540i Lower Temp Thermostat - Best Option?

[gjVah]

Hello everyone, I've been absent on BFC for quite some time now, due to lots of work and not enough free time. I have been recently looking into switching my thermostat to one that operates at lower temps, and after reading a lot of threads on the subject, it seems everyone who has done this "mod" is happy with it. However there doesn't seem to be a consensus on what the best one to get is (80c vs 87c and even 75c), and the newest information I was able to find is more than a couple of years old. So my question to those who have done this, (especially the guys with the TU engine, since my car does have Vanos, 99' model) is: what part did you use, and was it a direct bolt on? Second part of the question: Since there were some people advocating against doing this, have you had any issues that you think are directly related to this mod.

Thank you for your time.

[BMW540san]

Since you say you've read about it, I won't turn this into a novel but few points:
For M62TU, 88C conventional thermostat that I've sold here is the only truly direct fit with slight modification of adding resistor to disconnected thermostat wiring.
While few had issue with codes due to colder thermostat, majority had no problems whatsoever.
I'm running non vanos 95C from older M62 on my X5 4.6is M62TU which required some modifications but nothing competent DIY can't handle it.
If I didn't have already when I discovered 88C source where I got bunch for decent price, I'd be running it on my X5.

[gjVah]

Since you say you've read about it, I won't turn this into a novel but few points:
For M62TU, 88C conventional thermostat that I've sold here is the only truly direct fit with slight modification of adding resistor to disconnected thermostat wiring.
While few had issue with codes due to colder thermostat, majority had no problems whatsoever.
I'm running non vanos 95C from older M62 on my X5 4.6is M62TU which required some modifications but nothing competent DIY can't handle it.
If I didn't have already when I discovered 88C source where I got bunch for decent price, I'd be running it on my X5.

So there is no actual plug n play part that won't throw any codes? I was looking at this one, I also saw it mentioned in a few other threads. http://abbes-performance.com/bmw-lan...emperature-80c

Last questions: Besides it being the most "direct fit" is there another reason one would go with the 88c vs 80c? Also, do you still sell the 88c part or am I late to the party?

[1999 540i m]

I have 2 of the behr 88c stat's very happy with them, another option is this https://www.ecstuning.com/b-vemo-par...512248542~vmo/ , and this http://www.bmwlogicseven.com/?cat=151 this one has the connector

[geargrinder]

Too cold is not good, even though a lotta knuckledraggers think "you can't have cold enough" and "high temps are only for emissions!". But engines run w/ less friction at higher temps which means less wear and more performance. so you really want to shoot for a sweet spot which is something around the 90's Celsius (the 88C T-stat means the engine runs generally in the low/mid 90's most of the time). 80C is frickkin cold prob not a good idea. There's even an argument that 88C is real cold - ie something like 'san's 95C or a 92C are the kind of thing that most BMW M motors get from the factory.

The 88C is closest to plug and play for sure, but you need to make a resistor to fake the DME into not throwing a code because the 88C has no plug on it and the DME wants to see "oh there's a thermostat connected". But its' pretty easy no-brainer. Single power resistor, zip tie it under the beauty cover, easy.

Some later cars - seems like the 2002's specifically - seem to have DME software versions that will throw an SES occaisionally w/ the 88C because the DME is smart enough to notice "Hey! WTF! This engine is running too cool!" but seems like that's mainly just a subset of later cars.

[gjVah]

I have 2 of the behr 88c stat's very happy with them, another option is this https://www.ecstuning.com/b-vemo-par...512248542~vmo/ , and this http://www.bmwlogicseven.com/?cat=151 this one has the connector

Hi, thanks for the links. Does getting the one with the connector mean I won't get any codes, or is it simply to avoid using a resistor? Another point for me to consider is the temp gauge. I recently put on an M5 cluster, that I have yet to code to the car. As I'm sure you know (judging by your sig) the M5 runs cooler, hence my temp gauge is pegged to the right. If I were to use the lower temp thermostat, would that mean that I wouldn't need to have that particular gauge re-calibrated? This is the one thing I have to figure out before I send in my cluster, since I don't wanna send it twice, in case the new temps make my gauge read lower than 12 o'clock. I hope this makes sense.

