[RockCrusher]

No pics unfortunately.

But on an "interesting" road on the way home and enjoying myself and the car but not to the max by any stretch came to where I turn off and downshifted -- manual transmission -- several gears and made the turn with no drama and at a safe/sane speed.

As is my habit I switched A/C off and bumped fan speed up a click to dry the A/C hardware.

Directed a glance at the engine info display. Coolant temperature which had been at the 212F point for miles was way down to around the 150F mark. Checked oil temperature and it was about 212F and this is where it had been for miles.

No signs of any engine issues. No sign of any coolant leaks.

Drove on and the coolant temperature came up faster than it comes up from a cold start. But it didn't jump up and I believe didn't come up as fast as it had dropped.

With cars with coolant temperature gauges or using an OBD2 tool to view coolant temperature in real time I have never seen such a large change in coolant temperature with any car like what I saw with my BMW.

Don't know what to make of what I saw. Tomorrow (or maybe later this evening) I'll retrace the last 10 miles or so of my drive home today and drive pretty much the same way and this time be more observant and see what I see...

[cmgbk75]

Originally Posted by RockCrusher

No pics unfortunately.

But on an "interesting" road on the way home and enjoying myself and the car but not to the max by any stretch came to where I turn off and downshifted — manual transmission — several gears and made the turn with no drama and at a safe/sane speed.

As is my habit I switched A/C off and bumped fan speed up a click to dry the A/C hardware.

Directed a glance at the engine info display. Coolant temperature which had been at the 212F point for miles was way down to around the 150F mark. Checked oil temperature and it was about 212F and this is where it had been for miles.

No signs of any engine issues. No sign of any coolant leaks.

Drove on and the coolant temperature came up faster than it comes up from a cold start. But it didn't jump up and I believe didn't come up as fast as it had dropped.

With cars with coolant temperature gauges or using an OBD2 tool to view coolant temperature in real time I have never seen such a large change in coolant temperature with any car like what I saw with my BMW.

Don't know what to make of what I saw. Tomorrow (or maybe later this evening) I'll retrace the last 10 miles or so of my drive home today and drive pretty much the same way and this time be more observant and see what I see...

Do you get the coolant changed like your oil?

[Squidget]

I mean, coolant doesn't magically get better nor do radiators magically radiate more heat at a given flow rate.

So I'd guess one of two things:

1) malfunctioning coolant thermometer.

2) coolant valve stuck open, causing coolant to flow through radiators faster.

I figure #1 is far more likely. In either case I'd expect a code to get thrown.

All guesses, I'm no mechanic.

[Squidget]

Also, I must say this is assuming you haven't lost any coolant.

You said no obvious leaks, and I assume you would also notice if coolant infiltrated into your cylinders via head gasket (white smoke!!!).

Because that would be a cracked head gasket and extremely extremely bad. And also should have thrown a code.

Priority one is confirming you have all your coolant and it's not leaking into the engine.

[Squidget]

I also realized I forgot to ask the most basic question. Are the coolant temperatures stable at the expected temps? This COULD just be the computer calibrating its systems over time.

Everything auto-tunes and calibrates using software now. It can be hard to know what "normal" is, since it can change over time.

[RockCrusher]

Originally Posted by cmgbk75

Do you get the coolant changed like your oil?

No. Just engine oil/filter and diff fluid as per the 1200 miles "break in" service.

Just returned from another drive.

The drop is real. Caught it on video with my iPhone. In about 90 seconds the temperature drops from "210" (the end of temperature bar starts out just under the '0' of "210") and stops to just the right edge of the '0' of the "150". Drops pretty fast. Then it begins to climb again. This takes longer but the video of this is 1 minute 26 seconds long albeit I missed the first handful or so seconds of the start of the temperature drop.

Saw this happen several times.

As for what triggers this I'm sort of thinking it begins with a moderate acceleration up to (legal) freeway speed then once reaching the posted limit and engaging cruise control.

While the bar is indicating the temperature is moving from just over 210 down to close to 150 seems like a lot of temperature change one can't know from the graphical display just what the actual numbers are.

In my collection of automobile stuff I have a trip/data logger I can plug into the car's OBD2 connector and data log among other things coolant temperature.

Also, I have an OBD2 scan tool I can plug in and view in real time coolant temperature so I can put some actual numbers to what I'm seeing. The scan tool can log data but I don't have a computer with the necessary serial port to connect the scan tool in order to download the data to I guess a spreadsheet.

Tomorrow I'll do some data viewing.

[RockCrusher]

Originally Posted by Squidget

I also realized I forgot to ask the most basic question. Are the coolant temperatures stable at the expected temps? This COULD just be the computer calibrating its systems over time.

Everything auto-tunes and calibrates using software now. It can be hard to know what "normal" is, since it can change over time.

No signs of any coolant leak. No water vapor from the exhaust. No odor of anti-freeze from the exhaust. And I had the car in today for its break in service and the tech checked all the fluids and found nothing low. He also went over the car -- he had the car around 2 hours -- and the car came back with a clean bill of health.

I don't think there is a leak. I don't think there is a problem albeit the apparent amount of temperature change is a bit much. But other cars have manifested a good 30+F swing in coolant temperature with coolant temperature climbing as I drive in town the dropping when I get on the freeway.

The coolant temperature once the engine reaches operating temperature appears pretty stable until of course it drops rather dramatically.

