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Discussion Starter · #1 ·
Hey guys and gals,

The YouTube channel "B is for Build" is currently patching together a 2001 e46 325i for Oregon's "500/500 Rally", where one takes a $500 car and drives it for 500 miles on fire roads and whatnot.

Anyways, Chris of B is for Build has built a custom cooling system, but he'd like to lower the operating temperature of the thermostat to reduce the chance of it exploding catastrophically, as they are using a junkyard radiator.

So far, I know you can reduce the coolant temperature a few different ways. You can do it by tuning the car, which will tell the engine computer to heat the wax element more aggressively. You can do it through a thermostat plate kit, like that from Zionsville Autosport. You can drill holes in the thermostat, like this. Or you can order a Mishimoto racing thermostat.

But I'm wondering if there is a mechanical modification - outside drilling holes because that would drastically increase warm up time - one can make to reduce the coolant temperature of the M54 thermostat. Some modification to the spring or shaft or something similar that would simply reduce the temperature would be much appreciated.

A few notes:
It has to be free, or extremely low-cost.
It has to be done soon, preferably doable in less than an hour, including thermostat removal time (which should be a piece of cake, looking at the car), less than 3 days from now (so part-shipping is out of the question).
Engine codes are irrelevant.
Coding is out of the question unless someone from Portland is willing to do the coding in the next few days for free.

Any help is appreciated.

Nate
 

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If pressure is your concern, why not attack that directly. Change out the pressure relief cap on the reservoir for a lower pressure one.
 

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Just apply 12 Volts to the thermostat connector for the heater in the thermostat.

As long as the thermostat heater is no burned out, this will drop the engine temperate by around 20F as I recall??

You could also set up a toggle switch to control the stat heater from the drivers seat.

I think?? one side of the connector may have +12 Volts all the time or has +12 when the ignition is on and the DME usually controls the ground side to turn or activate things.

So you may be able to cut just a single wire and either ground it on the stat side or add a ground switch.

I might need to look at the wiring diagram to be 100% how the stat is controlled, I am basing my above comment on how most other devices are controlled by the DME.
 

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Discussion Starter · #5 ·
Thanks for the quick replies!

If pressure is your concern, why not attack that directly. Change out the pressure relief cap on the reservoir for a lower pressure one.
Something like the GermanAutoSolutions.com cap? I'll pass that along; not sure the budget will allow.

Why not just drill a 1/2" hole in the thermostat.

any sort of lemon chump $500 race car build I had, that would probably be my answer. They are can be very restrictive, you don't want to spend money modifying the cars lol.
At that point, what adverse affects would running without the thermostat entirely cause?

Just apply 12 Volts to the thermostat connector for the heater in the thermostat.

As long as the thermostat heater is no burned out, this will drop the engine temperate by around 20F as I recall??

You could also set up a toggle switch to control the stat heater from the drivers seat.

I think?? one side of the connector may have +12 Volts all the time or has +12 when the ignition is on and the DME usually controls the ground side to turn or activate things.

So you may be able to cut just a single wire and either ground it on the stat side or add a ground switch.

I might need to look at the wiring diagram to be 100% how the stat is controlled, I am basing my above comment on how most other devices are controlled by the DME.
Hmm, I like this one. Can I use the WDS on BMW-planet to figure this out? Be back in a sec...
 

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Discussion Starter · #7 ·
Screen Shot 2016-04-26 at 11.24.50.png

So looking at this screenshot of the MS43 Map controlled thermostat, if I ground the gray-brown wire, I should have a thermostat that is constantly open... right? Or do I have that backwards...
 

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Discussion Starter · #11 ·
Unfortunately we don't have time or money for that; $500 budget build. Does anyone know if I just ground the gray/brown wire on the thermostat if it should run open the map-controlled part of it?
 

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View attachment 630473

So looking at this screenshot of the MS43 Map controlled thermostat, if I ground the gray-brown wire, I should have a thermostat that is constantly open... right? Or do I have that backwards...
Kind of right.

If you cut the Gray/Brown wire and ground it or tie it to a toggle switch, it opens the thermostat a bit early and will drop the operating temp around 20F as I recall.

It is not constantly open, it just pre-warms the wax pelllet and causes the stat to open early, dropping the baseline engine temperature.

You might be able to do something similar by spoofing the oil temp high. I this enabled the stat heater and may run the cooling fan at a higher speed?

There is also a heater core temp sensor behind the radiator that you can also do this with.

The problem with spoofing the temps, it may cause the timing and VANOS to retard a bit an loose power. Not 100% sure about this, however, there are some fail safe features built into the car.
 

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Discussion Starter · #13 ·
Based on info I've seen elsewhere, it looks like the coolant temperature is controlled in 3 phases. The first is when the engine is cold, below approximately 80ºC. That seems to be mechanically controlled, somehow. I've never seen my car below 80ºC, even with super aggressive driving, except for at cold start. Next phase is computer controlled, which uses the wax to open the thermostat around 97ºC in normal operating conditions. Finally, according to Zionsville Autosport, a mechanical failsafe is built in around 110ºC, though I've never seen evidence of that.
 

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Do not over think things.

The thermostat is a simple mechanical thermostat that keeps the engine temperature at a "nominal" 96C. The only difference is the heater element that "spoofs" the the thermostat to open earlier. It makes the stat think the engine is at 96C when it is actually running around 85C. If the heater was constantly on, the stat would just open earlier, might actually take bit longer to warm up??

The computer can turn the heater element on in the thermostat, it heats the wax pellet and causes the thermostat to effectively become no different than a mechanical thermostat of a lower operating temperature.
 

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The only part I do not fully understand is if the DME actually "modulates" or controls the power to the thermostat heater element to keep the engine temp from dropping too low or if there is a mechanical limitation that will keep the engine temperature at just a lower value.

I believe, based on some prior cases, that the temp will just be reduced by a fixed value after working with some members here on the forum with problems that caused the thermostat heater to be commanded on full time and the engine to ran consistently cold.

This is why a toggle switch in the cabin may be useful?

But I am sure you can test out the feature and report back how things work out.
 

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The only part I do not fully understand is if the DME actually "modulates" or controls the power to the thermostat heater element to keep the engine temp from dropping too low or if there is a mechanical limitation that will keep the engine temperature at just a lower value.

I believe, based on some prior cases, that the temp will just be reduced by a fixed value after working with some members here on the forum with problems that caused the thermostat heater to be commanded on full time and the engine to ran consistently cold.

This is why a toggle switch in the cabin may be useful?

But I am sure you can test out the feature and report back how things work out.
Quote from a bmw tech I asked a few years ago; the DME's role is to prematurely open the thermostat under certain engine load. Tempoeratre feedback from the sensor under cylinder #6 is taken where the coolant is most far away from thermostat and will likely overheat before reaching and thus mechanically opening the thermostat. The modulation is to prevent overheating, not to prevent overcooling.
 
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