Check your thermostat/engine temp - Report In

I am 80% sure I am suffering from a soft t-stat failure. Driving to Castro Valley later today so we'll see what it says. Outside air temp (OAT) is expected to be in the mid 50s. T-stat only has ~55k on it.

I was looking for my post cause I know I went for a drive to see mine. Then I saw the start date.

I still have the printout with all the information you can get in the car and I appreciate that you taught me they existed.

I haven't checked since a bunch of work has been finished.

I am now 100% sure my thermostat is failing. Once reaching 'operating temp' according to my gauge, OBC tells me the temp fluctuates between 74-88 on the freeway and 88-91 when idling or driving at low speeds. That explains why my average mileage is 18.5 mpg a tank.

Will be interesting to see how badly fuel economy is impacted. I think it is quite a bit more than most of use would think?

I know on the M cars, the rear bumper, trunk face and license plate will get covered with soot from the overly rich exhaust. But the M cars are already very cold to begin with, just a few degrees off their operation point, they go down hill fast and start to suffer.

Was just doing temp test the other day...on a long highway run I'm around 90-92. (In 45 degree outside temp) I know in mixed driving, I'm the same as OP...around 89-95. I've seen up to 97/98.

But, what I thought was odd and hadn't noticed it before...this same trip I looked and saw I was at 80 degrees and started to freak (not too bad)...then I realized I'd been in third on the highway for 15 mins! I love third on the highway and often forget to shift! What can I say!

I know I gained 1.5 mpg replacing my stuck open therm a couple of years back...it was the only repair I did at the time. A little later I got another 1.5 mpgs replacing my fuel filter. Easy!

DMAX, even if you were in 3rd on the highway, your temps should have still been a bit higher, HOWEVER, the thing that makes if hard for all of us to follow is if and when the DME has the thermostat heater activated??

I am guessing maybe INPA may be able to monitor this, BUT I am now trying to figure out of and when you can tell EARLY on if the stat is starting to soft fail?

Can you condemn the stat when the idle temps drop as low as 88C?? 86C?

Maybe more data points will help us determine when it is time to toss a new stat in the car. The unfortunate parts is these stats are not cheap and there are not many options that will give economic relief. Did find a suitable Stant stat for the M5 with the inner seal for under $20, when the inner seal from the dealer at discount is over $40 and the stat was about $50 as I recall?

The one thing I can say is you only seem to find the states have failed during the colder months and many times you end up freezing you backside off trying to swap a stat in the middle of Jan.

Ask me know I know!

My car is currently fully warned up and the coolant temp is siting between 93-95°C and its about 60°F out. My thermostat was replaced probably 20K mi ago.

Sent from portable pocket wizard using Bimmer Spell

I noticed maybe a slight increase in MPG when I replaced my thermostat but not much. I replaced my thermostat and then spark plugs 300 miles later and I get just over 30 mpg at 70 mph in an empty car.

Originally Posted by jfoj

DMAX, even if you were in 3rd on the highway, your temps should have still been a bit higher, HOWEVER, the thing that makes if hard for all of us to follow is if and when the DME has the thermostat heater activated??

I am guessing maybe INPA may be able to monitor this, BUT I am now trying to figure out of and when you can tell EARLY on if the stat is starting to soft fail?

Can you condemn the stat when the idle temps drop as low as 88C?? 86C?

Maybe more data points will help us determine when it is time to toss a new stat in the car. The unfortunate parts is these stats are not cheap and there are not many options that will give economic relief. Did find a suitable Stant stat for the M5 with the inner seal for under $20, when the inner seal from the dealer at discount is over $40 and the stat was about $50 as I recall?

The one thing I can say is you only seem to find the states have failed during the colder months and many times you end up freezing you backside off trying to swap a stat in the middle of Jan.

Ask me know I know!

Shanneba has posted before with details of DME specs. for controlling the stat, I know.

I think it hits dead center just below 80, though.

As far as my 80 degree temp when I was in third...I'm not concerned at all...after I shifted to fourth, the temp climbed right up.

The car thought I was racing, I think, and had stat fully open, and in watching the temp for many years, I know that in any ambient temp, when you are press the throttle hard (or maybe go over a certain rpm), the stat will open.

Colder temps and speed also combine to make the radiator pull off a lot of heat...it's impressive what it does!

Don't condemn your stat because you're at 86 degrees...not if you also sometimes hold steady at 92-95...at least that's what I'd guess.

Look for Shanneba in some thread with 'thermostat' or 'cooling' in the title.

HTH

Replacing a stuck thermostat will certainly boost your mileage. I have a very short commute in town and have averaged around 18MPG and after the refresh I took it for a quick errand and it jumped to 25.8 but settled at 20 the next day. It was the horrible starting and stalling at slow speeds that drove me crazy but I've fallen in love with driving once again.

DMAX, forgot to shift out of 3rd, must have been a late night stand up??

Yea, the issue with the electrically controlled stat you have be careful not prematurely condemn the stat because the DME may be artificially lowering the coolant temp at times without you being aware.

So at this point, I think city traffic and idle may be the way to monitor the temps?? But would having the AC on impact the stat heater? Well in the Winter I do not think many will have the AC on unless in defrost mode maybe? How does ambient outside temps influence the heated stat??

Again, I think the only way to really get a handle on the stat behavior is during the colder months, not a fun time to find out you need a stat, but may be the only way to really confirm it is not working correctly.

