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Anyone, I will strongly recommend that you don't waste time on replacing the inner seal. I have not seen any good arguments why this needs to be replaced and I have not found anybody who had problems because they didn't replace it. So if it looks fine, just leave it even if you have already bought a new one. Just my 5 cents on this issue...

Jesper
That's what I did. I have an inner seal for sale if anyone wants it!

--Peter
 

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Just finished this myself.

Here is another good reference:

http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/128936-thermostat-install-advice.html

I will add some notes:

1. I cannot imagine getting this done without removing once side of the VANOS oil lines. I removed the passenger side (US) which is one banjo and one hose clamp, and bent it up out of the way.

2. The difficulty with removal is caused by two factors:
1. there are two sliding 'joints' on each tube- one at each end. When pulling you get motion of both joints before one releases- if you could hold the tubes 'back' it would be easier- in any event, it takes fiddling. (To clarify- if each end has 1/4" of motion, it takes 1/2" overall to pop them loose. If you could ensure that only one part moves you can do it in 1/4". On disassembly you cannot control this- however on assembly, you place the tubes all the way in, so the final positioning is just that last 1/4".)
2. The end of the thermostat hits the bottom, fixed housing- If you can pry the old thermostat loose, and cant it slightly, this will give you a bit more motion to get that upper section out.

Assembly....

3. You MUST use lube. I used silicone o-ring lube for pool parts, plenty of stuff can be used. I was concerned with compatibility, but I think petrolatum (vasoline) should be good.

4. ALIGNMENT. Once you get it apart, try test fitting/inserting the tubes with o-rings into housing (out on your bench, in the light.) Get a sense of how this assembly should work: There is slight chamfer on the outer bore, and the oring- as it sits in it's groove on the tube- must contact this chamfer equally all around the circumference. Any 'tilt' to the tube (and the o-ring) relative to the housing/chamfer will cause the o-ring to push out - and get crimped or sheared off on continued insertion. If it is in equal circumferential contact as you push, it will go in and not get crimped

This is the key to the job. IMHO.

5. Grease up all o-rings. Grease up the housings on the engine and the thermostat housing. Carefully install the three tubes into the engine. FEEL for that alignment- gentle pressure- you will feel the tube 'line up' which indicates the o-ring is in circumferential contact- then gentle push. It should POP into place. Do this for all three tubes.
6. NOW that these three are into the bores, you can actually move these tubes- just a bit- upwards to get ready for the upper thermostat housing...

7. Next trick: Do not fully seat the thermostat into the upper housing- if it is loose, you can cant (tilt) it a bit to allow it's bottom part to clear the lower housing- BEFORE you need to engage all the o rings... you want to avoid trying to jam the o-rings in until it is all in perfect alignment.

So, place the upper part, loosely holding the thermostat in the housing let it tilt, then roate the upper part into the 3 tubes. Once you've gotten the upperhousing in place, you can get your fingers under and pop the thermostat up into it's final position.

8. Now take the time to align everything.... The upper housing should be pretty close to it's final 'mounting plane'- it is down, but maybe a few mm of compression left once you tighten the screws... but pretty much in it's final position vertically- take the three tubes and gently move them down to level- again feel the three tubes and their o-rings all pressing against their respective chamfers in the upper housing- gently but firmly, just ever so slight wiggle, and pop- in they go.

Bolt it up, all done.

A
 

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Parts List

I'm planning to take on this job soon and I'm looking for a definitive parts list. Here's what I've got so far:

08 Thermostat 79CEL 1 11537835558
07 Gasket ring 1 11531312287 x 1
09 O-ring 31X2,5MM 4 11531406249 x 4
11 O-ring 18,3X3,6MM 2 11531407002 x 1

Am I missing any O-rings? Lower temp sensor? I realize that some don't suggest changing the gasket ring, but that's another conversation.

Thanks!
 

