Sorry I don't think that I'm wrong and neither is the OP's mechanic. He read the error code as stuck open thermostat.

I read my DME and it told me that the thermostat was stuck open. No check engine light.

The error code that you received was for a " I got an error something like cooling below threshold/thermostat stuck open".

There could be several reasons why you have that code including a stuck thermostat. But that code is not a stuck thermostat code.

http://www.obd-codes.com/p0128

interpretive breakdown lol
 

I wasn't referring to the water pump gasket , I was clearly talking about the thermostat gasket :)

My question/inquiry still stands unanswered though. Replacing a water pump is standard maintenance around 100k miles?
That's somewhat discouraging for a german engineered machine lol

I wouldnt suggest that a waterpump is "part of a routine maintenance" But they do fail and when they do, they usually start by leaking fluid, then maybe a bit of bearing noise. When they do, I change them! and for what ever reason, its usually around 100k
as posters have said, its an easy job, the toughest part is getting the fan and rad shroud out of the way, and the belts off. after that, its drain and replace, the gasket is an O-ring which is how every car should be built! no wondering if its gonna seal until its too late! The water pump isnt an expensive part (BMW speaking!) and its peace of mind knowing its not going to fail for another 100k!
(that said, mine is going to be changed in the next few weeks, when i do my serpentine belts and tensioners! :))
:thumbup:

Going to chime in here.

Can confirm thermostat DOES in fact set off an engine code. ie p0125. It will actually give 2 codes under BMW specific diag.

Thermostat, 28$. Fix takes an hour.

They fail (as mentioned) OPEN. Don't bother trying to fix the unit. it has some wax inside and a circuit as far as I have been told?

Haha yeah, I meant thermostat though, sorry. :)

A lot of people replace the water pump when they do a cooling system overhaul. I did get a waterpump with the intention to replace it along with the hoses but with a few anecdotes on line indicating these are relatively long-lived, plus it being relatively accessible, I held off for now. I've read reports of these OE water pumps reaching beyond 100,000 miles, so at 45,000 now, I'm (hopefully) still a ways off. :)

I dont know why you seem stuck on this. Like i said before, it does give a check engine light on the dash. And Persian confirmed it. Maybe your perticylar BMW doesnt, but i know sure as shit mine did. A replacement tstat fixed it.

Persian never stated that the ses or cel came on with the code. He only stated that it throw off a couple of codes. You need to re-read his posting.

I know that a stuck open thermostat will give a DTC but not a SES or CEL as the OP's mechanic found out and as I have stated in my case.

This was my experience when my old 3.0i had an opened Tstat:
- NO SES on the cluster
- Take very long time to warm up/have little bit of heat.
- Temp needle drop down when driving on the hway vs. local streets
- Mpg went down
- Scanner showed one pending (that's why it's not triggering the SES) code: P0128

@ Slick GT1

Daka 3.0
Persian 3.0
Upallnight 3.0
TMV 3.0 (old X5)

All experience a stuck open thermostat with no SES light. You need to read the owners car model before telling them they are wrong.

It sounds like you had your X in for something else and indy mentioned thermostat or did you have symptoms that tied to cooling system?



Since you are only driving short distances it should not harm the engine and it is possible it does not get to proper operating temperature with good or bad thermostat anyway. Regardless, it is not something that has to be done right away.

I would think if the indy wanted to scam you they would have chosen to repair that costs a lot more and requires many hours of labor.If you are concerned about integrity of shop either unlock the OBC and monitor temperature or ask the shop to do so. Then let the engine idle for 15 minutes to monitor temperature before making a decision to replace the thermostat. If indy is trying to put one over on you it will do no good to ask him how he knows it is a bad thermostat. I would either monitor the coolant temp or get a second opinion and prices from to do the repair.

Code or no code, light or no light you will have your answer.