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-

RB, yeah that would be nice to know, please do!

My original, and three subsequent replacements done by the dealer, have all been Behr. I would agree with the "soft failure" comment as the last two replacements were based off of stored codes and not a visible temperature gauge indication.

2002 X5 3.0 312,300 miles
2014 428i 22,800 miles

2004 325i sold at 123,600 miles
2001 325i sold at 66,000 miles

1970 Firebird - Under restoration

^OK good to know - mine was replaced but I don't think the dealer so probably a Wahler, its been fine, but if I do the water pump preventatively when I do the rad hoses and Exp tank due to age, I'll get a new Tstat in there as well -

Fan clutch is new.

I was thinking that might be it so I checked how the fan is running when the temp goes up and when it goes down.

Air flow was the same, difference was when the temp is going down the air being pulled by the fan is hot.

Which leads me to theorize its a thermostat problem.

Well as promised I got my idler and tensioner pulleys replaced with new INA units and new Continental belts - with 30k miles but 5 years on the ones I replaced previously both pulley bearings were making noise when spun which was my cold squeal at startup - all quiet now

I did get to peek at my OE (BMW stamped) Thermostat and it is in fact made by Wahler - would be interesting to see if a currently produced BMW thermostat is a Wahler or Behr unit, perhaps mine is older and the newer dealer units have been superseded by Behr.

So I guess mine is not a thermostat issue. Replaced it with a new Mahle-Behr one and I still dont have my old 92-93c average temps.

'Stat was a BMW-marked Wahler. No infamous leak on the heating element.

Maybe there is some air left in the cooling system?

Just another guess: do you have automatic transmission? If yes, there is another thermostat #4 on this pic: RealOEM.com - Online BMW Parts Catalog
Don't know if this one might cause your temperature issues...

Yes that thermostat should be changed especially if the vehicle is over 100K miles. Good piece of mind maintenance

Gawd these cooling systems are complicated. Ive been spending a couple of days reding up on them.

That thermostat only affects flow to the transmision oil cooler.

When engine is cold:
- The engine thermostat shuts cold water flow into the engine so it can warm up faster.

- The trans thermostat allows water from the top radiator hose through the expansion tank and to the trans oil cooler, so the gradually warming water heats the atf along with it.

When the engine is warm:
-Engine thermostat opens to allow cooled water from radiator into the engine.

- The trans thermostat shuts flow of water from the expansion tank to the oil cooler and simultaneously opens another coolant path from the radiator, so now it cools the trans fluid.

But yeah, anything slightly out of wack could explain slightly elevated but not overheating temps I guess.

Yes you are right, though it's a not the a "main" part of the cooling system it may probably cause your temperature trouble... Had a similar issue on my 530d (M57): the thermostat of the EGR was the cause in that case.

Interesting, thanks for sharing your experience!

I took a gander at the analog values in INPA and I noticed the rad outlet temps are really low, around 65-70c, even with Ktemps at 96-97c.

Then when Ktemps start to go down, rad outlet temps go up to about 80 or so.

It does seem to point to the thermostat, but it's new.

WTH!