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Hi Ard,

I noticed you are in the same area as me (I'm out in Cameron Park) and just did a thermostat install. I picked up a used M5 a few weeks ago and after driving it for a bit realized the temperature is probably running too cool. There are no faults in the computer, but with this cold weather we're having, the coolant temp is close to the first dot which after reading on the board for a bit doesn't sound normal. I'd assume you are seeing closer to the the middle of the range with the new thermostat even with the 30 degree weather around here? It sounds like some people are able to get this done quickly and some people are doing it over and over again with leaks. Do you recommend the DYI or should I consider taking it down to Valley Motorwerks? Car is an 03 with about 46K on it if that makes any difference.


Just finished this myself.

Here is another good reference:

http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/128936-thermostat-install-advice.html

I will add some notes:

1. I cannot imagine getting this done without removing once side of the VANOS oil lines. I removed the passenger side (US) which is one banjo and one hose clamp, and bent it up out of the way.

2. The difficulty with removal is caused by two factors:
1. there are two sliding 'joints' on each tube- one at each end. When pulling you get motion of both joints before one releases- if you could hold the tubes 'back' it would be easier- in any event, it takes fiddling. (To clarify- if each end has 1/4" of motion, it takes 1/2" overall to pop them loose. If you could ensure that only one part moves you can do it in 1/4". On disassembly you cannot control this- however on assembly, you place the tubes all the way in, so the final positioning is just that last 1/4".)
2. The end of the thermostat hits the bottom, fixed housing- If you can pry the old thermostat loose, and cant it slightly, this will give you a bit more motion to get that upper section out.

Assembly....

3. You MUST use lube. I used silicone o-ring lube for pool parts, plenty of stuff can be used. I was concerned with compatibility, but I think petrolatum (vasoline) should be good.

4. ALIGNMENT. Once you get it apart, try test fitting/inserting the tubes with o-rings into housing (out on your bench, in the light.) Get a sense of how this assembly should work: There is slight chamfer on the outer bore, and the oring- as it sits in it's groove on the tube- must contact this chamfer equally all around the circumference. Any 'tilt' to the tube (and the o-ring) relative to the housing/chamfer will cause the o-ring to push out - and get crimped or sheared off on continued insertion. If it is in equal circumferential contact as you push, it will go in and not get crimped

This is the key to the job. IMHO.

5. Grease up all o-rings. Grease up the housings on the engine and the thermostat housing. Carefully install the three tubes into the engine. FEEL for that alignment- gentle pressure- you will feel the tube 'line up' which indicates the o-ring is in circumferential contact- then gentle push. It should POP into place. Do this for all three tubes.
6. NOW that these three are into the bores, you can actually move these tubes- just a bit- upwards to get ready for the upper thermostat housing...

7. Next trick: Do not fully seat the thermostat into the upper housing- if it is loose, you can cant (tilt) it a bit to allow it's bottom part to clear the lower housing- BEFORE you need to engage all the o rings... you want to avoid trying to jam the o-rings in until it is all in perfect alignment.

So, place the upper part, loosely holding the thermostat in the housing let it tilt, then roate the upper part into the 3 tubes. Once you've gotten the upperhousing in place, you can get your fingers under and pop the thermostat up into it's final position.

8. Now take the time to align everything.... The upper housing should be pretty close to it's final 'mounting plane'- it is down, but maybe a few mm of compression left once you tighten the screws... but pretty much in it's final position vertically- take the three tubes and gently move them down to level- again feel the three tubes and their o-rings all pressing against their respective chamfers in the upper housing- gently but firmly, just ever so slight wiggle, and pop- in they go.

Bolt it up, all done.

A
 

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I replaced now three thermostats without removing the Vanos oil line,so it is possible;)
Just opended the clamps that hold the pressure containers in place and the it is quite easy...
 

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I'm planning to take on this job soon and I'm looking for a definitive parts list. Here's what I've got so far:

08 Thermostat 79CEL 1 11537835558
07 Gasket ring 1 11531312287 x 1
09 O-ring 31X2,5MM 4 11531406249 x 4
11 O-ring 18,3X3,6MM 2 11531407002 x 1

Am I missing any O-rings? Lower temp sensor? I realize that some don't suggest changing the gasket ring, but that's another conversation.

Thanks!
If that is the o-ring for the pipe going into the heat exchanger, you need 2, one for each end. I didn't do the end on the Tstat housing because it stayed firmly in place upon removing the Tstat housing.

