PSA: M62's BE CAREFUL of 88C T-stats & BMW code 0x8B / 139 (PeePee code P0128)

[geargrinder]

Cut to chase:

If you have retrofit an 88C T-stat, DON'T drive around with the SES on and error code 139, as it may disable your AUX fan.

Seems like later cars fitted w/ the 88C non-MAP thermostat, even with a resistor fitted, will generate a error code 139 for a 't-stat stuck' because the temp is too low. Although we had noticed that before, nobody had noted any significant problem with this.

Well today, rush hour traffic, hot and sunny, coming home from ScottieDucati's, my car overheated very solidly in 90's temps in creeping traffic w/ AC on. Pulled over and noted AUX fan was not operating at all. FORK ME I think, AUX fan has died, JimLev can laugh his azz off in NewMex and I have to chug a big cup of his IFTYS. CRAP, now Jim will bust my nuts for for now until the end of forever.

Hook up the computer to check codes and see if anything shows up, and, well, yeah.... I had gotten lazy about resetting the t-stat code, so the SES light had been on for a couple days as I thought "OK harmless t-stat error". I knew that was there, didn't think much of it. So while letting car cool down, I cleared the code (thank Jebuz for having the computer w/ me) and instantly the AUX fan is howling away, doing its job perfectly.

Now VERY obviously in hindsight the DME logic is if the T-stat is failing 'low' then it will never activate the fan so as to not run the engine w/ too low operating temps.

In retrospect I had kinda noted the other day "huh I'm surprised I don't hear the AUX fan running" after I parked it on a fairly hot day. Dumbass. Shoulda looked a bit into that I guess.

And I"m not 100% off the hook for nut busting, as of course if I had any kind of 2nd fan, I'd have been driving around blissfully unaware of the problem and stressfree.

Side note- drove the car on a number of occasions since the light came on and now I realize I was driving around with NO FAN AT ALL. Proving indeed that as long as the car is moving and its' not 90+ w/ AC on, the car doesn't even need ANY fan. Kind of impressive.

But also kind of making me thing about finally sucking it up and installing that extra fan controller I've had for years sitting on the shelf collecting dust.

[StRaNgEdAyS]

Good to know since I was considering an 88° T-stat with my M62B44 spare engine build next year.

Absinthe makes the tart grow fonder

[JimLev]

GG, just saw your PM with a link to this post.
Sorry about the overheat. I won't bust your nutz.
I always want a second fan JUST incase....think you now know one of the reasons why.
Hope your head gaskets and hoses survived.

[Uturn540]

Sorry to hear about the overheat. Hopefully you caught it before it got too hot. I guess it makes for a good argument for recalibrating the temp gauge. I am waiting for winter time to see if the 08xB/139 code shows up on mine to see if it can be verified if it is truly just a later model issue.

[philly98540]

Oh siht. How hot did it get? Who would have thunk the dme would kill the aux with a stat error. Damn over achieving German programmers. Like Jim, I'm in the camp of two fans is always better than one.

[dannyzabolotny]

And this is why I keep my clutch fan. I don't trust the aux fan to always do the job, especially in the crazy Arizona heat.

[geargrinder]

Sorry to hear about the overheat. Hopefully you caught it before it got too hot. I guess it makes for a good argument for recalibrating the temp gauge. I am waiting for winter time to see if the 08xB/139 code shows up on mine to see if it can be verified if it is truly just a later model issue.

Yeah Roy did you see my note in other thread? I am super curious about variations in the behavior of these cars around the t-stat and the gauge at this point.

And yeah. That's exactly it. The recalib'd temp gauge and alarm definitely were in my favor in this case.

I saw it leap towards the top end of the gauge for a second but then shut it down. Watching how fast it cooled off even turned off, I am guessing that's the aux water pump feature of these cars and if so it's tremendous. I have a few drips of dried residue in the engine bay so I think it vented a tiny bit of coolant but not much, no coolant level warning or anything.