- - - Updated - - -

Too cold is not good, even though a lotta knuckledraggers think "you can't have cold enough" and "high temps are only for emissions!". But engines run w/ less friction at higher temps which means less wear and more performance. so you really want to shoot for a sweet spot which is something around the 90's Celsius (the 88C T-stat means the engine runs generally in the low/mid 90's most of the time). 80C is frickkin cold prob not a good idea. There's even an argument that 88C is real cold - ie something like 'san's 95C or a 92C are the kind of thing that most BMW M motors get from the factory.

The 88C is closest to plug and play for sure, but you need to make a resistor to fake the DME into not throwing a code because the 88C has no plug on it and the DME wants to see "oh there's a thermostat connected". But its' pretty easy no-brainer. Single power resistor, zip tie it under the beauty cover, easy.

Some later cars - seems like the 2002's specifically - seem to have DME software versions that will throw an SES occaisionally w/ the 88C because the DME is smart enough to notice "Hey! WTF! This engine is running too cool!" but seems like that's mainly just a subset of later cars.

Thanks for the info and insight. And yeah, I know what you mean, I'm not looking to run super low temps, just a little bit lower. It gets really hot in the summer here in LA.

[1999 540i m]

Hi, thanks for the links. Does getting the one with the connector mean I won't get any codes, or is it simply to avoid using a resistor? Another point for me to consider is the temp gauge. I recently put on an M5 cluster, that I have yet to code to the car. As I'm sure you know (judging by your sig) the M5 runs cooler, hence my temp gauge is pegged to the right. If I were to use the lower temp thermostat, would that mean that I wouldn't need to have that particular gauge re-calibrated? This is the one thing I have to figure out before I send in my cluster, since I don't wanna send it twice, in case the new temps make my gauge read lower than 12 o'clock. I hope this makes sense.

The one with the connector is an oem unit that has been recalibrated, so no code from that, maybe the occasional low temp code that some get, I don't know.

As far as the m5 cluster, 88c is really close to the 85c of the m5, my total guess is that it would fix the off center needle

[gjVah]

The one with the connector is an oem unit that has been recalibrated, so no code from that, maybe the occasional low temp code that some get, I don't know.

As far as the m5 cluster, 88c is really close to the 85c of the m5, my total guess is that it would fix the off center needle

Thanks for the help, will order the one with the connector.

[geargrinder]

OK. Two items.

So the cluster stuff is entirely different. That oil temp gauge is what youre talking about right? The one centered below the tach? That's oil temp not coolant. And it displays a temp that's sent over the CAN bus. The M62TU DME (as opposed to the S62 DME) doesn't send the oil temp over CAN (without mods that is and if it is not a 4.6 or Alpina etc). So for reasons I forget the cluster gets coolant temp instead and for some scaling reason I guess it pins the gauge. So that's the thing that needs fixing and it isn't fixed in the cluster coding it is fixed in the DME Tune - Terraphantm made some OEM modded binaries people could flash as long as you weren't tuned or otherwise special.

The actual coolant gauge is the one on the far right. That one you CAN recalibrate w cluster coding. You can code that same as M62 stock (so an 88C would read a bit low) but I have custom coded mine for 88C also, I have a thread on that somewhere. Works great. Mine is now straight up around low 90's (which is what an 88C stat gives you really)

Then - as to the "recalibrated" thermostats. Well. Ok. That dudes page is full of kooky rants and minor misinformation and misconceptions, but ok fine, leaving that aside... I'm fairly sure his "recalibration" is the same trick our own JimLev pioneered a while back which consists of heating the OEM spring w a torch to soften it and reduce its tension. Again...OK. Jim proved it works and for a homebrew mod, great. BUt I wouldn't call it "calibrated". The only way to "calibrate" would be to buy 90C or whatever springs and swap them into stock housings. Sadly you can't disassemble the OEM "plug" type thermostats without screwing them up, otherwise we'd all do that, which is why it's pretty certain that that guy is torching the OEMs to 'recalibrate'. Personally I'd not waste money paying some guy to whack a torch on a spring and pretend he was selling me fancy calibration, I'd just do it myself. But ultimately I'd rather have a proper factory and actual 'calibrated' Tstat so in my book the 88C w the resistor is the way I prefer to go.

