In case your New Year resolution is to lower coolant operating temperature...GroupBuy

[mxchris727]

I agree that the temperatures directly influence the failure of seals and plastic components; that's why so many newer cars have issues with timing guides. My N54 runs the exact same temp as my M62TU (105-108C), so I never really thought of it as an issue. However, I remember watching a video awhile back where someone solved the VANOS diesel sound with a lower temperature thermostat (although my engine makes no noise). I am planning on doing a VANOS/timing overhaul this summer; maybe I'll stick with the 105C thermostat for now. I can completely understand the need for a cooler one if auto-crossing or driving aggressively often.

Thanks Geargrinder for the chart, interesting perspective of cold start wear! It proves the fact that most wear occurs at startup.

[BMW540san]

What is the normal operating temperature that everyone is seeing with these? I'm on the fence; I never get anything but OEM/correct parts for my cars. Would the lower engine temperature increase engine wear?

I think GG said it nicely in his post. Here are my thoughts:

1. More heat equals more pressure and our plastic components ( radiators, hoses exp. tanks etc..) are failing relatively early due to the combination of the 2.
2. Better fuel economy and cleaner emissions? I'm yet to have any problems passing emissions and seeing that better fuel economy. Sure, it's probably true but to what degree?
3. When you running 105 C you're much closer to the 115 C where things can get serious in a hurry.
4. One of the most reliable BMW engines, M52, is running on conventional 92 C thermostat (or 88 C) and it literary last forever.

So, no, thank you BMW engineers, but I went back to conventional thermostats on my 540 and X5 and I'm doing just fine. Also, rare but it did happened, few owners had nightmares when map controlled thermostat connector started leaking coolant and it went to all the way into DME box and made quite a show. Even if that's internet rumors, there are cases failing factory thermostats due to coolant leak at the electrical connector.

Now if we want to talk about too cold, we should mention E39 M5 thermostat that opens at 72 C (I believe). Now you can make some arguments there about engine being too cold.
But of course, as long as you drive E39 M5 the way it's meant (hard, but properly warmed up first) you have no issues. I drive all of my cars hard at times and I feel better with "colder" thermostats.

[Da Beemers]

I do not see temps go above 100c anymore with the new thermostat and my car likes it. Watching it climb as high as 113c with the OE thermostat used to really worry me, it was like waiting for something to explode. It's bad enough that we have to deal with the crazy buffer zone on the temp gauge, but adding to that a borderline explosive running temp is too risky to me. The way I see it, for anyone that has one of these engines and cares about it long term this mod is a must. The best part to me is that it is a real BMW part.

[geargrinder]

Totally agreed w Philly and a huge miss by me to not mention the other non-metal parts.

That chart is all well and good for the metal parts like pistons and cylinder walls and journal bearings but a plastic temp-vs-fatigue-life chart would be very very different I'm sure.

[Flounderasu]

What is the normal operating temperature that everyone is seeing with these? I'm on the fence; I never get anything but OEM/correct parts for my cars. Would the lower engine temperature increase engine wear?

I got a BMW one.

93C is pretty solid on KTMP #7 at this time of year in AZ. This might not be true temp IMHO - I'm seeing radiator outlet temps in the high 70's-80's via INPA.

Summer in AZ - no AC it will fluctuate from 93-99C in the city and Aux fan typically comes on and drives it down or my mech fan since I still haven't gotten around to finishing my e-fan stuff.

HWY - AC on, I see solid 95-97C. HWY and no AC 94-95C.

MPG has dropped about 1-2MPG but I also did the M60 intake downgrade/swap at the same time.

[peter540]

Quick update. I'd thought the band clamp had failed on the upper hose. Turns out the plastic failed. It didn't separate all that much on its own, but when I pulled on the hose with minimal force, it separated. Guess that would be the source of the faint coolant smell that I kept noticing but not finding.



The hose was old-ish -- about six years old -- but only had about 50k miles on it. We live in the Southeast, and the car has run on hot Alabama and Georgia summers.

This seems to be further evidence of what the car's running hot with high pressure in the cooling system can do to components, especially those made of plastic.

Glad I bought all three radiator hoses. Any hoses with plastic parts will be new, and with the Zionsville and New 88° thermostat, I'll have much more peace of mind.

--P

[peter540]

And the thermostat is in! No SES SES while burping the coolant; maybe I'll get lucky. Also did an oil/filter change and rewired one of the electric fan wires.

