Thermostat reliability
 

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 :)

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....

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 ?

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.

Very common failure item on the M54 engine.

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

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.

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! ;)

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.

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.

+1 to all of the above! so +....12?

I would also suggest a metal impeller water pump but not URO. I avoid URO like the plague.

I do too, normally. Just to clarify for the OP, I wasn't suggesting a Uro water pump. Just the pulley, as it's surprisingly good quality.

I have not seen an M54 water pump with a plastic impeller in years. The pump to have is the Stewart, but it's three times the cost of a Graf. I have one on my 330i; it's warrantied "for life", whatever that's worth.

I replaced the tensioners/pulleys already with INA units. Would the crack in the water pump pulley be visible before removing? Is the aluminum one considered an upgrade ?

Ok, I didn't realize the original water pump pulley was plastic! Yes, already have the water pump with metal impeller ready to go. Good to know that wahler is the OE for the thermostat but too late, already ordered the BMW for almost double the money, crap ;( I didn't want to take a chance on that. The expansion tank on mine looks like it might have been replaced, looks newer and has BMW parts sticker on it. Did BMW have a change up on the expansion tank ?

And yes have had the E30 cap ready to go but haven't put it on yet. up till now I never noticed much pressure in the cooling system. Seems as if you run the level on the low side the pressure never gets close to what the cap is set for. I Imagine might be different when the weather gets hotter though. I do want to still rig something up for the low coolant level sensor as well.

While it's theoretically ingenious idea to vary opening temp through DME, I don't like potential issue behind it when heater fails or leaks and coolant makes its way up through the wiring and cause havoc.
Yes, it's rare and only happens with M62TU thermostat, but M54 thermostat is not that much different when it comes to that feature.
Therefore, I went backward in technology and installed 95 C thermostat found on E31 840ci with M62 non vanos engines.
With a simple radiator hose modification and along with Spal fan (fan clutch delete) my X5 runs around 95-97 C with Spal coming on at 102 C if needed as a back up:
http://www.xoutpost.com/bmw-sav-foru...ch-delete.html

I don't know if I agree with the thermostat change over but the fan clutch delete looks like it might be a good thing. Mine seems to be working fine but does show a bit of leakage. I've heard some horror stories about the cheaper replacements and the BMW one is really expensive. I was leaning towards replacing with the Sachs clutch and maybe a new fan blade.

You need this:

http://www.xoutpost.com/bmw-sav-foru...16k-miles.html

:iagree:

Nice DIY posting by the way.

One more recommendation for the the HEPU Water Pump, I have one running in a 528 installed 5 years ago and it is happy happy happy.

Yes, I ordered the Hepu water pump awhile back (not installed yet) looks good and has "made in Germany" all over it :)

I just had to replace the thermostat for the second time in the last 60,000 miles. I'm thinking the dealer had a bad batch of OEM parts maybe?

Here's my repair and maintenance recap including cooling system service intervals for your reference:

On a regular basis:

> Rotate tires, inspect pads & Rotors, CV boots, general lookover every 5000 miles
> Oil / Filter change every 8000 miles
> Brake fluid flush every 30,000 miles
> Replace belts and clean CCV every 100,000 miles
> Replace differential and transfer case fluid every 100,000 miles
> Replace sparkplugs every 120,000 miles
> Replace expansion tank, coolant and hoses every 150,000 miles
> Replace bake pads every 163,000 miles (Akebono ceramics)
> Replace rotors??? (237,000 miles on current Brembos)

My unplanned repairs have included:

> Front axles at 60,000 miles (Prior owner didn't maintain CV boots)
> FSR at 78,000 miles
> Two sparkplug coils at 124,000 miles
> Alternator at 126,000 miles
> Front driveshaft at 136,000 (used a salvage transfer case for cost savings)
> FSR (again) at 159,000 miles
> Thermostat at 176,000 miles
> Rear differential seal at 200,000 miles
> Secondary air pump at 224,000 miles
> Rear suspension bushings and upper control arms at 242,000 miles
> Thermostat (again) at 245,000 miles - at least it was warranty this time
> Steering column double U-Joint shaft at 245,000 miles
> Valve cover gasket at 245,000 miles
> Both fuel tank sending units, fuel pump and canister at 245,000 miles
> Aux fan when the harness got chewed up in the mechanical fan and shorted out at 259,000 miles
> Pre-cat O2 sensors at 260,400 miles
> Water pump at 262,800 miles
> DISA Valve and MAF at 263,800 miles
> Thermostat (again) at 299,00 miles (don’t know what’s going on with these)

The "Expected" replacements have been:

> All four window regulators
> Driver door handle carrier
> Front axle outer CV boots (each side one time)
> Front tension struts

All in all, except for the front driveshaft job that cost $4200, I have really been happy with the vehicle. It doesn't get babied, but I do monitor and maintain it. I think a lot of my good fortune is due to four things: I live in Texas with short winters so I don't have a lot of the CCV condensation problems, my daily commute is 60 miles so the engine oil always reaches full operating temperature, I run the "M" series viscosity engine oil from May through September when I my driving includes 3000 miles of towing a 1400 pound Waverunner and trailer, and I stick with Shell gasoline.

Additionally, I don't change the transmission fluid! I'm a firm believer in leaving it alone and simply installing a full re-manufactured transmission if it ever becomes necessary.

With that, I'm off towards 500,000 miles!

2002 X5 3.0 300,600 miles
2014 428i 17,400 miles

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

Thanks, that's some really good info! :) A bit scary about the thermostat though especially since I ordered a OE BMW one thinking that I didn't want to be replacing a good factory one with a cheaper aftermarket one that might fail sooner than if I left the old one in. Hopefully that doesn't backfire on me! Really good to hear from someone who has some big miles on :)

Since the clutch fan is the primary fan, when I went to an electric fan I set the electric fan to come on just prior to when the aux fan kicks on. I also wired it so it continues to cool after the ignition has been turned off. The controller I have is adjustable so I can set it anywhere from constant on to not a good idea.