[philly98540]

Agree. Get the 88. Do resistor.

[BMW540san]

The one with the connector is an oem unit that has been recalibrated, so no code from that, maybe the occasional low temp code that some get, I don't know.

As far as the m5 cluster, 88c is really close to the 85c of the m5, my total guess is that it would fix the off center needle

Slight correction here.
M5 thermostat open at 79C and it's specifically designed for M5 engine.
If we were even able to modify M62/TU engine to run it, that would be about worst thing we could do for it.
79C is waaaaay to cold for M62/TU overall health.
88C is borderline cold depending on climate but it's better than 105C which besides being closer to dangerous temp, it also produces more pressure on cooling components.
More heat = more pressure.

- - - Updated - - -

OK. Two items.

So the cluster stuff is entirely different. That oil temp gauge is what youre talking about right? The one centered below the tach? That's oil temp not coolant. And it displays a temp that's sent over the CAN bus. The M62TU DME (as opposed to the S62 DME) doesn't send the oil temp over CAN (without mods that is and if it is not a 4.6 or Alpina etc). So for reasons I forget the cluster gets coolant temp instead and for some scaling reason I guess it pins the gauge. So that's the thing that needs fixing and it isn't fixed in the cluster coding it is fixed in the DME Tune - Terraphantm made some OEM modded binaries people could flash as long as you weren't tuned or otherwise special.

The actual coolant gauge is the one on the far right. That one you CAN recalibrate w cluster coding. You can code that same as M62 stock (so an 88C would read a bit low) but I have custom coded mine for 88C also, I have a thread on that somewhere. Works great. Mine is now straight up around low 90's (which is what an 88C stat gives you really)

Then - as to the "recalibrated" thermostats. Well. Ok. That dudes page is full of kooky rants and minor misinformation and misconceptions, but ok fine, leaving that aside... I'm fairly sure his "recalibration" is the same trick our own JimLev pioneered a while back which consists of heating the OEM spring w a torch to soften it and reduce its tension. Again...OK. Jim proved it works and for a homebrew mod, great. BUt I wouldn't call it "calibrated". The only way to "calibrate" would be to buy 90C or whatever springs and swap them into stock housings. Sadly you can't disassemble the OEM "plug" type thermostats without screwing them up, otherwise we'd all do that, which is why it's pretty certain that that guy is torching the OEMs to 'recalibrate'. Personally I'd not waste money paying some guy to whack a torch on a spring and pretend he was selling me fancy calibration, I'd just do it myself. But ultimately I'd rather have a proper factory and actual 'calibrated' Tstat so in my book the 88C w the resistor is the way I prefer to go.

Well said!

[Mannyf540]

Too cold is not good, even though a lotta knuckledraggers think "you can't have cold enough" and "high temps are only for emissions!". But engines run w/ less friction at higher temps which means less wear and more performance. so you really want to shoot for a sweet spot which is something around the 90's Celsius (the 88C T-stat means the engine runs generally in the low/mid 90's most of the time). 80C is frickkin cold prob not a good idea. There's even an argument that 88C is real cold - ie something like 'san's 95C or a 92C are the kind of thing that most BMW M motors get from the factory.

The 88C is closest to plug and play for sure, but you need to make a resistor to fake the DME into not throwing a code because the 88C has no plug on it and the DME wants to see "oh there's a thermostat connected". But its' pretty easy no-brainer. Single power resistor, zip tie it under the beauty cover, easy.

Some later cars - seems like the 2002's specifically - seem to have DME software versions that will throw an SES occaisionally w/ the 88C because the DME is smart enough to notice "Hey! WTF! This engine is running too cool!" but seems like that's mainly just a subset of later cars.

After having my thermostat for about 2 years I got an SEE light. I scanned it, no codes. Kinda dumbfounded, why did it not throw the code the first year? Perhaps it has another issue that triggered the SES. Although it does not jump of the line like before, maybe a vacuum leak.

[gmak]

I don't think that the different temperature thermostats work based on the mechanical characteristics of the respective spring. I believe that they work based on the type of wax inside the thermostat. Wax expands as it liquifies and, IIRC, that is what pushes the thermostat open.

