Lowering Coolant Temp

MDORPHN

Corporal
Jan 28, 2018
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BMW 1M
Even if you flash the DME to run the pump faster -- as I can do with MHD, am I correct that the lower limit will be the temp at which the thermostat opens (which I believe is 97 C/207 F)?

Or is the stock thermostat itself electronically controlled so that the flash tune can set it to open at a lower temp?

Thanks.

EDIT: Just found a post from my old friend JamesM3M5 that answers my question:

"The ECU will regulate both the thermostat opening and water pump speed to maintain the proper temp. The two wires going to the thermostat are for a tiny heater that will heat up the wax plug and open the thermostat earlier than its advertised temperature."

Neil
 
Last edited:

veer90

Captain
Nov 16, 2016
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West Nyack, NY
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e90 335i 6MT
Not sure how it all works but it's definitely doable. I can have coolant sitting at 180-190 all day normal driving with the coolant target set to track. Then again I have a CSF rad.

ymmv with the stock rad.
 

RSL

Lieutenant
Aug 11, 2017
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Target temps for modes are cylinder head temps, not coolant. ECT can and will run much cooler as needed. I'm able to hit high mode on factory settings during summer in TX, ECT will run 165-170F and OCT hangs around during 195-210F usually. 335is with the extra rad and 800w fan, so a bit more capacity for heat exchange.
 

The Convert

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Jun 4, 2017
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Target temps for modes are cylinder head temps, not coolant. ECT can and will run much cooler as needed. I'm able to hit high mode on factory settings during summer in TX, ECT will run 165-170F and OCT hangs around during 195-210F usually. 335is with the extra rad and 800w fan, so a bit more capacity for heat exchange.
What all is required to retrofit the is fan, do you know?
 

RSL

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Aug 11, 2017
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There's a discrete relay for it, but if any coding changes or other connections are needed to control it, I'm not sure.
 

MDORPHN

Corporal
Jan 28, 2018
196
158
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Ride
BMW 1M
I'm already running a Mishimoto radiator and my 1M has the additional heat radiator and 800W fan.

I also am running a MHD tune (thank you MOTIV) so run the pump on track mode.

However, my question is regarding operation of the thermostat, which I believe is a "traditional" mechanical piece that I'm told opens at 97C/207F. If this is the case (and I'm not sure it is), how would it be possible for a flash tune to produce coolant temps below those values?

BTW, Mishimoto does sell a 165F "racing thermostat" but I haven't found any one who has successfully installed it.

Neil
 

RSL

Lieutenant
Aug 11, 2017
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I'm already running a Mishimoto radiator and my 1M has the additional heat radiator and 800W fan.

I also am running a MHD tune (thank you MOTIV) so run the pump on track mode.

However, my question is regarding operation of the thermostat, which I believe is a "traditional" mechanical piece that I'm told opens at 97C/207F. If this is the case (and I'm not sure it is), how would it be possible for a flash tune to produce coolant temps below those values?

BTW, Mishimoto does sell a 165F "racing thermostat" but I haven't found any one who has successfully installed it.

Neil
I haven't had one apart, so I can't say with 100% certainty, but you've kinda answered the question: if it were a simple mechanical piece, a flash wouldn't be able to change the operating parameters. Even the thermostat on my E46 had the DME's finger managing it. It used heating elements inside to control it (that one I did take apart).

High+KFP = high cooling mode + mapped thermostat and is the only mode that indicates it actively manages the thermostat. Other modes may rely on a mechanically managed (but monitored) opening, I can't say for sure. The DME is always going to attempt to run the temps high no matter what you do though, unless you the tell DME to do otherwise. In other words, any mode other than High+KFP may attempt to slow the water pump/fan to offset a cooler thermostat. Again, not 100% sure, just an educated theory. I know for a fact that my temps are relatively stable regardless of mode until High+KFP goes active, then they go almost too cold.

Stock High+KFP table should be targeting 175F ECT whenever it's over 68F ambient and mine will actually run down into the 160s with that on a totally stock 335is cooling system and 85k mile water pump/thermostat.
 

AZN54

Private
Nov 18, 2016
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Mesa, AZ
Good info here, thanks guys. Have you heard of any correlation between the MHD coolant temp flash versus premature pump failure? I personally haven't seen much on this, but Im assuming driving the pump harder/longer may reduce its lifespan.
 

RSL

Lieutenant
Aug 11, 2017
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I've not heard any, but certainly, the harder/more often you use things, the quicker they wear out. Just note that the modes are BMW's, MHD flash options just change the triggers and targets so it doesn't have to be 90-97F+ ambients to get the extra cooling.

I'm on High+KFP almost daily for 2-4 months a year for 4.5 years and have 85k miles on the original water pump.
 
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VACust

Corporal
Dec 1, 2016
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US - Utah
I'm already running a Mishimoto radiator and my 1M has the additional heat radiator and 800W fan.

I also am running a MHD tune (thank you MOTIV) so run the pump on track mode.

However, my question is regarding operation of the thermostat, which I believe is a "traditional" mechanical piece that I'm told opens at 97C/207F. If this is the case (and I'm not sure it is), how would it be possible for a flash tune to produce coolant temps below those values?

BTW, Mishimoto does sell a 165F "racing thermostat" but I haven't found any one who has successfully installed it.

Neil
Early N54s have a different thermostat housing and that is the one Mishimoto made the low temp T-Stat for. Not many cars have it, just a few early 2007. The newer housings don’t come apart the same way so the Mishimoto T-Stat doesn’t work in them.
 

The Convert

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Jun 4, 2017
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Early N54s have a different thermostat housing and that is the one Mishimoto made the low temp T-Stat for. Not many cars have it, just a few early 2007. The newer housings don’t come apart the same way so the Mishimoto T-Stat doesn’t work in them.
Have any pics? I have an 06-06 build 335.