I'd recommend getting a fact check, the E39 M5 operating temp is 79C, around 11 o'clock on the analog dial, not 12 o'clock as on series BMWs. Don't chase a problem you don't have.

 

Complete part list for the job:

11537835558 x 1 (Thermostat)
11531312287 x 1 (Thermostat Sealing Ring)
11531407002 x 2 (Small O-rings - Thermostat Housing to Oil Cooler)
11531406249 x 4 (Large O-rings - Thermostat Housing to Cylinder Block Water Pipes)
07119963225 x 2 (Gaskets for Engine Block Drain Plugs)

I would order extra set of o-rings. (You might brake some of them during installation)

Last spring I had failed thermostat. Coolant temperature hardly went over 75degC in traffic and hoovered between 68...74 at highway speeds (70mph 6th gear / 18degC outside air temp). Traditional "stuck open" thermostat failure mode and subsequent overcooling with DME fault code 69 (Temperature plausibility).

It would be interesting to hear if anyone has experienced other thermostat failure modes. Especially, is it possible to have only partially opening thermostat and subsequent tendency to overheat?

 

I went through three behr / mahl thermostats. The last one lasted less than 5k miles before I started getting a car that would sound like yours is acting. I'm not alone, there are numerous threads of people like me that needed to change them out at oil change intervals. I drive mine through winter/dd and if I was coming down the mountains in the cold it would drop down to the left dramatically. Well into the warm up zone. If the thermostat has truly failed, you should eventually get a corresponding error code come up. I could tell from the massive amounts of soot that would form on the back of the car as well as the needle action before I got the error code.

Since I went with the "stant" thermostat (knock on wood), I haven't had a failure in the last 10k miles. There are threads on this board about the stant (I believe that was the manufacturer). The stant was around 20$ if memory serves correctly and it didn't fit exactly right. It needed some permatex to fill the gasket gap. It does work though and continues to be my current record holder.

DIY's are in the stickys up top. The O rings do not always have to be changed. If they are relatively newish, changing them out is a waste of time money and effort although you will get those who will say it needs a new motor now because you changed out the thermostat.

 

Relatively recent clip in YouTube:

https://www.youtube.com/watch?v=t6qrUkYourI

 

Well, I am not getting a CEL and no more soot out the back than I've noticed before. I got out my Peake reader - no codes pulled, definitely no code 69.

Should I expect the temp needle to move while driving? I'm not used to that behavior out of any car - including the E36 M3 I had previous to this car. All my previous cars the needle moves up to it's usual spot and stays there. Or is it just that this is the biggest engine I've ever owned and it takes much longer to warm up than I think it should?

 

Monitor actual temps on the OBC. #7. The gauge is not terribly accurate. If you can keep 79 C on the highway (=/-1 degree), I would say the tstat is fine.

Regards,
Jerry

 

Just check the actual temp from the DME (through secret menu, intravee (on nav), computer software, etc.) The ECT should warm to at least the rated thermostat temp (stock is 79* C) within 5-10 minutes and never come back below that temp during operation. You will typically have a code the peake can read if you have failure, not always though (I had 69 when mine failed). I would also advise to steer clear of the OE/Behr stat when replacing. They seem to not last as long as others. There are replacements available from Gates, Stant and many others for $10-20. Gates and Stant, in my experience, make very high quality parts which are OE level or better (my car has Gates belts and a Stant thermostat, blasphemy...) I replaced my failed stock BMW/Behr with a Stant 82* C and it is working great.

 

My gauge also tends to sit around 11 o'clock position. I agree with Jerry... get the actual temperature readout off the OBC readout before you go replacing the tstat.

 

Looks like I need to figure out the secret menu. It's something I haven't messed with yet. I'll report back with findings. Thanks for all the help so far.

 

Here’s how to unlock the test modes in the dashboard cluster:


1) Key to ignition pos 2 (no need to start engine).
2) Fasten the seat belt to get rid of the “Fasten Seat Belt” message.
3) Press the right button on the instrument panel, and hold it until “TEST-NR. 01″ comes up (5 to 10 seconds).
4) Press the left button on the instrument panel, and the vehicle id comes up (last 7 digits of VIN).
5) Add up the last 5 digits to get the “unlock code”, e.g. the unlock code for “AB12345″ would be 15 (1+2+3+4+5).
6) Repeatedly press the right button until “TEST-NR. 19″ appears.
7) Press left button -> “LOCK : ON”
8. Repeatedly press left button until “LOCK : xx” appears, where “xx” is your unlock code.
9. Press the right button. All modes are unlocked now.