Based on my experience, I would buy a couple extra of each o-ring, they are cheap enough and you don't want to have to make an extra trip to the dealer if you rip (or lose) one.

Regards,
Jerry
 

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Hi Ard,

I noticed you are in the same area as me (I'm out in Cameron Park) and just did a thermostat install. I picked up a used M5 a few weeks ago and after driving it for a bit realized the temperature is probably running too cool. There are no faults in the computer, but with this cold weather we're having, the coolant temp is close to the first dot which after reading on the board for a bit doesn't sound normal. I'd assume you are seeing closer to the the middle of the range with the new thermostat even with the 30 degree weather around here? It sounds like some people are able to get this done quickly and some people are doing it over and over again with leaks. Do you recommend the DYI or should I consider taking it down to Valley Motorwerks? Car is an 03 with about 46K on it if that makes any difference.
The gauge is not reliable. Use the information available in the dashboard computer.

d-
 

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Hi Ard,

I noticed you are in the same area as me (I'm out in Cameron Park) and just did a thermostat install. I picked up a used M5 a few weeks ago and after driving it for a bit realized the temperature is probably running too cool. There are no faults in the computer, but with this cold weather we're having, the coolant temp is close to the first dot which after reading on the board for a bit doesn't sound normal. I'd assume you are seeing closer to the the middle of the range with the new thermostat even with the 30 degree weather around here? It sounds like some people are able to get this done quickly and some people are doing it over and over again with leaks. Do you recommend the DYI or should I consider taking it down to Valley Motorwerks? Car is an 03 with about 46K on it if that makes any difference.
Indeed, same area. I'll look out for you.

So you had this issue, DID the thermostat, and it remains??? Please clarify.

In any event, the first dot is too cool- assumung the guage is working. As suggested above, unlock the OBC display and read coolant temp directly.

I cannot recommend DIY or not... all depends on the skills of the 'Y'. Valley has a good rep. I did not find the job to be hard at all.

A
 

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Indeed, same area. I'll look out for you.

So you had this issue, DID the thermostat, and it remains??? Please clarify.

In any event, the first dot is too cool- assumung the guage is working. As suggested above, unlock the OBC display and read coolant temp directly.

I cannot recommend DIY or not... all depends on the skills of the 'Y'. Valley has a good rep. I did not find the job to be hard at all.

A
Nope, just noticed the issue. I'm on the fence about whether to try the DIY or not, some of the stories in this thread and the other one were scaring me :2:

I wanted to make sure that the cold weather wasn't causing the issue, though if you're not seeing it with the new thermostat that's not very likely. I'll try the secret menu and see what the temp is, but unless I wind the motor up, it stays pretty much locked on the first dot. With some acceleration runs it will move a bit to the right but nowhere near the middle.
 

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Nope, just noticed the issue. I'm on the fence about whether to try the DIY or not, some of the stories in this thread and the other one were scaring me :2:

I wanted to make sure that the cold weather wasn't causing the issue, though if you're not seeing it with the new thermostat that's not very likely. I'll try the secret menu and see what the temp is, but unless I wind the motor up, it stays pretty much locked on the first dot. With some acceleration runs it will move a bit to the right but nowhere near the middle.
Classic worn Tstat; can check with OBC readout. Don't be scared, it is not hard, just a bit of a PITA.
Regards,
Jerry
 

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Classic worn Tstat; can check with OBC readout. Don't be scared, it is not hard, just a bit of a PITA.
Regards,
Jerry
Interestingly, Jerry, I don't think it is. My t-stat is brand new, tested before installation to open at 79C, and my temp gauge also sits at or about the left dot pretty much year round. According to my OBC, this is 78-79C. I've ordered a new temp sensor as I suspect this may be the issue, but then again it may just be that my car runs on the cool side of the allowable operating temperature range.

I'll find out if it is the sender in the next couple weeks, but til then, OBC is the only reliable gauge of operating temperature...

d-
 

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Classic worn Tstat; can check with OBC readout. Don't be scared, it is not hard, just a bit of a PITA.
Regards,
Jerry
Interestingly, Jerry, I don't think it is. My t-stat is brand new, tested before installation to open at 79C, and my temp gauge also sits at or about the left dot pretty much year round. According to my OBC, this is 78-79C. I've ordered a new temp sensor as I suspect this may be the issue, but then again it may just be that my car runs on the cool side of the allowable operating temperature range.

