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Thread: 88c thermostat characteristics

  1. #1
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    88c thermostat characteristics

    Im looking for some 88c tstat data. I have a friend who installed this in his 03 e39 540 with auto trans and it would run between 90 and 97 between idle and driving speeds which is shown with the unlocked cluster. Then later on the same day and days after he started noticing it is now getting up to 108 which is normal operating temperature with the stock 105c tstat with the electronic plug for the heating element. Im looking to instsll this on my 2000 e38 auto with the m62tu as well but don't want to even attempt it if the temps will still get up to 105-108 which it is using the stock tstat. Im thinking he may have no bled the cooling sysyem correctly or the tstat is bad put of the box? So the question is what are you guys with the 88c tstat seeing for operating temperature? I tun my cluster unlocked to test 7 literally ways because its good to have the coolant temp info to look at while driving. I've read people saying it typically runs 90-93c but im looking for a broader view of the temps people are seeing during all driving conditions and if it actually hold the temps at below 95c or does the temp rise to over 100c and drop back down and do alot of fluctuating up and down? Any feedback would be greatly appreciate and im posting here because this mod seems to be more popular with the 540s...

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    Last edited by purplecty; 08-13-2018 at 06:10 PM.

  2. #2
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    I drive a lowly 528 but I have an 88 degree thermostat and have monitored my coolant temps with test 7 for a few years now. During the colder winter months the temps normally fluctuate between 87-90, and during the hot summer months it goes from 87-94. I don't remember it ever exceeding 94, and that includes stop and go traffic with the air conditioner running and 95 degree ambient air temps.
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  3. #3
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    Sorry for not using Celsius. I see 189-194° F with the 88° C thermostat on my boosted M62tu. I am also running a CSF radiator and all AC components have been removed.

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    Last edited by setho; 08-13-2018 at 03:26 PM.

  4. #4
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    I am running around 102C in a stop and go traffic, I also have electric fan conversion too.

  5. #5
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    Quote Originally Posted by theWalkinator View Post
    I am running around 102C in a stop and go traffic, I also have electric fan conversion too.
    Isnt that considered on the high end for an 88c tstat conversion?

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  6. #6
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    Quote Originally Posted by purplecty View Post
    Isnt that considered on the high end for an 88c tstat conversion?
    Well, I also have AC on but I am happy with it, before the car in the same situation can heat up to 118C and mechanical fan robbed a lot of power, making the car felt very sluggish. I saw someone in this forum runs lower than mine with 88C tstat mod, maybe I need re-bleed the cooling system?

  7. #7
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    Quote Originally Posted by theWalkinator View Post
    Well, I also have AC on but I am happy with it, before the car in the same situation can heat up to 118C and mechanical fan robbed a lot of power, making the car felt very sluggish. I saw someone in this forum runs lower than mine with 88C tstat mod, maybe I need re-bleed the cooling system?
    118c on regular oem tstat is no good. It shouldn't exceed 110c...

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  8. #8
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    Mine runs a consistent 92-97. Pressure in the cooling system is around 5-7 psi. At 110C it was up around 13-15 psi if I remember right.
    Recently removed my mechanical fag after my electric fan started working again. It didn't work until I bought a new one, than it started working. Must of felt threatened.

  9. #9
    geargrinder's Avatar
    geargrinder is offline Having No Trouble Here BMW CCA Member
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    I'd rather shoot myself in the Magic Johnson with a BB gun than have to do the cluster button dance each and every time I get in the car to watch KTMP. Man that must be annoying. That's what I have the needley-pointy-thing on the right side of the cluster for. :P

    Purpleocity: have you considered your dual-temp sender might be mis-calibrated? I'd agree that your reports sound a little high. Maybe one or the other half of your temp sensor is drifting... that seems to be what they do - drift up in value before they totally crap out...
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  10. #10
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    Quote Originally Posted by geargrinder View Post
    I'd rather shoot myself in the Magic Johnson with a BB gun than have to do the cluster button dance each and every time I get in the car to watch KTMP. Man that must be annoying. That's what I have the needley-pointy-thing on the right side of the cluster for.

    Purpleocity: have you considered your dual-temp sender might be mis-calibrated? I'd agree that your reports sound a little high. Maybe one or the other half of your temp sensor is drifting... that seems to be what they do - drift up in value before they totally crap out...
    Im all about that digital precision with my KTMPS! It's almost as easy to unlock the cluster KTMP than starting the car and is better than any of the other garbage on the cluster display... The dual temp sensor you mention is the one on the water pump?

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    Last edited by purplecty; 06-01-2020 at 11:56 PM.

  11. #11
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    Yep. Easy replacement. Coolant barely even drips out if you swap it fast and leave the cap on (vac lock type of deal).

    You can measure the values of both sides of it and compare, if they aren't nearly exact the same then one side is losing its poo.

    - - - Updated - - -

    BTW - agree about the pointlessness of the display otherwise... I'm not using my BC 'stopwatch' features all that often... if I could get temp and or volts etc. to be in the 'scroll' for the BC display, then THAT would be excellent.... would be great if a bunch of stuff like that was easily clickable. Somebody re-write the BC/cluster firmware please.
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  12. #12
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    Iirc both sides of new dual temp sender don't match resistance. But I got crs sometimes so...
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  13. #13
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    Quote Originally Posted by philly98540 View Post
    Iirc both sides of new dual temp sender don't match resistance. But I got crs sometimes so...
    What are your 88c tstat characteristics while driving? I know you were one of the first to do this mod?

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  14. #14
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    I have a pre TU motor with an 85 degree stat (no 88C avialable for pre TU) and Evans coolant, so not apples to apples with what you have, but similar in any event. During 95% of my driving I see KTEMPs in low 90's. During 95F+ heat wave humid AF with AC on full blast, I see 102C KTEMP's here and there. KTEMP is measured after coolant is heated by the engine, while the TSTAT controls input to the engine if I understand the flow circuit correctly, so the KTEMP should track above the TSTAT a bit. My Evans coolant has less specific heat than 50/50 normal coolant, so it heats up a little more as it travels through the block and heads. To get better hot weather control on my set up, I need to upgrade to a thicker core radiator (like M5 version), but I'm happy where it sits now.
    98 540i 6, 525 whp, 120 mph 1/4, V3 Si S/C'er @16 psi, W/A I/C, Water/Meth, Supersprint Headers, HJS Cats, 3" Custom Exhaust, UUC Twin Disc, Wavetrac LSD, GC Coil Overs, Monoball TA, AEM FP, Aeromotive FPR, AEM Failsafe AFR/Boost, Style 65's w/275's, M5 Steering Box, Eibach Sways, M3 Shifter, Evans Coolant, 85 Deg Stat, PWM Fan, 10" Subs, B.A. speakers, Grom Aux/BT, Still Rolling as my DD!

  15. #15
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    The KTMP will show both sides of the dual temp sensor.

    Key in position two (engine running position) will give one temp.

    Click back to position one, and it will show the other temp. Should be within a degree or two. A faulty connection on one side will show -40C or some other weird number.

  16. #16
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    Good call I always forget that trick.
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  17. #17
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    Just to update this thread, I have been running the 88c tstat in my e38 for a while now and it has been running 91-93c consistently...

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