Regards,
Jerry

 

Regarding your original question: My personal experience has been 2 Behr units and 1 OEM from BMW. All 3 look exactly the same and say Behr on it and have the same manufacturing numbers on them. So don't waste your money on OEM. I had to do it once just to see for sure myself. That one is still in my car. I just checked my records and I changed it last November, so now will be my time to check and see if it's still working. I've been getting about a year, year and 6 months out of a thermostat so far. That equates to approximately 20-25,000 miles each.

I've heard good things about the Stant thermostats so far, although as stated it's not 100% exact fit (which is no big deal) and it's not a 79* opening, it's 82*.

 

:nono:

:Thumbdown:

How many times do we have to go through this?

First off, if you can't afford to properly maintain supercar then you probably shouldn't own a supercar. Cutting corners to save a few bucks at the cost of damaging their car, it is all quite unseemly :nono:

I mean, is saving $30 on a thermostat for an inferior product appropriate? I think we all know the answer to this.

Just because it is made by the same manufacturer and looks the same and might even be stamped with the same markings, THIS DOES NOT MEAN THAT IT IS THE SAME.

OE parts sold originally sold with the car are obviously the best. The next step down are OEM parts sold BY A KNOWN SOLID BMW DEALER bought at full retail price (if you are paying less than full price you are probably getting old stock or parts that are somehow not as good as the full price ones, remember - you get what you pay for).

OEM parts bought from other sources are questionable for the reasons noted above. In addition people have reported that parts sold by OEM manufacturers through other channels ARE NOT of the same quality as the parts sold by KNOWN SOLID BMW DEALERS sold at full retail.

Next down the rung are non OEM parts but do we really even need to talk about these in the context of a supercar? I didn't think so.

 

Rao, you're getting almost TOO good at the replies to these type of questions. I even found myself falling into the trap for the first sentence or 2................................. wait.................it wasn't a trap?!?!??!?!hiha

Last time I replaced my OE dealer supplied stat I did so after about 10K and I think it was down to the fact I got discount through being a forum member. My latest stat I actually rang around dealers asking if they ever marked stock up and would they be willing to on this thermostat.

I found one dealer who was willing to charge 50% over RRP and bought and installed that. Since then as of yet my car has ran nicely up to temp with no issues.

Coincidence? No I didn't think so.

 

Jamie, can you please send me PM via M5board and include your private email address so I can answer back. I'm still under that (IMO strange) 45-postcount rule and I can't send PMs. I have some news for you.

 

I unlocked the secret menu and will drive the car in a bit.

Do I have to go through the whole unlock sequence every time I drive the car, or will the car remember that it's been unlocked? That's tedious if it must be done every time...

 

It ony needs to be done again if the battery is disconnect in my experience.

 

Got it.

Short drive was all I had time for today. Ambient temps were low 60s F, so I don't know what it'll do when it's actually cold, but 15 minutes in stop-and-go traffic saw the car warm up quickly; once it was "stabilized" it went to a low of 77*C while coasting and a high of 85*C while sitting at a long stoplight. This seems like pretty predictable behavior. I'll have to take some readings my next time on a freeway.

The water temp needle waved around again during this time though - as described in my OP. No idea why.

 

Got it.

Short drive was all I had time for today. Ambient temps were low 60s F, so I don't know what it'll do when it's actually cold, but 15 minutes in stop-and-go traffic saw the car warm up quickly; once it was "stabilized" it went to a low of 77*C while coasting and a high of 85*C while sitting at a long stoplight. This seems like pretty predictable behavior. I'll have to take some readings my next time on a freeway.

I would say you are borderline low. 79 plus or minus 1. Do another highway run, steady for 5-10 minutes, see what happens when you go to full heat for 30 seconds to 1 minute. Then go back to normal temps. Keep an eye on the OBC temp.

The water temp needle waved around again during this time though - as described in my OP. No idea why.

Could be an issue in the gauge itself. There is a smoothing program so the needle doesn't move much on purpose. I wouldn't worry about the gauge if you can monitor actual temps with the OBC.

Regards,
Jerry

 

There are two sensors I believe. One on the radiator ( I think where the hose connects on the low end ) and one on the top of the water pump where the upper radiator hose connects. I would be very interested what your readings and needle movement are after you wire brushed the inner brass ends of those two sensors and pulled the plugs on and off a few times to make sure the connections are clean.

Does your electric fan (front of radiator) kick on after getting into 84?

I wouldn't buy any parts until after you confirmed the ones you have are clean and working.

 

Going to have to start troubleshooting myself. From what I've seen my temp seems to dip down to 74C when cruising on the highway more than 5 minutes.

What is the typical range for oil temp? Here are some numbers I see:

City
KTemp: 79C
Oil: 88C
Ambient:77F

Highway
KTemp: 74C
Oil: 84C
Ambient: 77F

Spirited
KTemp: 80C
Oil: 91C
Ambient: 77F

There's some elasticity between Ktemp and oil temp lately. I'm getting worried my oil is running too hot on warmer days, sometimes it gets up to 92C in city driving with 85F weather, and Ktemp 82. Oil was changed 200 miles ago.

