Thermostat

[bmw540san]

It's well established by know that the map controled thermostat is great in theory and improves fuel economy but at the cost of increasing pressure on cooling system (more heat = more pressure).

Also, if component in cooling system fails (and it will), you're much closer to potential serious problem of overheating vs running on cooler thermostat.

I've ran this on my E53 4.6is and have sold few dozen to E39 forum members couple years ago. I've had good connection in Europe and got this for much better price. This is OEM thermostat for E38 740D never sold in US.
https://www.ecstuning.com/b-genuine-...CABEgKFZ_D_BwE

Direct fit other than installing simple resistor into disconnected wiring connector to avoid CEL.

[oldskewel]

Originally Posted by bmw540san

It's well established by know that the map controled thermostat is great in theory and improves fuel economy but at the cost of increasing pressure on cooling system (more heat = more pressure).

Also, if component in cooling system fails (and it will), you're much closer to potential serious problem of overheating vs running on cooler thermostat.

I've ran this on my E53 4.6is and have sold few dozen to E39 forum members couple years ago. I've had good connection in Europe and got this for much better price. This is OEM thermostat for E38 740D never sold in US.
https://www.ecstuning.com/b-genuine-...CABEgKFZ_D_BwE

Direct fit other than installing simple resistor into disconnected wiring connector to avoid CEL.

I've been hoping for something like this to be available. So did you install that on your E53 M54?

Did you install a resistor? I expect based on my measurement mentioned above, that a 15 Ohm, 15 Watt [or higher] load resistor would be needed to sufficiently convince the ECU that all is good.

I found this youtube video that shows it. One of the comments says that they did nothing with the resistor and no CEL ever came on. If that is true, I'll guess they still had that code I mentioned above - I got no CEL, but did have that DME code that my Foxwell read. I'd be at least a little concerned that the ECU does not do something in response to that.

https://www.youtube.com/watch?v=PfyYw6LkHiE

Otherwise, I'll probably get one of these ... as soon as I fix my engine.

[bmw540san]

Originally Posted by oldskewel

I've been hoping for something like this to be available. So did you install that on your E53 M54?

Did you install a resistor? I expect based on my measurement mentioned above, that a 15 Ohm, 15 Watt [or higher] load resistor would be needed to sufficiently convince the ECU that all is good.

I found this youtube video that shows it. One of the comments says that they did nothing with the resistor and no CEL ever came on. If that is true, I'll guess they still had that code I mentioned above - I got no CEL, but did have that DME code that my Foxwell read. I'd be at least a little concerned that the ECU does not do something in response to that.

https://www.youtube.com/watch?v=PfyYw6LkHiE

Otherwise, I'll probably get one of these ... as soon as I fix my engine.

I've only done it on M62/TU V8 and I'm not aware there is similar option for M54.
I personaly would not do it on M54 because its thermostat is 92 C IIRC which is quite "normal" temp. vs 105 C on M62.

[Clavurion]

Originally Posted by bmw540san

I've only done it on M62/TU V8 and I'm not aware there is similar option for M54.
I personaly would not do it on M54 because its thermostat is 92 C IIRC which is quite "normal" temp. vs 105 C on M62.

AFAIK M54 engine has exactly same cooling logic and temps as M62. (Same kind of map controlled thermostat already on M52TU engine.)

[carbob]

I may need a bit of clarification about the big picture here. Is the balance the MAP thermostat is trying to achieve between higher temps that lead to better gas mileage and lower temps that lead to better emissions? That seems to make the most sense to me, having a hotter thermostat for overall good mileage but adding the DME managed control based on emission sensed feedback to improve emissions at times of poor emissions like high RPM’s by dissipating the heat. So I’ve read that failure of the thermostat means it is open as a fail safe, and I wonder if the failure of the MAP control also fails in the open position? The logical result would be a cooler engine than would otherwise happen with a good thermostat, which means better emissions, worse gas mileage, and maybe faster heater operation. Interestingly my mileage has been creeping lower, now about 15.3 overall on the dash computer, my temp gauge starts moving quickly after start and a very fast heater output on startup. I used to have mileage in the 16mpg range.

[bmw540san]

Originally Posted by carbob

I may need a bit of clarification about the big picture here. Is the balance the MAP thermostat is trying to achieve between higher temps that lead to better gas mileage and lower temps that lead to better emissions? That seems to make the most sense to me, having a hotter thermostat for overall good mileage but adding the DME managed control based on emission sensed feedback to improve emissions at times of poor emissions like high RPM’s by dissipating the heat. So I’ve read that failure of the thermostat means it is open as a fail safe, and I wonder if the failure of the MAP control also fails in the open position? The logical result would be a cooler engine than would otherwise happen with a good thermostat, which means better emissions, worse gas mileage, and maybe faster heater operation. Interestingly my mileage has been creeping lower, now about 15.3 overall on the dash computer, my temp gauge starts moving quickly after start and a very fast heater output on startup. I used to have mileage in the 16mpg range.

Here is a good expanation, straight from BMW manual:
https://www.meeknet.co.uk/E38/E38_Map_Thermostat.pdf

That is all great in theory but I still prefer 88 C conventional thermostat "upgrade" which is safer overall for cooling system components (less heat = less pressure) while it still produces temps hot enough for long term engine health.

I know from experience that mpg difference is pretty much non exsistant, at least I haven't noticed one on my X5 4.6is with M62TU.

[bmw540san]

Originally Posted by Clavurion

AFAIK M54 engine has exactly same cooling logic and temps as M62. (Same kind of map controlled thermostat already on M52TU engine.)

Yes, it has the same cooling logic but the big difference is the actual mechanical wax controled opening temp which is around 13 C lower (92 C vs 105 C) which is a huge difference when the cooling temp is hovering around 100 C.

[Clavurion]

Originally Posted by bmw540san

Yes, it has the same cooling logic but the big difference is the actual mechanical wax controled opening temp which is around 13 C lower (92 C vs 105 C) which is a huge difference when the cooling temp is hovering around 100 C.

Where are you getting this information?

[carbob]

Thanks for all the input, but I may have misinterpreted some of the information I have been reading, and I don’t want anyone reading this to get the wrong impression, so I’ll try to correct myself here, please let me know if I still don’t have it right. Higher engine temps and cooler, dense air provide for better combustion, better mileage and better emissions. So BMW engineers added a higher set point thermostat, but recognized that higher temp means more risk of engine damage, that is the balance they are trying to achieve. The information shows that thermostat opens at engine outlet temp of 110C without DME control information. But the added functionality of the MAP allows the thermostat to open at lower temps if there is a need for better combustion- as in high RPM’s; and it fully opens the thermostat at 113C outlet temp regardless of any other parameters. So the engine is allowed to run a little hotter but mitigated from running too hot. This is a good thing overall, but adds some complexity and maintenance- they always seem to go hand in hand. I hope that helps.

I did replace the water cooled thermostat……but immediately on starting the engine the battery icon stayed lit on the dash. With the engine running there is 11.8v which looks like no charging and a new alternator is needed. If interested see new thread “Another Alternator”.