How Long Can I Drive With Bad Thermostat?

[JH M3]

Just got the CEL, increased emissions warning, and thermostat fault code. I think the thermostat is stuck open since it's running on the cool side. The dealer here wants almost $2000 to replace the thermostat and water pump (I figured the pump should get replaced as well since I'm at 55,600 miles). I found an independent shop that will do it for $1100 but they can't fit me in until next Monday. Since it's not running hot I think I'm OK driving it for a bit but my question is how much? I've got probably 2-3 trips at about 40 miles each to make this week.

The alternative is I replace the thermostat myself and forego the pump. I don't feel entirely comfortable with my abilities to replace the pump but the thermostat seems relatively straightforward.

[Powashiftin]

Originally Posted by JH M3

Just got the CEL, increased emissions warning, and thermostat fault code. I think the thermostat is stuck open since it's running on the cool side. The dealer here wants almost $2000 to replace the thermostat and water pump (I figured the pump should get replaced as well since I'm at 55,600 miles). I found an independent shop that will do it for $1100 but they can't fit me in until next Monday. Since it's not running hot I think I'm OK driving it for a bit but my question is how much? I've got probably 2-3 trips at about 40 miles each to make this week.

The alternative is I replace the thermostat myself and forego the pump. I don't feel entirely comfortable with my abilities to replace the pump but the thermostat seems relatively straightforward.

Check the DIY section. Parts can be had for a few hundred bucks. Good luck

[Locksmythe]

The answer is indefinitely. But your gas mileage will go down by 30+ % because the O2 sensor calculations will not be able to process correctly and the system will default to max fuel mix to compensate. The fuel costs will exceed repair cost in a few months.

[JH M3]

Thanks. So far I haven't seen a real noticeable drop in fuel economy and the heater still works fine. After doing a little more research I decided to attempt the thermostat and pump change myself. I found a good price on a new pump so all told it's going to cost me about $500 including purchasing a few tools that I need. I'll post an update in the DIY forum when complete.

[Richbot]

Which Tstat code is it? I wouldn't (and didn't, when I was in a similar situation at 90,000 miles) change the pump without reason to believe it's having problems, but it's up to you. Not a hard job at all, just messy, I'd recommend pulling the belly pan off so the coolant you spill hits a drip pan rather than getting trapped in the belly pan where you'll smell it for months and it'll make you paranoid you've messed something up and have a leak

[JH M3]

002B59 is the code. I bought a catch pan in anticipation that it will be a messy job. I found a new genuine pump for about $100 less than the average price I've seen so I figured it would be a good idea to replace it as well. Talking to my dealer some cars go 50k before the pump fails and some go 100k. In other words it's a total crapshoot. Sounds like your car is in the latter category.

[TWiTCHY]

I drove on a bad thermostat and temperature sensor for 10 months before replacing it. Did not experience the lower gas mileage as another user stated, but it did take much longer for the car to warm up to operating temp.

[tdott]

Water Pumps on Ms usually last a long time, he might be talking about all BMWs not just the S65. I haven't heard of many failures yet, but it still might be a good idea, why not.

A friend had his S54 wp last until 280k miles.

I did my tstat and flush at 80k and was debating changing my pump, but my friends convinced me other wise. It's really not hard to get it, and it's not really a 'while you are in there' kinda thing all you are saving is some coolant and a few minutes.

[Richbot]

Originally Posted by JH M3

002B59 is the code. I bought a catch pan in anticipation that it will be a messy job. I found a new genuine pump for about $100 less than the average price I've seen so I figured it would be a good idea to replace it as well. Talking to my dealer some cars go 50k before the pump fails and some go 100k. In other words it's a total crapshoot. Sounds like your car is in the latter category.

Maybe I missed one but I have yet to see anybody report a failed S65 water pump on this forum, that sounds like the M50/M52 engine lore being applied to a totally diffferent engine

2B59 could just be the $75 thermostat sensor. You might not even need to crack the system open to resolve the code.