ForumRunner_20170110_061638.png

Today, I'll road test everything.

--P

[geargrinder]

For the record yet AGAIN... a thermostat code doesn't set a SES/CEL - lack of light doesn't mean lack of code.

Now truly - even having the code may not matter at all - as long as it doesn't block emissions readiness in scan-jurisdictions and doesn't otherwise impair the DME into a limp mode or anything (no evidence that it does) it well might be totally fine to drive around w the code lurking behind there anyway. But a t-stat code does NOT set a light.

[peter540]

For the record yet AGAIN... a thermostat code doesn't set a SES/CEL - lack of light doesn't mean lack of code.

Now truly - even having the code may not matter at all - as long as it doesn't block emissions readiness in scan-jurisdictions and doesn't otherwise impair the DME into a limp mode or anything (no evidence that it does) it well might be totally fine to drive around w the code lurking behind there anyway. But a t-stat code does NOT set a light.

Easy there, GG. I forgot, but cut me some slack -- I pulled an all-nighter getting all of this done and am not fully on my game at the moment. But also, in all seriousness, thanks for all the great info.

I'm just glad to have the new thermostat in there, and I'm ESPECIALLY glad to have replaced all the radiator hoses - the upper one's housing was shot (browned and crumbly) at roughly 55-60k miles of use. Granted, they were also nine years old. Maybe the next set will hold up better with the 88° thermostat.

That was a cold night's work -- lower 30s, no heat in the garage. I'm hopeful I can wait until spring for the big project (clutch, JBR flywheel, rear suspension overhaul, M5 diff swap, perhaps muffler delete w/Vibrant muffler as replacement). Car will be of the road up to two weeks while I tackle all that stuff.

--P

[geargrinder]

Not ranting at you Peter... it's just something that doesn't seem to lodge... Glad you got all your stuff back together and sorted. What parts did you go with on the hoses in the end?

You picked a crap time to do garage work in Atlanta BTW! The one time you guys get a big snow / ice dump a year?

Seems like cooling systems are just a constant item on these damn cars... I started to see some small intermittent coolant drips again on my car and thought it was the 2yr old expansion tank crapping out again (and of course that is sadly completely plausible) but after investigation I'm pretty sure it was just the crappy buna rubber o-ring on the bleed screw. At least I hope it was - it was pretty flattened out and all the leakage seemed to be just coming from up around the bleed screw. I replaced w/ a nice green viton and waiting to see if that fixed it or if indeed I still have an expansion tank curse. First few heat cycles on it look good but will have a longer drive session this afternoon.

BTW - I may have some more info later but I am analyzing some testo logs I ran last week and indeed it seems w the 88 T-stat I also have more or less a solid 93F now when all is up to operating temp.

[peter540]

TELL me about it. Crap time indeed to do this work -- cold coolant in child weather is especially no fun to deal with.

I ended up going with genuine BMW hoses. The stealer matched FCP Euro's price and I was able to pick them up the afternoon before the storm hit. I needed all the parts in hand, so I'm also thankful that Z was passing through ATL last week and could get me the tstat.

Every time I deal with cooling components, I thank myself for the decision I made six years ago to ditch the BMW radiator and expansion tank and clutch fan for the Zionsville setup. Nice not having to worry about a ruptured plastic piece. If there were similar alternatives for the hoses, I'd eagerly go that route, but alas, I must make do with hoses that have plastic housings.

Looking forward to seeing what you find with the operating temps using the 88° tstat. I think the switch is going to prove especially beneficial down here in Hotlanta, where the temps in the summer can be quite, well, hot.

--P

[JimLev]

Peter, with the lower temp T-stat your cooling system pressure will be about 5 PSI lower, the hoses will last a long time.
Back in 2004 my top hose split. After doing the controlled voltage to the t-stat heater my avg KTMP is <90C almost all the time with the pressure reading around 13PSI.

[peter540]

Peter, with the lower temp T-stat your cooling system pressure will be about 5 PSI lower, the hoses will last a long time.
Back in 2004 my top hose split. After doing the controlled voltage to the t-stat heater my avg KTMP is <90C almost all the time with the pressure reading around 13PSI.

Yes, I feel very good about the peace of mind, if nothing else, that this mod will give me...

--P

[philly98540]

For the record yet AGAIN... a thermostat code doesn't set a SES/CEL - lack of light doesn't mean lack of code.

