Looking for Resistor part number for 88C Thermostat!

[mjrgroup]

Different versions of the DME firmware will produce different results when removing the thermostat heater circuit. The latest 2003 software won't set a CEL or OBD2 code for the missing heater circuit but will set an internal DME code. But it will set a CEL for P0128/coolant temp too low if you don't properly reprogram the DME for the lower operating temp.

How can you reprogram the DME? Do you use INPA or could something like an Aurel work? Or something more specialized?

[ThePhantom!]

To update this thread, I finally got the 88C thermostat from ECS. It took 2 months to arrive!

Yesterday, I replaced the 105C tstat with the 88C tstat successfully. The resistor worked perfectly, no codes on the cluster. I proceeded to top off the expansion tank with coolant after loosing quite a bit of coolant during the install. I bled the cooling system too.

Now, I do have some questions about coolant temp....

This morning I bled the cooling system again just in case. To bleed the cooling system, I put the key into the ignition, turned the fan on max heat, started the engine with the bleed screw loose and expansion tank cap off, added coolant (50/50 pre-mix), revved the engine to 1500-2500rpm, and then at the 4 minute mark, I put the cap back on, completely removed the bleed screw and revved it more to get rid of any last air, and then screwed it back in and turned the car off.

Soon after, I took the 540i out for a drive for about 45 minutes this morning. It was about about 80F outside. I drove the car passively and with NO A/C on.... KTMP was 93-99C for about 30-35 minutes.

In the last 10 minutes of the drive, I put the A/C on and as it got hotter outside, about 95F. I accelerated hard to see where the engine temp would go and coolant temp was hovering around 100-102C and jumped up to 105C for a brief second. I was expecting it to be 90-96C but am wondering why it went to 100-105C. That's pretty close to the stock 105C tstat, which is disappointing.... Was it because:

1) The coolant system needs more coolant and because it's a little low, coolant temp isn't as low as it should be?
2) Coolant temp is high simply because it's really hot outside today?
3) Both?

Thoughts?

[Chedley]

To update this thread, I finally got the 88C thermostat from ECS. It took 2 months to arrive!
......
1) The coolant system needs more coolant and because it's a little low, coolant temp isn't as low as it should be?
2) Coolant temp is high simply because it's really hot outside today?
3) Both?

Thoughts?

My thoughts and opinions :
In Physics, the 1st principle of thermo-dynamics states that heat (and energy) cannot be created or destroyed in a closed system. It can only be transferred.
That is, on your car, you can run the engine at a cooler temp, but at the cost of a hotter coolant. You can also run with a lower coolant temp, but at the cost of a hotter engine It is your choice: the stock tstat, or the so-called "coo"l 88c tstat.

My opinion: this cool 88c tstat is a futile experiment. You do not gain anything from it. Forget it.

[DrCharles]

That is, on your car, you can run the engine at a cooler temp, but at the cost of a hotter coolant. You can also run with a lower coolant temp, but at the cost of a hotter engine

Wolfgang Pauli, a famous early 20th century physicist, once said of a colleague's idea, "That's not even wrong".

Whereas you correctly quote a principle of thermodynamics, you are applying it incorrectly. A more useful principle is: Heat always transfers from a hotter source to a colder sink.

You do realize that the t-stat sets the minimum operating temperature of the engine by restricting the coolant flow coming out of it (completely closed at lower temps), so heat builds up quickly in the coolant until it's hot enough to open the t-stat, which opens just enough to balance the flow required with the temperature setting?

The MAXIMUM temp of the engine is not set by the thermostat once it's wide-open. That is a function of the radiator heat-transfer capacity and airflow.

[JimLev]

I agree with you DrCharles.
I’m running the 105ºC t-sat but control it with my own PWM circuit so I can set the temp anywhere between the mid 80ºC all the way up to 108ºC.
I usually keep it in the mid 90ºC’s. The outside temp does have some effect on the engine temp. The KTMP always reads <99ºC even when it’s 100ºF+ outside.
The radiator needs to be clean to get decent airflow thru it, no leaves, pine needles, cig buts, etc.