It doesn't climb above the 210-ish temperature though so it is not a T-stat sticking partially closed. I can't hear the radiator fan but the A/C is on -- it was 81F earlier this evening when I went out and caught the behavior -- and the radiator fan probably is running all the time. The temperature of the air from the A/C vents was quite cool -- I had auto climate temperature set to 72F -- and I detected no change in temperature nor the sudden appearance of clammy air that signals the A/C is no working at any time

No check engine light. I didn't see any warning symbols lit up nor did I see any messages. Tomorrow I'll look to see if there are any messages logged but not displayed.

[Squidget]

You've reached the limits of my knowledge and done all the diagnostics I can think of. I can help you no further, sorry.

Good luck, I hope it's just Software being Software and not a problem!

[JustinHEMI]

Interested to see results! Good luck in troubleshooting!

[RockCrusher]

Originally Posted by Squidget

You've reached the limits of my knowledge and done all the diagnostics I can think of. I can help you no further, sorry.

Good luck, I hope it's just Software being Software and not a problem!

Absent any further untoward behavior right now I don't think there is a problem and this includes any leak.

What I'm seeing has in some respects the earmarks of being just an idiosyncrasy.

I'll collect real numbers so I don't have to guess at the actual temperature swing high/low numbers.

More when I have more to add.

[RockCrusher]

An update of sorts...

Using an OBD2 scan tool what I observed once the engine was up to temperature indicated by the coolant being at the 210F point and oil temperature the same is after a bit of hard acceleration in 3rd gear on the freeway -- traffic limited the amount of acceleration I could do -- I observed the temperature dropping from 215/216 down to 185F then coming up again as the hard acceleration was over and I had resumed steady state cruising.

It appears to me the drop in temperature is in response to the hard acceleration almost as if the engine controller has started the process of dialing down the coolant temperature in anticipation more of this hard acceleration, spirited driving, will continue and the actual temperature drop lags a bit.

In my case because I can't continue to drive like I am on the track the temperature continues to drop for a few more degrees then changes direction and begins to climb again and is soon back to the normal operating temperature.

BTW, with my car the first gap in the coolant temperature bar the gap between 150 and 210 is 185F. The gap almost under the 210 is 215F. I observed no coolant temperature above 218F which is a few segments of the bar to the right of the gap.

[DomMuc]

normal temp management... b58 has same "drop" ...

[blue135]

I think there is nothing out of the ordinary with the coolant drop related to more aggressive engine operation. Man 2008 135i will do exactly the same thing under the conditions you describe.
However, my numbers tend to run a narrower band. Warmed up, it will go from 215 down to 195 then come back up. Again, using an OBD coolant monitor.
I think this comes from the computer altering the speed of the water pump, but that is just my theory.

[KC87ZB]

I don’t believe you have an issue, even my X3 does this. It is the cycling of the thermostat and coolant pump. It will be more noticeable depending on ambient and driving conditions. I’ll check my M2 sometime soon but I bet it does it too.

[RockCrusher]

Yes, looks to be normal behavior. That is intended behavior.

Installed a trip/data logger last night. But unfortunately the device doesn't work. It is old and the internal battery which powers the clock and critical storage memory has run down. The device connects to the car, and the speed threshold works -- it beeps if I exceed 75mph (the default setting which I left alone for now) -- but when I went to download the data there was none. I won't bore you with a lot of tech-y talk as to why this is the case but right now trip/data logging using this plug in device is not available. (I have 3 of these. One is just dead. The 2nd one I suspect has the same dead battery as the one I tried last night and will act the same.)

Oh, these devices are >15 years old and this is past the battery's expected service life.

Still believing the trip logger would work I hit the freeway and with room to make some hard pulls it was obvious -- glancing at the coolant temperature display on the dash -- the drop in coolant temperature was in response to the hard acceleration and increased heat load that would arise from this.

[autoaddictUS]

I'm glad to read that someone else's M2 is doing this. The gauge movement appears more dramatic than what the actual temp fluctuation is after watching my scan tools graphing function.
Same thing though as OP, after going into boost it drops to 175 ish then back to 210 or so with easy driving. Both coolant reservoirs are at the max level and no cel, smells or visible leaks/residue.
Oil temp and coolant will peak over the middle segment occasionally. Outside Temps are between 75-95 with high humidity.
I didn't notice it until I set the center display on the boost pressure and coolant temp indicators which maybe most people don't select as often.

[M2siast]

As mentioned before, this is completely by design for efficiency and power management.
Has been this way for over a decade.

Nothing wrong, albeit “interesting” operation.

[KevM2]

Yes I’ve noticed the same changes to engine oil temperature with hard accelerating and I believe it kicks the water pump into fast mode just like how sport+ mode turns the water pump into “overdrive” in the F87 but the F87 doesn’t show independent coolant vs oil gauge, just a “combined” gauge…. but what I don’t understand is how oil temperature can can drop without an initial drop in coolant temperature… it’s almost a paradox…

[aerobod]

Originally Posted by KevM2

…. but what I don’t understand is how oil temperature can can drop without an initial drop in coolant temperature… it’s almost a paradox…

The oil cooling circuit has its own thermostat and radiator and the oil pump has a dual chamber design that can control delivery volume and pressure independently. The oil cooling is relatively de-coupled from the engine coolant cooling in the S58 compared with many engines.

[KevM2]

Originally Posted by aerobod

The oil cooling circuit has its own thermostat and radiator and the oil pump has a dual chamber design that can control delivery volume and pressure independently. The oil cooling is relatively de-coupled from the engine coolant cooling in the S58 compared with many engines.

Now that makes sense!! Thanks for that explanation