Thermostat reliability

[80stech]

I'm considering replacing the thermostat on my 2004 X5 3.0. It's working fine but I was wondering what are the chances of it failing? Anyone actually had one fail or do they just usually get replaced as a precaution ? Thanks for any input, Cheers

[kevinkay]

replaced mine at 103k miles as precaution while changing water pump as precaution.

IMO, on parts that are "maintenance" rather do it on my time on a sunny day in the driveway then waiting for it to fail on the highway....

[80stech]

I agree with the water pump and will be changing mine as well, that's what made me think about the thermostat. The water pump is known to fail though but I'm wondering what really is the chance of the thermostat failing ?

[upallnight]

Normally they will fail in the open position which means that in the winter time it will take the X a little longer to warm up. You can scan the X and if the thermostat had already failed, it will post a DTC.

Worse case is that it may fail in the close position at which time the engine will overheat and if you don't stop you risk warping the head(s). If the engine does start to overheat, turn the heater to as high as it will go and turn the blower fan at high speed.

[Scott ZHP]

Very common failure item on the M54 engine.

[80stech]

Ok, I'm convinced. Order placed! Thanks for the input

[g300d]

Looks like you are doing cooling system work since you were asking about the fan also?

How old are your hoses? If there is no history of replacing them I'd look into that too.

I held off on replacing the thermostat as PM because it is relatively easy to reach at the front of the motor so I figured just do it if it breaks. As mentioned, they usually break stuck open anyway.

[80stech]

Yes, going to do some/most of the hoses as well. Biggest problem is that I just bought the vehicle in the fall and don't have any service history so it is likely that some of the parts I'm changing have already been changed. I don't might changing a part with high mileage and prone to failure, but replacing a part that has already been replaced and probably would have lasted the rest of the useable life of the vehicle bugs me. I guess I just have to suck it up!

[mferek]

Yeah, might as well replace it while you're in there if it's old. Make sure you check the water pump pulley. Mine had a big crack in it and was probably ready to fly apart. Pretty sure it was original and I was at about 160k miles when I did the cooling refresh.

[Scott ZHP]

URO aluminum water pump pulley, $20. It's worth it.
Check your tensioners and idler while you're at it.

IMO, the cooling system on an M54 needs attention/maintenance in this order:
- expansion tank, replace it with Genuine BMW or Behr; use an E30 rad cap
- water pump, several brands, none of them have plastic impellers anymore.
- thermostat, Wahler is the OEM
- belts/hoses; Contitech or Rein; brass screw for upper hose bleeding
- tensioners/idler; INA
- rad, if more than about 150k miles; Behr or Nissens

Most guys address all of these in one shot, except maybe the radiator. If you are replacing the expansion tank, you will also want to order a trans thermostat; they rarely come out in one piece. Sometimes they don't want to come out at all, lol.