The standard 540i thermostat with the DME control would operate mechanically i.e. let temperature get high. When the DME signals the thermostat to open (because it's program says that the engine should run cooler) , it is actually providing heat via resistance to melt the wax - i.e. it works to keep the engine cooler. When there is no signal melting the wax, then the thermostat works mechanically. I don't know enough about the DME program to say when it wants the engine cooler and when hotter - but it does seem to make sense that it would run higher in traffic in order to get the mpg up to meet standards.

Since modifying the spring works as has been clearly demonstrated, I will just say that it is only because the mechanical characteristics have been changed to provide less counter force, so that the wax melting is able to push open the thermostat sooner than it would were the spring left alone with its original characteristics. Is this mechanical alteration to the spring permanent? Will it remain constant over time? That is hard to say without empirical data and the response curve of the modified spring to applied force.

All this blah blah blah is to say that the behaviour of the mechanical 88C thermostat, and the modified thermostat will be different (if the modified one does still work off of the DME signal). When the wax is melting inside the spring-modified thermostat- i.e. due to high engine temperature - the spring will open sooner and more due to its weakened structure. But the signal from the DME will still be in keeping with the programming - so there will tend to be higher temperatures under certain operating conditions, and lower temperatures under others. With the 88C thermostat, the temperature of the engine will be determined by purely mechanical conditions - so higher temperature, more cooling through a greater opening.

On the other hand, If the logic7 thermostat is really a mechanical one with a plug that does nothing except fake out the DME - then it's the same as the 88C but 2 degrees warmer.

[gmak]

I'm curious, so I asked the BMW Logic7 guys these questions:

Question: Do you modify the spring, or is the wax inside the thermostat rated for a lower temperature? Does the thermostat respond to the DME, or is the plug just a resistor to avoid the errors?

[philly98540]

Yes, the exact melting temp of the wax is what sets the temp of the stat. They use different waxes for diff stats is what I remember reading.

[geargrinder]

All true Gman but Jim and others have proven - since it's a "spring Vs wax" contest the spring trick can work , whether it's the way the factory ones are calibrated or not (and for non MAP ones remember the wax heats up via coolant and so it's almost immaterial whether you have a lighter spring or a faster expanding wax... I really doubt they are siphoning out wax and refilling somehow.

[dannyzabolotny]

Meh, I run a stock thermostat in 120°F weather and I'm fine. Temps never go past 105°C even when I'm beating on it. Replace your expansion tank and radiator every few years and you'll be fine.

[geargrinder]

Agree in a way sorta. Kinda relates to my "visco delete works fine" posture.

But... lower temps and pressure are clearly good for wear and tear and longevity etc in these bitches.

I'd say these mods aren't must dos, and for civilian "just pay the mechanic don't understand the car" types, I wouldn't ever confuse those people w the details. However if you like tinkering and modding and like the idea of destressing the system and can roll with potential funny business... (CEL/MIL/SES can be huge hassles for certain states inspections and if you're there then maybe you want to be more cautious) then it's worth considering and is a 'good' mod.

[Texasdeere]

Just my experience Non Vanos engine:

1998 540i with M62B44, Replaced thermostat with E31 Gulf climate option 85C. So far no codes or lights for the lower temp or the unplugged wire. Car now runs at 90C or about 194F used to run 226F according to OBDII scans. I also replaced the rad cap with a 1.4 bar cap and installed an 80-88C small pin fan switch from a 3 Series. Cooling fan has never come on yet as the engine driven fan seem to work very well. All OE parts.

[philly98540]

^can you post part number on that switch?

[geargrinder]

Just my experience Non Vanos engine:

1998 540i with M62B44, Replaced thermostat with E31 Gulf climate option 85C. So far no codes or lights for the lower temp or the unplugged wire. Car now runs at 90C or about 194F used to run 226F according to OBDII scans. I also replaced the rad cap with a 1.4 bar cap and installed an 80-88C small pin fan switch from a 3 Series. Cooling fan has never come on yet as the engine driven fan seem to work very well. All OE parts.

Sounds about right. Except the cap. That's a dumbass misguided move. Everything else is fine tho and as it should be.

[Texasdeere]

http://www.realoem.com/bmw/enUS/show...diagId=11_4950

85 GRAD Thermostat for E31 11531742964

Double Temperature Switch 80/88CEL 61318376440

I am fairly certain on these part numbers as I have thrown away all the receipts and the boxes are 100 miles away.