 

You need to replace the thermostat. ECT should always stay above 79° C.

As for oil, the safe operating range for oil is about 80-120° C. 120° C would be very very hot and only acceptable on a hot track day and I would change after. But it's not out range in my mind. For a street driven car, probably no more than 105-110° C.

 

I'm seeing similar behavior on my Ktemp. On my 35-mile drive home yesterday (mostly country and highway) ktemp bounced between 74 - 81C. Most of time around 77-78C. Ambient temp of 17C and light traffic while on the backroads.

Is this what you would call a typicall partial stuck open symptom? I also get no codes when I run INPA diagnostics. How does the DME respond to temps below 79C, a richer run mode/warmup?

 

I'm seeing similar behavior on my Ktemp. On my 35-mile drive home yesterday (mostly country and highway) ktemp bounced between 74 - 81C. Most of time around 77-78C. Ambient temp of 17C and light traffic while on the backroads.

Is this what you would call a typicall partial stuck open symptom? I also get no codes when I run INPA diagnostics. How does the DME respond to temps below 79C, a richer run mode/warmup?

Yes. That is why it is not an emergency, but it should be addressed. Once you hit 79, you should be able to stay within 1 degree. If you drop to 74, tstat is sticking open based on the collective experience here.

Regards,
Jerry

 

Hi - I think I also have a partially stuck open thermostat as well. Picked up a new one from the dealer for £70ish pounds sometime back and inquired how I claim on the 2 year warranty as the last BMW supplied OEM was only fitted 22 months back. Disappointed to hear the warranty is not worth jack unless it's all done by the dealer OR checked out and analysed by the dealer as a problem at your cost until they prove it's a defective part. This is UK - in US and elsewhere you may get a much better service - it would not surprise me.

Had an interesting discussion with the parts guy when he said they can pop it on their clever computer and get it diagnosed quickly - only way I can think of proving this part defective is to put it in a pan of water with a thermometer old school style! Personally i've seen what the average dealer service agent is like and trust my car to a friends independent garage with proper mechanics rather than parts changers so to me the warranty is a waste of time. Next time i'll be fitting a £30 euro car parts Wahler part instead.

Simon

 

The thermostat design in this engine is "unique". It's not super special, it's used in caterpillar diesels and the S85 and probably many other cars. But the easiest way to describe it is that there are two water paths and the thermostat controls (infinitely variable) which path the water takes. There is a seal between the two paths. The seal gets old, looses its sealing and lubrication properties and causes the thermostat wall to stick. If you pull it out and put it in boiling water this friction from the sealing ring isn't there and it may work just fine even though the spring and wax element may be weak. I am not kidding when I say these cost $10-20. It's $10-20. Don't waste time testing or dealing with BMW to warranty a part that as stated above may be a huge headache. Buy a new one. Spend the afternoon installing it. Your car will thank you.

 

I've bought a new seal as well as I guess mine is original - people report it can be a bit of a pain to remove - anyone have any tips above all the usual seal puller? I have a hook type one.

Simon

 

I finally had the time to do a highway run this afternoon after work. I wish I drove the car more, but it's not my daily and work/family claim first rights to my time...

I drove about 35 minutes on the highway. 15 minutes out, hit a drive-through for a Coke, and 15 minutes back. I set the cruise at 70mph the whole way and ambient temps were in the 60s F.

On the way out I set the climate control at 65*. The car took a few minutes to get up to temp but then stayed rock-steady between 79* and 78*C, only dipping to 77* on one particularly long downhill section of the road where the engine has much less load.

In the drive through the temp spiked to about 85*C and then it was back on the highway. This time I turned the heat up all the way to 90* and the fan about 2/3 of maximum. Tellingly, the coolant temp did EXACTLY the same thing as it did on the way out, when the heat was off - mostly stayed at 79* or 78* and never went to 77*.

Temp rose again in the stop-and-go between the highway and home and was about *88 when I got into the driveway. I took the opportunity to verify that the electric fan had kicked on.

At this point I'm going to declare the thermostat in my car OK though I will be monitoring things closely as the weather continues to turn cold. The temp gauge on the dash continued to waggle around, for which I have no explanation. Most of the other cars I've played with have had only two sensors - a two-wire sensor for the ECU and a single-blade arrangement for the gauge in the dash. I have no idea where the M5's gauge gets its reading or even if it's been modified to move around more in my car (I know there's a way to do this in the E36 M3).

I'd be grateful for any other input but for now I'm not planning to change the stat. Thanks for all help.