What I find is most stat seem to open too early, so maybe graphing the warm up cycle you would probably see the stat opening if you know what signature to look for?

jfoj: regarding the t-stat in the bottom of the expansion tank, I replaced that when I did my wife's cooling system overhaul, so that is relatively new as well.


OK so I did the test leaving work yesterday. It was about 40-something degrees out or so, when the car started up, the temp read 23C. I find this pretty odd considering that translates to 73.4F? Maybe the coolant never gets below a certain temp? seems odd though.

Anyways, I started my car at 1:11pm, and around 1:15pm, my needle was dead center, and the temp reading was only 75C (so this shows you how much temp variation there is when the needle is dead center!)

In less than 10 minutes total time, my car was up to 95C and steady there the entire time I was driving, saw it go to 96 once and down to 94, but it stayed pretty steady at 95C.

I replaced my thermostat when I did the water pump around 100K I think. I am now almost at 170K.

Originally Posted by jfoj

DMAX, even if you were in 3rd on the highway, your temps should have still been a bit higher, HOWEVER, the thing that makes if hard for all of us to follow is if and when the DME has the thermostat heater activated??

My limited monitoring of my coolant temps with AutoEnginuity software shows that at about 3000 rpms the DME opens the thermostat.

The documentation I have seen from BMW indicates there are several factors as to when the DME opens the thermostat:

http://www.bmw-planet.com/diagrams/r.../e46/index.htm

With the aid of this thermostat it is possible to specifically increase the coolant temperature in the partial load range. By increasing the coolant temperature under these engine operating conditions, it is possible to reduce fuel consumption. This characteristic map thermostat is controlled by the engine control unit dependent on a characteristic map.
This characteristic map is determined by the following factors:
Engine load
Engine speed
Vehicle speed
Intake temperature
Coolant temperature

trizzuth,

Thanks for this input, looks very helpful.

As far as the engine coolant temp at start up, the engine will retain heat for a long time. Also depending on how much solar load is on the car, it may also keep the engine warmer for a longer period.

Usually you need to compare the engine temp after the car has been sitting overnight, but again the engine block and coolant mass take far longer to shift in temperature than say the ambient temp indicator under the bumper.

Your thermostat is looking typical at this point. How long ago did you replace your thermostat?

I am finding about about 3-4 years is when these stats start to get unreliable. I think the heated stats may have more issue as there is more than just a weak spring to give you problems, the heating circuits do open up, however, these usually hard fail and there is no guessing like a soft failing thermostat.

I must have replaced it around 4-5 years ago I am thinking..

I get to work around 9am, parked the car and it sat there till I left at 1pm for an MD appt.. 4 hours, but it was in the sun, and about 40+ degrees outside. I can see the sun warming up the engine compartment as I have Steel Grey Metallic, and the inside gets toasty even in 40 degrees if she's been sitting in the sun.

4-5 years is pretty good that your stat is still looking good.

I know my E46 had the stat replaced at about 4-5 years as I recall?

Maybe there are a lot more original thermostats still running in these cars?

Do not let Mango know if this is the case!

Originally Posted by WDE46

I just replaced my thermostat. I went from having a low of 66C on the highway at 80mph in 30F weather, to holding 95C in as low as 20F weather (I'm sure it will hold to even lower temps). Your operating temperature specs are most definitely correct.

As far as how long it takes to heat up, my car is in the center within 5-10 minutes of driving.

The low boundary on the buffered temperature needle is about 75C. If the needle is not DEAD center, then you have an issue. You could even have an issue if it is dead center, but if it's off at all, you DEFINITELY have a bad thermostat.

I also need to add that I had no error codes for a stuck or malfunctioning thermostat. I ran the car at that temperature 66C-75C on the highway for a month or two in 40 minute intervals. The error never appeared.

Just to add something really quick... my car runs at 95F all day long and the temp gauge sits slightly to the right. Maybe 1mm or less. This seems to be common on E46's I have seen on the internet. No problems here, just wanted to add that so you don't freak people out who are less well versed on these cars.

Originally Posted by ryannel2003

Just to add something really quick... my car runs at 95F all day long and the temp gauge sits slightly to the right. Maybe 1mm or less. This seems to be common on E46's I have seen on the internet. No problems here, just wanted to add that so you don't freak people out who are less well versed on these cars.

Eh yeah, you're right. You've got a little room to play with I guess. Not much though. I guess some needles are centered better than others.

Mine stays at 93c usually. After a period of hard driving, it creeps to 95 and then it cools right back to 93.

Here is a post from a week or two ago that might be able to help. If you need more logging let me know

Originally Posted by |2eckLesS

Before I begin this thread, I realize that all of what is about to be explained can be done with out the equipment used and would have been able to be accomplished with simple common sense. This is more of a shout out to JR at bimmersoftware.com

With that being said on December 8 I noticed that my 330ci was not blowing heat like I should be and the coolant temp was running low, averaging 21.9 MPG which is 50/50 highway city (no CEL thrown). As soon as I noticed this I started doing some research on options for diagnostics and data logging. I know this is kinda over the top for the tstat going out, but I figured this was a great way to get to know more about the car.

I had a day off this week and replaced the Tstat. 2004, 78K ZHP. Entire cooling system is going to be done this spring. Vanos, Plugs, and fuel pump are going to be first. After the new Tstat my MPG went up to 26.9 and same 50/50 (over 200 miles) and everything appears back to normal.

Just in case anyone was on the fence for this software, highly recommended because it is cheap, easy and strait forward, but gives you plenty of data to look at. (plenty more options to graph and 59.00 invested) Below is the before and after data log run. If you have any questions let me know. Hope this can help someone in the future.