[ThePhantom!]

Thanks for your input JimLev. Although I am a novice DIYer, I'm very confident I installed the thermostat correctly and bled the cooling system correctly. All parts in my entire cooling system have been replaced correctly in the last two years (15k miles). I researched, read DIYs, watch videos and I took my time with the thermostat replacement. I like to make sure I don't make any mistakes.....

I would like for the KTMP to stay below 99ºC like yours and others on this forum who have installed the lower temp tstat. I may be overthinking it but it bothers me that it jumped up to 100-105ºC today..... The only thing I can guess is that there isn't enough coolant? The coolant was filled to the max in the expansion tank after I bled the cooling system and before I went for a drive. I checked right now after the car has cooled off a bit and it was a little low so I topped it off.

Sorry If i am overthinking things!

edit: the radiator looks free of debris

[JimLev]

I would just keep topping it off in the morning after the engine is COLD.
Don’t overfill it, top of stick just even with the top of the tank or a bit lower is OK.
What’s the temp up in Canada now?

[MotorMouth93]

My thoughts and opinions :
In Physics, the 1st principle of thermo-dynamics states that heat (and energy) cannot be created or destroyed in a closed system. It can only be transferred.
That is, on your car, you can run the engine at a cooler temp, but at the cost of a hotter coolant. You can also run with a lower coolant temp, but at the cost of a hotter engine It is your choice: the stock tstat, or the so-called "coo"l 88c tstat.

My opinion: this cool 88c tstat is a futile experiment. You do not gain anything from it. Forget it.

From this post its pretty apparent that you don't understand the first rule of thermodynamics or how automotive cooling systems work.

The thermostat temperature rating is roughly when the thermostat opens and directs coolant flow into the radiator. In a cooling system with an adequate radiator, for a given driving condition, the thermostat will try to find some equilibrium point somewhere between fully open and fully closed such that the thermostat will maintain a roughly constant temperature around it. When the coolant temp increases, the thermostat opens more allowing more coolant to flow into the radiator, increasing the amount of energy removed from the system, which causes temperature to drop, which cause the thermostat to close, cutting off coolant flow to the radiator and causing system temperature to increase as less heat is being transferred out through the radiator, which causes the thermostat to open again and on and on...

From this, it's clear that causing the thermostat to open at a lower temperature will result in more heat energy being transferred to the atmosphere via the radiator, resulting in an overall lower system temperature, assuming the radiator and fans can handle the increased load. (which the 540i radiator is more than capable of with a decent fan setup)

The benefits of a lower engine temperature are somewhat debatable. Both high and low temperature thermostats have their benefits and drawbacks and its up to you to decide whether a lower operating temp is what you want. Most OEMs run their engines between 85-95C with some being even lower (the S62 has a 79C thermostat and tends to keep KTMP values in the low to mid 80s) so thats why I opted to go with the 88C tstat. The likely reason for the high temp thermostat to begin with was BMW trying to squeeze a few extra mpg out of the M62.

What you gain from an 88C thermostat is less severe heat cycling of plastic and rubber components and lower cooling system pressure.

The 88C thermostat in my car typically holds KTMP between 90-95C even in 100F+ weather. I don't have the stock fan setup though, I remapped my aux fan tables in the DME to come on much sooner, ditched the clutch fan, and have a 16" spal puller attached to the core that kicks on if the aux fan isn't enough which is usually only in stop and go traffic in 105F Texas heat.

[ThePhantom!]

Will definitely top it up.

I'm in Northern California, Sacramento Area. It's over 100ºF for the next few days, 110ºF tomorrow! then high 90s for the rest of the week. It won't be less than 80ºF at any hour of the night for the next 10 days probably...

I am Canadian though! What made you think I was in Canada? haha Definitely don't miss the weather in Toronto where I'm from, the winters are BRUTAL there.

[ThePhantom!]

From this post its pretty apparent that you don't understand the first rule of thermodynamics or how automotive cooling systems work.

