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Thread: Thermostat control M157/M278

  1. #1
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    Thermostat control M157/M278

    I don't suppose anyone has figured out how to control the little heater in the thermostat for M157 & M278?
    I ask because my stat died and the new stat is holding temps 10-15F higher on avg than the old one, and buggin me bad. Not sure if the little heater is already giving it 100% or not, but would be nice to adj it either way.

    I looked for a colder aftermarket stat but found nothing. From what I can tell oem is 217F, and with the heater unplugged it hovers ~216-217F, so that seems ok. Then the heater adjusts temp down from there. I can only assume the new one is stiffer? Meaning the same heater input doesn't open it as much? I dunno.

    I'm using the original heater element btw, because the one that came with the stat didn't make sht for heat, basically almost identical to unplugged.
    '16 E550 Coupe RWD - C207.373 / M278.922 / MED17.7.3 / 722.909

  2. #2
    Advanced Tuner outlaw_50's Avatar
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    The thermostat on M157/M278 is mechanical not like the M177 electrical which you could control it through tune.

    The only option you got is Blackboost Thermostat (always fully open)
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  3. #3
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    It's electric. Or I should say mechanical with electric boost. Without the electric heater the water temp hovers around 217F, which I read online is the oem mechanical rating. With the heater it can force it to open at a lower temp, which it always does, but not as low as the old stat did.

    Before I replaced the stat it usually stayed ~180F +-5 at this time of year, as long as I was moving of course. This new stat is hovering ~200F. Since I started this thread I noticed the new one will open when I floor it, but it takes too long. So if at 200F and I gas it, it will drop to ~165-170, but it take 90 seconds to get there. Not sure about you but 12 seconds is the longest I've floored it, so it's pointless. Once it hits that 165-170 it'll go right back up to 200, which takes another 90 sec.
    So the ECU can open the stat when it wants to, and that setting is in there somewhere...

    The Blackboost dealie would be too cold, and take too long to warm up, otherwise I would.

    Stat assy heater.jpg
    '16 E550 Coupe RWD - C207.373 / M278.922 / MED17.7.3 / 722.909

  4. #4
    Senior Tuner Norris Motorsports's Avatar
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    Black Boost should state their thermostats require ECU tuning before stock cars, looking for better coolant temps, install the kit.

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  5. #5
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    I'm curious why it would require tuning? Or are you referring to the CEL it will generate?

    As mentioned, the BB dealie would take too long to warm up. I need my heater/defrost to work. Even with the stat it takes a long time to warm up.

    Maybe nobody knows where the stat heater code is to adjust it? If not, I rekon I will have to apply power directly to it.
    '16 E550 Coupe RWD - C207.373 / M278.922 / MED17.7.3 / 722.909

  6. #6
    Senior Tuner Norris Motorsports's Avatar
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    Yes for the CEL codes generated.

    Norris Motorsports
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