I'll find out if it is the sender in the next couple weeks, but til then, OBC is the only reliable gauge of operating temperature...

d-
 

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Interestingly, Jerry, I don't think it is. My t-stat is brand new, tested before installation to open at 79C, and my temp gauge also sits at or about the left dot pretty much year round. According to my OBC, this is 78-79C. I've ordered a new temp sensor as I suspect this may be the issue, but then again it may just be that my car runs on the cool side of the allowable operating temperature range.

I'll find out if it is the sender in the next couple weeks, but til then, OBC is the only reliable gauge of operating temperature...

d-
You may be right,cherrsagai I just didn't remember any posts with temp gauge at first dot and being temp sensor. When my car ran there, I was running around 74C. But your OBC shows correct temps.

But the sensor is a cheap part (under $20) so it is relatively easy to fix (and a heck of a lot easier than doing the Tstat!).
Regards,
Jerry
 

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Tons of posts lately on the replacing the Thermostat. I've been running at 76C consistantly for the past month (via the secret menu) and just scheduled to replace mine on Tuesday. I have no issues with performance but certainly gives me peace of mind as I'm approaching 100k miles and probably needs to be done.
 

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Interestingly, Jerry, I don't think it is. My t-stat is brand new, tested before installation to open at 79C, and my temp gauge also sits at or about the left dot pretty much year round. According to my OBC, this is 78-79C. I've ordered a new temp sensor as I suspect this may be the issue, but then again it may just be that my car runs on the cool side of the allowable operating temperature range.

I'll find out if it is the sender in the next couple weeks, but til then, OBC is the only reliable gauge of operating temperature...

d-
I searched a bit and found the Secret Menu instructions, is the coolant temp test 7 (which is described as Engine Temp)? When I activate that test, I see KTMP and a number but I don't know if this is coolant temp or some random engine temp sensor. I've seen some screen shots that show the word coolant in them, but none of the tests described have that listed. If coolant temp isn't test 7, which test is it?
 

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Its test 7 buddy. you have it correct.
 

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OK, just got back from a 40+ minute drive and I'm now thinking it's pretty likely the thermostat is going or gone. Here's what I saw based on Test 7 in the menu:

1) OBC KTemp sits about 72-73 C while cruising on the freeway at 80mph in 6th.
2) Stop and go driving, the temp jumps up to 75-78 C.
3) One stretch of road, the temp started climbing and actually got up to 81 C, but it didn't stay there very long.

Ambient temp is a little warmer now, roughly 55 F outside. Is this consistent with a bad thermostat? I wasn't expecting the range to be so big, so that is confusing me slightly.
 

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OK, just got back from a 40+ minute drive and I'm now thinking it's pretty likely the thermostat is going or gone. Here's what I saw based on Test 7 in the menu:

1) OBC KTemp sits about 72-73 C while cruising on the freeway at 80mph in 6th.
2) Stop and go driving, the temp jumps up to 75-78 C.
3) One stretch of road, the temp started climbing and actually got up to 81 C, but it didn't stay there very long.

Ambient temp is a little warmer now, roughly 55 F outside. Is this consistent with a bad thermostat? I wasn't expecting the range to be so big, so that is confusing me slightly.
Anything below about 78C after the car warms up means you need a new t-stat. Therefore, based on observation #1, you need a new t-stat. I'd guess that number 3 had you hitting the brakes and the accelerator on a regular basis, thus the higher temperatures.

d-
 

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Anything below about 78C after the car warms up means you need a new t-stat. Therefore, based on observation #1, you need a new t-stat. I'd guess that number 3 had you hitting the brakes and the accelerator on a regular basis, thus the higher temperatures.

d-
That's what I figured, but I got excited when I saw 81. Sadly, it didn't last. So once warm, it should never get below 78-79? I also noticed the exhaust smelled rich a few days ago after the car should have been warm, so all signs point to me getting my hands dirty soon. Glad I have a spare car :)
 
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