It was all too hectic (struggling to get off the highway in brutal traffic to a place to park, dog in the back, angry boston drivers everywhere...) for me to even consider getting KTMP on the cluster so I cant say exactly how hot it got but because I re-scaled the temp gauge, 'top of gauge' is now not 'engine is toast', the way BMW sets them up from the factory.

[geargrinder]

Who would have thunk the dme would kill the aux with a stat error. Damn over achieving German programmers.

Yeah. As soon as I saw it do that, the 'logic' was clear to me.

But its crap logic.

Yes running dead cold open t-stat is terrible for an engine.

BUT, the fan runs off a much higher temp threshold than 'cold'! Even w/ a dead-stuck-open t-stat, the Aux fan wouldn't / shouldn't activate its 'normal logic' until the coolant coming out the radiator is HOT, dammit!!!! So there's no reason to 'kill the aux fan'!!! Both systems are far more robust in terms of fail-safe if they run independently in parallel! If the t-stat is stuck open, the Aux fan shouldn't ever trigger anyway unless the engine starts to overheat! It's a false logic there...

Dumb German programmer in this case.

Yep, thinkin about finally adding a puller fan back in now. Although damn the Aux works just fine on its own, the minute it fired back up I drove for another hour in the same traffic and all was hunky and dory.

[Ed CT]

Wow. Hope no serious damage happened. Your re-scaling the temp gage may've saved the day.
I don't have an M62 but you got me thinking that I haven't heard either of my fans run lately (aux nor the viscous clutch jet engine). May be a good time for all E39ers to check their fans' health.

[peter540]

Sorry to hear about your probs with the thermo setup, GG.

And to jinx myself, I, with an '03 w/the 88° thermo, had been having SES issues since switching to that thermo in December, as you may recall. This summer, though, no SES, with KTMPs between 94° and 99° -- Atlanta summer highs were in the 90s, and even now we're in upper 80s, and I think that's enough to bring the KTMPs to more acceptable levels for the DME. I fear that I'll get the SES again as I approach emissions-inspection time in the cool of March.

I'm running the Zionsville setup with the electric fan. Also, my AUX fan had been working fine with the AC.

Is it possible that in my case the thermostat has "loosened up" a little, leading to slightly higher KTMPs? Could that have been similar in your case?

[XAlt]

I think this calls for the most practical puller solution.

woooooooooooooooooooooshhh

[JimLev]

I think this calls for the most practical puller solution.

woooooooooooooooooooooshhh

Or maybe a hack on the temp sensor in the lower hose (tu motors) to get the aux fan to come on at a lower temp.

[philly98540]

Or maybe a hack on the temp sensor in the lower hose (tu motors) to get the aux fan to come on at a lower temp.

Interdasting! Would control the aux better with the lower stat. Don't think it will help with the Pee code though...

For my non vanos, i can just get a lower dual temp switch from an e36 318, but for TU, the dme controls the pwm to the aux based on rad outlet temp. Fake the resistance a bit to trigger the aux faster at a lower temp. Or find a way in the code to do it. I think skitzo or someone did this already.

[RuskiE39]

Must be nice having a functional aux fan

[StRaNgEdAyS]

Must be nice having a functional aux fan

Them feels

Absinthe makes the tart grow fonder

[HoZy]

Good to know since I was considering an 88° T-stat with my M62B44 spare engine build next year.

Absinthe makes the tart grow fonder

Don't worry, ours don't log this crap.

85c tstat for 4years now.



Also, geargrinder.

Your symptoms sound like a weird coincidence and not the actual culprit.

Cheers
Mat

[dovlet]

It is a good thread but may i add my expirience with 88 t-state. I have 2002 540i with the same 88 t-state. We have here in Turkmenistan about 45-50 degree. When I am driving as usually with AC my engine is showing 90 degree and fan is working always. As soon as I switching off my AC fan is stopping and starting to work only after my engine reaches 105 degree. I know 100% that in ECU there is place where we can change FAN starting temperature. If some tuner will spend his time to make amendments in ECU map the problem will be solved.

[Uturn540]

Yeah Roy did you see my note in other thread? I am super curious about variations in the behavior of these cars around the t-stat and the gauge at this point.