[Richbot]

Originally Posted by TWiTCHY

I drove on a bad thermostat and temperature sensor for 10 months before replacing it. Did not experience the lower gas mileage as another user stated, but it did take much longer for the car to warm up to operating temp.

This was my experience getting 2B59 code only as well, drove it like that for about 5 months, intermittent 2B59 code when it was cold out, usually during the first few miles of driving after a cold start. I have no proof the thermostat was bad, changed it while I was in there because I noticed slow warmup as well and needed to do a coolant flush anyway, but it may have all just been poor sensor performance, the factory sensor had a lot of oxidation and some deposits on it when I took it out, though I think the sensor had an intermittent connection problem as it would sometimes throw out implausible values, hence the code

[JH M3]

Thanks. Based on all the feedback I've decided to not replace the pump but I'm going to replace the sensor and the thermostat. Looks like an aftermarket sensor is less than $15 so why not.

[Locksmythe]

Originally Posted by TWiTCHY

I drove on a bad thermostat and temperature sensor for 10 months before replacing it. Did not experience the lower gas mileage as another user stated, but it did take much longer for the car to warm up to operating temp.

My temp sensor was also very corroded so I probably needed to replace both (and did). Makes sense that the sensor would have been the critical factor in my O2 calculation woes rather than the thermostat.

[Locksmythe]

Oh, one piece of advice: I followed a DIY that said to remove the wire clips with a plier. That only applies to the clips on hoses, and a screwdriver works better for that anyway. The clips on the electrical connections like the sensor are just squeezed by pushing on the center of the wire toward the connector, which releases the tabs on each side. You have to remove the sensor connector to get to the thermostat anyway, so replacing the sensor only adds a minute or two to your thermostat job.

[JH M3]

Thanks for the advice. Strangely enough after I filled up this morning the Check Engine warning went away. I'm going to clear the codes and see what happens. I'll probably end up replacing the thermostat and sensor anyway since they're more than likely on their last leg even if they are working again now.

[Richbot]

My 2B59's sometimes cleared on their own from the dash, but were stored

[dparm]

Originally Posted by Locksmythe

The answer is indefinitely. But your gas mileage will go down by 30+ % because the O2 sensor calculations will not be able to process correctly and the system will default to max fuel mix to compensate. The fuel costs will exceed repair cost in a few months.

Yeah, but running rich for long periods of time is not healthy for the engine or emissions components. I would get it fixed as soon as you can.

[JH M3]

So 5 days after clearing the code it hasn't come back. Not sure if it's worth the hassle of changing the thermostat right now although of course the parts I ordered arrived right after the fault cleared.

[Locksmythe]

As Richbot said, the code will come and go; it did for me as well. The problem is insidious - it will resurface.

[monterey]

Originally Posted by Locksmythe

The answer is indefinitely. But your gas mileage will go down by 30+ % because the O2 sensor calculations will not be able to process correctly and the system will default to max fuel mix to compensate. The fuel costs will exceed repair cost in a few months.

How much truth is there in this? I had the code come up a few months ago and I disregarded it. After it was cleared, it hasn't come back but my gas mileage has always been terrible.

[Locksmythe]

I drove with the temp sensor/thermostat code randomly coming and going for a long, long time because I didn't see anything that said it was important, and it would not come back when cleared. My gas mileage went down to around 13mpg. I assumed it was because I was doing only city driving on my commutes. After replacing both, and the sparkplugs, the fuel economy went up by almost 50%.

[dparm]

Originally Posted by monterey

How much truth is there in this? I had the code come up a few months ago and I disregarded it. After it was cleared, it hasn't come back but my gas mileage has always been terrible.

There is plenty of truth to it. Fuel maps are very complex so as soon as certain variables are way out of whack, the car goes into a "cautious" mode which results in excess fuel consumption.

[oolas3]

Running overly rich can wash the oil off the cylinder walls and break down oil faster.