99-03 540i drivers what is your Coolant KTMP Low-High range when driving?

[AngelEye5]

Its on OBC test #7, so far my temps when driving are-
108-110C or 226.4-230F High
105C or 221F Low

Is this normal? When its just being idle it will drop to a Low of 93c or 199.4F due to the electrical 12V feed into the heating element inside the thermostat.

The vehicle service history shows the water pump was changed at 60k and the thermostat was changed at 50k now at 123k.

[gmak]

Yes. That is perfect for a 540i (the operating temperature). I'm not sure about the low - but I suspect that it is fine since the thermostat is DME controlled and why run hot when you're idling? If your thermostat was stuck open, it would never read 105C.

The thermostat is 105c meaning that it will open at that temp mechanically if something goes wrong. The DME can open it much sooner with an electric signal that melts the wax in the thermostat and this opens the device.

[philly98540]

Your driving Temps are good. You idle is low for some reason. Maybe stat not seating fully. Not sure.

The stat uses the standard mechanical portion for 99% of normal driving. The electric heater part only kicks in to lower the temp during extended full throttle abuse and if Temps go way high. There is a nice bmw tutorial on its operation if someone has the link.

[Mach540]

Your temps are pretty much what I was getting.... Till yesterday
I installed an 88C thermo and now it stays right at 93-95C.
For some reason, I'm not getting an error message for the missing electrical connection either. I did buy a resistor to use as a simulator, but so far I don't need it.

There is a nice bmw tutorial on its operation if someone has the link.

I'd like to see that.

[jicaino]

Mine operates like that. (City driving, right?) It will stay between 103/108°C and occasionally drop to 92°C when MAP cooling is active.

[Mach540]

Mine operates like that. (City driving, right?) It will stay between 103/108°C and occasionally drop to 92°C when MAP cooling is active.

It does????

I thought yours didn't operate AT ALL!!

[jicaino]

It does????

I thought yours didn't operate AT ALL!!

It's currently hurt, but she'll rise again. On that engine or on another. NMW.

[charliejones408]

Your temps are pretty much what I was getting.... Till yesterday
I installed an 88C thermo and now it stays right at 93-95C.
For some reason, I'm not getting an error message for the missing electrical connection either. I did buy a resistor to use as a simulator, but so far I don't need it.


I'd like to see that.

Hi, I have been averaging around 108 c. in my 1997 540i Sport. Your readings are more for the inline 6 so wanted to ask running this cool was there a lack in performance and did it affect mpg. I don't like running my engines this hot so if you didn't experience any negative issues i'm thinking about doing the same thing!! Thanks Charlie

[jicaino]

Update to an old thread, I swiotched over to the 88ºC thermostat and never had a problem again. Operates between 87ºC and 92ºC open road steady speed, and 90ºc to 94ºC around town, heavy traffic, aircon on, and summer/winter it's the same.

[RuskiE39]

A stock and normal operating thermostat on the 540i shouldn't exceed 110C. Mine occasionally fluctuates between 98-110. 110 in stop and go traffic when the temperature is warm - seldomly hitting 111.

[charliejones408]

Update to an old thread, I swiotched over to the 88ºC thermostat and never had a problem again. Operates between 87ºC and 92ºC open road steady speed, and 90ºc to 94ºC around town, heavy traffic, aircon on, and summer/winter it's the same.

I have decided to switch over to your suggestion using a 88 degree C thermostat. I'm having a hard time finding one. Where did you get your Thermostat? Thanks Charlie

[jicaino]

I have decided to switch over to your suggestion using a 88 degree C thermostat. I'm having a hard time finding one. Where did you get your Thermostat? Thanks Charlie

Hey! Got mine from a forum member who imported them from Germany. I then got 4 extra units for folks down here... I think I have 2 left somewhere and I could be selling the 540i so maybe I can fix you with one. I'll have a clearer picture in about 8/10 days

[Texasdeere]

With the stock thermostat mine used to run around +/- 226 F

Now with the 85 C thermostat it runs around 194 to 196 F

[JimLev]

I'm using the stock 105ºC t-stat but made a PWM circuit so I can set it from 80ºC all the way back up to the stock 108ºC KTMP.
I usually have it set so the KTMP is 94-95ºC.
I like keeping the coolant system pressure lower than the stock 16+ PSI.

[scottieducati]

with 88C tstat I’m seeing 90-93C


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[Santaclaus4]

I could be selling the 540i

Nooooooo….

[jicaino]

I'm using the stock 105ºC t-stat but made a PWM circuit so I can set it from 80ºC all the way back up to the stock 108ºC KTMP.
I usually have it set so the KTMP is 94-95ºC.
I like keeping the coolant system pressure lower than the stock 16+ PSI.

This is just like using a 88ºC de facto

[jicaino]

Nooooooo….

Manual swap isn't going to happen and even so, I still hate the glass sunroof (Easy swap) and the BMTV/IKE high which would require to tear down the entire interior. Might as well part ways with her with a tear in our eyes, instead of gutting her and half away completion realizing I don't live in a country were I can source salvage parts that easy and ending up selling for parts or chopping her to pieces myself.

[JimLev]

This is just like using a 88ºC de facto

True, just costs less and no need to bleed the cooling system.

[jicaino]

True, just costs less and no need to bleed the cooling system.

I bleed and replace the coolamt at least once a year so it wasn't that big of a deal.

[scottieducati]

I should note that at least for now I’m running without the clutch fan. GG did tweak the aux fan operation so it kicks on around 91C for me atm.


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[JimLev]

I bleed and replace the coolamt at least once a year so it wasn't that big of a deal.

Wow, that's overkill. I do mine about every 4 years, but that is usually only 10K miles.

[jicaino]

Wow, that's overkill. I do mine about every 4 years, but that is usually only 10K miles.

4 years!!!!! Can you hear my OCD cringing?

[Mike WW]

4 years!!!!! Can you hear my OCD cringing?

It's the 10K miles in 4 years that have me shaking my head. That's about 8 or 9 months for me since it's no longer the vacation car. Used to be more miles.

[JimLev]

4 years!!!!! Can you hear my OCD cringing?

Got 3 cars, my wife likes the Highlander much better than my 540.
She's going to hate the '33 hotrod.
OK, so I figured wrong, it's been 9K miles in 3 years, 3K a year.