Sounds about right. Except the cap. That's a dumbass misguided move. Everything else is fine tho and as it should be.

Just trying to protect an old original radiator. The cap was easy. 1.4 is still 20 psi, still a lot higher than the average car that runs 195F . So far steady temps and no boil over or seepage. I assume these cars have no overflow tank?

I can't figure out the Behr 1.4 cap p# pretty sure it was for an E30 Looks like some are trying a 1.2 bar in some other posts.

I don't drive my car very hard and I think that may be why I don't have a light or code yet as the heating element is probably never energized? Or I just have an older operating system in an earlier production 98 540? I think most cars get at least a soft code.

I apologize in advance if I am not supposed to post any outside links in posts but I stumbled upon this a while back and might be a good thermostat option for some?

http://www.bmwlogicseven.com/?tag=coller-thermostat

[geargrinder]

Yes you probably have early software that might not throw codes... There's the 2 codes people see - one for being disconnected that generally doesn't throw a SES light, and one that is for 'temp too low' that will throw the light. Seems like its' 2002 or later software that does the latter.

Re: the caps - I was being harsh in my wording but all that stuff including whatever E30 guys are doing is almost always fully based on a fundamental misconception of the purpose and scenarios surrounding the cap pressure.

It does not 'set' the pressure in any way shape or form. However it seems 90% of laymen think it does - and that's what even a lot of seller websites are happy to play upon in order to make money off them even though they certainly know its a load of BS.

The cap is purely an over-pressure device to keep the radiator and/or hoses from exploding when the engine severely overheats. Period. It does nothing else but act as the safety-valve just like the same over pressure valve on your house's water heater.

And high pressure in the radiator is normally good - it raises the boiling point, which is why all cars have pressurized radiators now.

The cap pressure should be something that under normal conditions occurs only after you've already hit engine-endangering temperatures.

You'd generally rather explode a radiator or hose first due to high pressure, than to warp a head or have some other damage due to overtemp.

The extreme low pressure cap - say the 1.2b that some guys have claimed to use - scenario is
1. engine starts to overheat for some reason - ex: fan failure
2. temps rise and pressure rises to cap level although engine is still in the "OK" zone
3. cap vents coolant
4. suddenly system water volume is reduced, and pressure reduced
5. due to reduced pressure boiling point goes down, more steam created, more water vented
6. lather rinse repeat etc. and a 'thermal runaway' and bad things potentially happening to your motor

In that same case, with the stock cap, the cooling system very well might have recovered and not gotten to the 3-4-5-6 stages.

Furthermore, you can do the math on the pressure/temp correlation and think the 2.0B factory cap might sound like overkill.

Well that's because coolant temps / pressure can spike after shutdown, and a common problem with the low pressure caps is that they vent a little coolant when the car spikes after shutdown in super hot in hot weather. Then when you return you have less coolant, lower pressures, higher boiling point, next time it happens again, then it happens again etc. With the M62 operating normally up as high as 115C you can imagine a spike on top of that...

Bottom line 2.0B caps are not a problem whatsoever and lower PSI caps are not fixing anything.

If you DO want to have lower pressure-related stress on your cooling system however, there IS a fix that definitely does that. Evans waterless coolant. Operates at zero pressure atmospheric, in fact most guys leave the cap loose. That WILL dramatically reduce / eliminate system pressure in your engine. Philly here uses that and loves it.

[54ODell]

Will the lower thermostat allow the ECU to increase timing too or is that based on intake air temp instead?

[geargrinder]

Doubtful it would really allow an 'increase' in timing.

Usually it's IAT that drives the tables. What engine temp may help with is slightly reducing charge temps from engine heat, and from generally NOT getting detonation at the knock sensors due to lower engine temp, so it may well avoid getting a timing PULL... Not exactly the same, but still a bonus. You might have noticed these VF setups without meth heat soak after 2-3 consecutive pulls and you need to cool down for a minute or two before you're back to 'full powah'. Kinda seems to me like maybe I get less heat-soak timing-pull effect now that I'm on the cooler t-stat however I'll quickly admit that very well may be placebo butt dyno wishful stinking.