The thermostat temperature rating is roughly when the thermostat opens and directs coolant flow into the radiator. In a cooling system with an adequate radiator, for a given driving condition, the thermostat will try to find some equilibrium point somewhere between fully open and fully closed such that the thermostat will maintain a roughly constant temperature around it. When the coolant temp increases, the thermostat opens more allowing more coolant to flow into the radiator, increasing the amount of energy removed from the system, which causes temperature to drop, which cause the thermostat to close, cutting off coolant flow to the radiator and causing system temperature to increase as less heat is being transferred out through the radiator, which causes the thermostat to open again and on and on...

From this, it's clear that causing the thermostat to open at a lower temperature will result in more heat energy being transferred to the atmosphere via the radiator, resulting in an overall lower system temperature, assuming the radiator and fans can handle the increased load. (which the 540i radiator is more than capable of with a decent fan setup)

The benefits of a lower engine temperature are somewhat debatable. Both high and low temperature thermostats have their benefits and drawbacks and its up to you to decide whether a lower operating temp is what you want. Most OEMs run their engines between 85-95C with some being even lower (the S62 has a 79C thermostat and tends to keep KTMP values in the low to mid 80s) so thats why I opted to go with the 88C tstat. The likely reason for the high temp thermostat to begin with was BMW trying to squeeze a few extra mpg out of the M62.

What you gain from an 88C thermostat is less severe heat cycling of plastic and rubber components and lower cooling system pressure.

The 88C thermostat in my car typically holds KTMP between 90-95C even in 100F+ weather. I don't have the stock fan setup though, I remapped my aux fan tables in the DME to come on much sooner, ditched the clutch fan, and have a 16" spal puller attached to the core that kicks on if the aux fan isn't enough which is usually only in stop and go traffic in 105F Texas heat.

Thanks for the clear explanation and benefits listed. Definitely appreciate the info!

[JimLev]

I'm in Northern California, Sacramento Area.
I am Canadian though! What made you think I was in Canada? haha Definitely don't miss the weather in Toronto where I'm from, the winters are BRUTAL there.

Us mods have ways to check things out to limit spam.
Your location said USA so I was wondering where you were located to see if you were in a hot or cold climate.
That post showed Toronto, your last post showed something completely different. Are you using a VPN?

[ThePhantom!]

Ahh that makes sense. I use a VPN to stream free TV shows/Movies available in Canada and left it on!

[ThePhantom!]

I would just keep topping it off in the morning after the engine is COLD.
Don’t overfill it, top of stick just even with the top of the tank or a bit lower is OK.
What’s the temp up in Canada now?

It was 73ºF early this morning. The stick went down a decent bit after cooling overnight, so I topped it off with about a cup of coolant and went for a drive for an hour. In the first 10 minutes of driving, I was seeing KTMP hit a high of 100-102ºC. I then blasted the heater on high for 3-4 minutes, and then turned the air off. KTMP immediately dropped and got down to 90ºF. I left the heat/air off for the rest of the drive (50 minutes). From that point on, whether highway or stop/go, driven lightly or driven hard, KTMP was hitting 93-99ºC the entire time, and mostly between 93-95ºC.

[peter540]

Different versions of the DME firmware will produce different results when removing the thermostat heater circuit. The latest 2003 software won't set a CEL or OBD2 code for the missing heater circuit but will set an internal DME code. But it will set a CEL for P0128/coolant temp too low if you don't properly reprogram the DME for the lower operating temp.

I run the 88° thermostat in my '03 540/6 (manufactured in November 2002). I had the P0128 code until DUDMD helped me program lower temps in the DME. I don't have tools to see whether I'm getting an internal DME code, but the car runs fine. I'm curious to learn what impact would the internal DME code have on operation/performance. Any thoughts?

--P

[MotorMouth93]

The internal code, if present, should not affect performance. It's just there to notify anyone who cares that an issue is detected with the thermostat heater circuit.

[peter540]

The internal code, if present, should not affect performance. It's just there to notify anyone who cares that an issue is detected with the thermostat heater circuit.

Great! Thanks for clarifying...