And yeah. That's exactly it. The recalib'd temp gauge and alarm definitely were in my favor in this case.

I saw it leap towards the top end of the gauge for a second but then shut it down. Watching how fast it cooled off even turned off, I am guessing that's the aux water pump feature of these cars and if so it's tremendous. I have a few drips of dried residue in the engine bay so I think it vented a tiny bit of coolant but not much, no coolant level warning or anything.

It was all too hectic (struggling to get off the highway in brutal traffic to a place to park, dog in the back, angry boston drivers everywhere...) for me to even consider getting KTMP on the cluster so I cant say exactly how hot it got but because I re-scaled the temp gauge, 'top of gauge' is now not 'engine is toast', the way BMW sets them up from the factory.

Got your note, responded, and going to do some testing and research next week after I get the AC repaired. Also, just pulled the Bentley and surprise. There is no 139/P0138 code shown prior to 09/01/02 production date. That would explain the issue occurring only on later models. There is also no 123/P0125 code Insufficient Temperature For Closed Loop Fuel Control.

[geargrinder]

Or maybe a hack on the temp sensor in the lower hose (tu motors) to get the aux fan to come on at a lower temp.

Yeah Jim except the fan activation temp isn't the problem. Its the engine seeing the dual-temp being too low, throwing the code, and not running the Aux fan.

However the idea is correct, w/ the lower engine temp you do prob want the fan to run at a lower temp to help keep up w/ the increased radiator load and lower the return-temp more than before.

Or find a way in the code to do it. I think skitzo or someone did this already.

If some tuner will spend his time to make amendments in ECU map the problem will be solved.

Chris/Dov - yeah, Terraphantm has apparently found the value and done this for a few guys. I assume Frank should be able to do it easily as well.

I've been working on trying to make these changes but with my weirdo tune its taking me longer than it should to figure it out. Terra is trying to help me a bit but it may be more than he wants to bite off.

The idea is..
1. lower the error temp threshold so the DME doesn't throw the code.
2. separately lower the Aux fan activation control to reduce coolant return temp thresholds

Your symptoms sound like a weird coincidence and not the actual culprit.

Sure Mat I could buy that if it wasn't for the fact that the car has been on/off many times and even during my overheat event I started/stopped it a couple times, no Aux fan. The minute codes were cleared instantly was back and running 100%.

Believe me I was convinced I just had a dead Aux fan.

I will for sure re-confirm that when I get the code again and post back here but it was too exact to be coincidence... even if I hadn't 'sorta noticed but not noticed' the fan wasn't running before I wouldn't be so sure of it, but I am pretty confident the fan stopped running when I first got the SES and was too busy/lazy to clear it right away.

- - - Updated - - -

BTW with some overnight rumination, it may not be intentional disabling of the Aux fan even... Does occur to me could just be a straight up bug / unintended behavior. Although I could see the logic some engineer might think up if he didn't think it all the way through.

[geargrinder]

Got your note, responded, and going to do some testing and research next week after I get the AC repaired. Also, just pulled the Bentley and surprise. There is no 139/P0138 code shown prior to 09/01/02 production date. That would explain the issue occurring only on later models. There is also no 123/P0125 code Insufficient Temperature For Closed Loop Fuel Control.

Good stuff boss. Nice research.

[tptrsn]

Anyone have any ideas what the german wording for aux fan is?

[geargrinder]

Could be E-Lüfter or something like that. Of course knowing Bosch the keyword will be some inscrutable acronym that even a German would not have any idea about like "KUWASSUTKENNEL" for 'cooling water electric fan over temp curve'
'

[philly98540]

^yup

[tptrsn]

Haha, no doubt! Next time I'm poking around I'll see if I can find anything (Bosch). I have had good luck so far with reprogramming my thermostat to 88C, but I would like to activate the aux fan lower for next summer. Judging by today's cold Michigan weather I may have no further concerns this year...

[philly98540]

Thad. You and I are non vanos so aux fan is purely controlled by switches and relays. No dme nannies.