Now truly - even having the code may not matter at all - as long as it doesn't block emissions readiness in scan-jurisdictions and doesn't otherwise impair the DME into a limp mode or anything (no evidence that it does) it well might be totally fine to drive around w the code lurking behind there anyway. But a t-stat code does NOT set a light.

Not true in all cases GG! My car lit up the CEL for the stat code. I've said this multiple times. Seems like there is slight differences in our cars. Some get the light, some don't. Not sure if its TU vs non Tu thing, or is is some other variation in the versions on the DME's.

[Mach540]

I'm "pretty sure" mine set a CEL also. "Pretty sure" because my CEL has been disabled by a PO, but my scanner said there was a CEL for the MAP cooling error. P1622 or something like that.

Regarding temps, mine runs a fairly consistent 93C. +- 2C max

And my radiator pressure runs at 8 psi, compared with 15-18 psi when at 108C.

[geargrinder]

Not true in all cases GG! My car lit up the CEL for the stat code. I've said this multiple times. Seems like there is slight differences in our cars. Some get the light, some don't. Not sure if its TU vs non Tu thing, or is is some other variation in the versions on the DME's.

Sorry chris - i was talking more the other side - the guys arguing over and over that since they have no light they have no code (but havent scanned...). I agree it seems like the late cars are the ones where a code wont necessarily set a light. Wonder if its purely ME5 vs ME7 or if its more like the facelift changes...

[geargrinder]

Interestingly my car threw a thermostat code today, and, lit an SES.

I don't have the number handy but it was the undertemp code that means the dme thinks the t-stat is jammed open because the temp is too low.

Not sure if that's just a freak misinterpretation of the lower engine temp mod, or if I have a temp sensor issue... I think both mine (block and rad) are orig on this car. Don't think the brand new t-stat is an issue...

Cleared and and didn't come back for another 1.5hr of driving so it's a monitor situation, not too worried. But curious.

[philly98540]

That's definitely a freak thing. Code for missing stock stat heater is not that. Usually something like "thermostat final stage" or something like that.

View ktemp for a bit to make sure it's getting up to 90.

[geargrinder]

Yea Chris I got a lot of testo logs now - seems to be reliably 92-94 area, although as mentioned it does heat up a tad slower. Maybe it is a little leaky / not sealing ... But I also found some posts saying that code on M54's is sometimes temp sensor drift too. Not worried from what I'm logging but I'm gonna keep monitoring.

[philly98540]

Sounds good

[BMW540san]

My X5 would throw that same code when temp was mainly under 90 C. I do have 95 non vanos thermostat in it with modified hose.
Ever since I figured it out that temp sensor is acting up and replaced it, temp is back to around 95 and code is gone.
I imagine that code could pop up on cars with 88 C during winter where it might run 86 - 88 but it's probably because DME is programmed to see mainly 105 C

[geargrinder]

Good info. Thats' what the M54 threads seem to say. And that it can be intermittent as the sensor starts to fade... My sensors are all orig so no big to do a replacement there. I've run the car for thousands of miles with the T-stat and resistor and not a hint of an issue until now so I'm leaning towards 'something else' like that and not too worried about my main setup.

[Austrianvespagu]

Older thread, but I'm looking to do this on my '00 540i but when I check the resistance of the stock Tstat heater element, it seems to be 2.4k Ohms. I've quadruple checked, different multimeters, both directions in case the was a diode in there, etc. It's definitely 2400 ohms, which is WAY different than the 10 ohm resistor value I normally see recommended. Also, seems to me that the Tstat still works properly, no codes, and even if the heat was dead, wouldn't one expect to see either a 0-ohm short or infinite resistance of an open circuit? Anyone have any ideas on this strangeness? Thanks!

[geargrinder]

As I mention on page 1... I can tell you that the element I took out of one even had the ohms printed on it. 10 or 12 or whatever it was. Is yours an aftermarket thing? I don't think you can conclude that a failure would be 100% open or short by the way. Lots of resistive parts "drift up" with age. I'll grant you drifting up 20000% seems highly unlikely tho.

[Austrianvespagu]

Thanks Geargrinder, I suppose that's true, and I'll try and see if it's an AE unit, maybe that's the explanation. Either way, I'll still just plan to use a 10ohm ~2 watt power resistor when I put the new 88C part in there. Thanks for the reply!