--P

[ThePhantom!]

I run the 88° thermostat in my '03 540/6 (manufactured in November 2002). I had the P0128 code until DUDMD helped me program lower temps in the DME. I don't have tools to see whether I'm getting an internal DME code, but the car runs fine. I'm curious to learn what impact would the internal DME code have on operation/performance. Any thoughts?

--P

My 540i just threw the P0128 code. The SES light came on in the first 6 or 7 minutes of driving. I used a code reader and found the code.

You mentioned that DUDMD helped you program lower temps in the DME.

What do I need to do to clear the code...or how do I reprogram the DME myself? What tools do I need?

Your help is greatly appreciated.


EDIT: I took a look at another thread and I'd rather not re-program the DME to permanently clear the code incase my tstat goes bad down the line.

For now I've temporarily cleared the code with my code reader/scanner and will continue to do so when the P0128 code intermittently occurs.

[e3954]

My 540i just threw the P0128 code. The SES light came on in the first 6 or 7 minutes of driving. I used a code reader and found the code.

You mentioned that DUDMD helped you program lower temps in the DME.

What do I need to do to clear the code...or how do I reprogram the DME myself? What tools do I need?

Your help is greatly appreciated.


EDIT: I took a look at another thread and I'd rather not re-program the DME to permanently clear the code incase my tstat goes bad down the line.

For now I've temporarily cleared the code with my code reader/scanner and will continue to do so when the P0128 code intermittently occurs.

Are you still running with the code or did you find a fix? I have 03 540i and I'm having the same issue and would like to know if there is a fix since I need smog check. However, I'm getting the thermostat jammed error not sure if that is P0128.

[jicaino]

My car doesn't throw CEL with ot without the resistor. And if I plug in a 12 ohm resistor it will blow it (even a 10W one). and still store the code. But the code is stored when you actually read the DME.

[ThePhantom!]

Are you still running with the code or did you find a fix? I have 03 540i and I'm having the same issue and would like to know if there is a fix since I need smog check. However, I'm getting the thermostat jammed error not sure if that is P0128.

I had to get my car smogged this past week. I couldn’t get around it. If I cleared the p0128 code I cleared the emissions ready data which would fail smog. I tried doing that and then driving using a guide online that gets the car emissions ready within 30 minutes but the code came back.

I ended clearing the code, swapping the tstat from 88c to the stock 105c and then getting the car emissions ready. Finally passed smog.

- - - Updated - - -

[R Shaffner]

The 88C stat hasn't caused a problem for me. No CEL on my '02. Before tossing away my 105C stat, I thought about removing the heater element part and leaving it plugged in, in case it did cause a code. I have no idea whether that's really an option.

[ThePhantom!]

The 88C stat hasn't caused a problem for me. No CEL on my '02. Before tossing away my 105C stat, I thought about removing the heater element part and leaving it plugged in, in case it did cause a code. I have no idea whether that's really an option.

You are lucky. My car shows the p0128 code continuously with the 88c tstat. If I clear it, it comes back. My car is an 03. I hear some cars throw the code. Some don’t.

I also have no clue if what you suggested is an option. I used a 1000 ohm resistor, plugged it in and it didn’t matter, code still gets stored in the DME. Even if it doesn’t show up with the CEL.

[jicaino]

The 88C stat hasn't caused a problem for me. No CEL on my '02. Before tossing away my 105C stat, I thought about removing the heater element part and leaving it plugged in, in case it did cause a code. I have no idea whether that's really an option.

Nope, it's gooped in. What you can do is remove the 105°C element from the housing and replace it with the 88°C element. I had a video showing how to, but I don't know where it went.

[Dking078]

Later versions of the M62TU software scan/report the thermostat code. That's why some 2002 and earlier have no issues.

[jicaino]

Later versions of the M62TU software scan/report the thermostat code. That's why some 2002 and earlier have no issues.

I think it's later versions of the actual DME hardware's SW. I have the last update on my part number DME and it's from '05-06 if I remember correctly, and it doesn't reports squat. Then again, my car's euro, and 8/99.