owners that have experienced the same. Mostly people having 'stats stuck open giving lower than normal temps.

What do you guys think?

Update: replaced 'stat, still dont have my old 92-93 deg ave temps. Now moving on to coolant system pressure testing to look for leaks and other possible problems.

You can remove the old thermostat, place it in a pot of water with a thermometer and bring the water to a boil to see at what temp the thermostat is fully opened. But if it was me, if I'm going through all the work of removing the thermostat I would just replace the thermostat with a new Whaler thermostat. My dad on the other hand will just test it before replacing it since he doesn't like to buy new parts, but his time is free.

Yeah, with the low cost of the part, I'd replace it while I'm there too!

I've read the Behr vs Wahler debates and was leaning towards Behr though. The Wahler design IIRC puts the wax and electronic heater element outside the housing thus needing a seal between wax element and main housing, and they sometimes leak at that seal. The Behr design puts everything inside the housing. Any particular reason for leaning towards Wahler?

^^Good question - I know theres only a $5 difference between the two - has anyone had their OE thermostat off recently and checked what brand is stamped on it? I would just buy the equivalent of it just not the "Genuine BMW" version - FCP sells the Mahle/Behr and the Wahler, both made in Germany, which the OE version also says German made.

Well when was the last time the thermostat was changed. In any event its a good maintenance procedure to just go ahead and change it out and move on.

Jay, the thermostat is the original as far as I know. It was on since I got the truck a few years ago at around 26k miles.

RB, yeah, there is a lot of discusion on that in the other forums. No clear preference I can see. Wahlers can leak at the seal, and Behrs can have soft fail issues. Threads going back to years on these lol!

How many miles do you have on the vehicle now?

Jay, sorry forgot to put that, I'm at about 65k now.

Bcredliner posted an interesting observation in his electric fan conversion thread.

He said you cant control engine operating temp via fan, the thermostat does that.

True the fan can only control operating temp if the water flow is open all the time.

It makes sense indeed and it seems to be whats happening in my case.

Cant think of anything else it could be at the moment.

Well when I'm doing my belts and pulleys this weekend I'll see if I can find out what the OE thermostat is - or at least the one on my car now as its been replaced once, years ago by the previous owner-