Rapid Coolant Temperature Drops

RobX5 · 03-01-2023, 06:55 AM

2016 X5 sdrive25d 77,000km. Fluctuating coolant temps (see PDF attached)

Why are coolant temps dropping so quickly under load? In some instances, the temp drops from 91 deg down to 78deg in 15seconds.

New OEM thermostat installed
-previous thermostat was soft failing and regulating at 82deg sustained on highway drives and also slow to warm up.

New thermostat now regulates to 88-90deg C but only after at least 25mins of driving. Heats up quickly when stationary at IDLE but as soon as I accelerate, it'll drop into low 80s. The car will stay in the high 70's low 80s if driven under load, only rising when off the accelerator / coasting.

Is there a secondary cooling circuit open- transmission oil cooler thermostat? ISTA+ test on the EGR changover valve test is good (I can hear the valve clicking).

Chilled · 03-01-2023, 05:21 PM

What did you use to log the temps?

RobX5 · 03-01-2023, 05:22 PM

BimmerCode. And then plotted using excel.

Chilled · 03-01-2023, 05:34 PM

Cheers, There is a thermostat for the trans cooler and its on the transcooler. Not sure how it been open would affect the water temp tho.

Here, sounds vaguely like a similar issue.
https://f15.bimmerpost.com/forums/sh....php?t=1993370

If you are not getting any error codes, is it really an issue. I personally would love to have this low water temp problem, and not be sitting at 100ish constantly.

ciscorob · 03-02-2023, 02:49 PM

Like Chilled said, it may be possible this is caused by a failed thermostat for the trans cooler or, perhaps, your sensor is starting to act weird?

RobX5 · 03-04-2023, 10:14 PM

Thanks for the replies- I do find myself asking the question now is it even a problem. It’s probably not worth the effort. I was troubleshooting poor mileage and stumbled on soft failing thermostats, which this car had. Changing it didn’t produce the expected results. It certainly doesn’t behave like my b47 engine in my f30 320d; the coolant temps are rock solid at 88-92 and don’t budge under acceleration. Today I found the coolant temps hovering at 82deg at highway speeds after an hour of driving… I may try changing the coolant sensor.

RobX5 · 03-04-2023, 11:21 PM

Drove the car for over 2 hrs - max trans oil temp is 85-86 when eng oil is stable at 92-93C. Is that a soft failing thermostat in the oil cooler? I would’ve thought it’d get up to 88+.

Chilled · 03-05-2023, 05:33 AM

Sorry it's a little confusing? Which temps do you have issues with and/or are too low?

If your trans is in the low to mid 80C°'s whilst on cruise, that is perfectly normal. You trans temp will always be lower than the engine oil. If you are doing a Nebo run, constantly chopping gears and its still in the 80s. Then you may have an issue.

Seen low-mid 90C°s on the engine oil is perfectly fine. If it was constantly at 100C°-ish, that would be a concern. Unless your stuck in traffic. Then its ok.

As far as coolant(water), seen it just over 100C° is fine and I've had mind swing from 105 - 95 in about 30 seconds. Was stuck in traffic and then started to move.

I don't know the specs for the diesel, but your temps seem fine. Usually most people try to get their temps down. As its the high temperature that kills things.

Btw, if you do end up pocking around in ISTA/code reader. Please let me know if you can find a value for the electric water pump.

RobX5 · 03-05-2023, 02:10 PM

The issue I’m chasing is the rapid coolant temp drops which seem a little extreme. I’m trying to figure out if it’s ‘normal’ to have drops of 8-9C is less than 5secs when accelerating at normal rates from a stop. I can also drop the temps from 92 to 78-80 in 5-10s just by selecting a low gear and high rpm. It doesn’t seem right. The car warms quickly to 70’s, but then takes a long time to get into 80s (>25-30min) which makes me suspect oil cooler thermostat is open partially after having changed the main thermostat. This f15 doesn’t have an egr thermostat or map thermostat like many other posts discuss with coolant temp issues. Other than that I’ve got a failing temp sensor, or I don’t have an issue at all?

From what I can gather from all the threads out there on coolant temps, the DDE is super sensitive on low coolant temps and need to get and stay up in 88-92 range. Whilst my average final temps are fine for avoiding the more serious issues (stuck in warmup modes, glow plug activation <75 and prevention of DPF regen <60), I can’t help think the system is not functioning as intended and causing some inefficiencies. I don’t want this thing to run any hotter, just would like it to be stable as per my 320d. In my mind it’s a fine line between over cooling and running hot, but I’ll take over cooling any day!

Re water pump- couldn’t find anything in ISTA. Found a thread with INPA displaying pump speed values, but pump is unlikely to
show any codes until it is failed. Also bled the coolant a few times to check if there could’ve been some air bubbles causing the temp drops, but no change.

ciscorob · 03-07-2023, 06:03 AM

What is the data logging rate? If you're only updating at larger intervals then your values could appear to "swing" because the sample rate is simply updating slower than what is being read. Other than the sampling rate of the data logging you're receiving it could be a sensor that is going nuts and, at least for those of us with an N55, the oil and coolant temp sensors are not only inexpensive, but easy to replace.

RobX5 · 04-02-2023, 11:54 PM

Sampling rate is quite high (somewhere around 3-4hz).

Update- I’ve since had water pump replaced as mechanic suspected possible internal damage which may have been inducing air into system (air over sensor resulting in drops?). Also had the EGR deleted and ECU remapped. Turned out the pump had some signs of internal failure, but it didn’t fix the issue. This is an upgraded pump (internals metal vs plastic?).

Driving on the highway for over 40mins, the coolant temp never got above 72-74deg. Yet would rise quickly to 88-92 at a stop. As soon I’d accerlerate, again the temps would drop anywhere between 8-12deg C in 3-4seconds.

I’m beginning to suspect open thermostat again (it’s brand new and OEM!). At least it’s not as big of job to get to the thermostat now with the EGR and cooler removed. Before then I’ll replace the coolant temp sensor next week.

Chilled · 04-03-2023, 09:49 PM

Are you driving this is Sports mode? Because that opens all the thermostats with the intent of lowering all the temps (coolant, oil, etc)

The OP of this thread managed to resolve his issue. Not sure if the issue is the same. In his case the temp wasn't coming up high enough.Not swining.
https://f15.bimmerpost.com/forums/sh....php?t=1993370

RobX5 · 04-05-2023, 03:03 AM

Quote:

Originally Posted by Chilled

Are you driving this is Sports mode? Because that opens all the thermostats with the intent of lowering all the temps (coolant, oil, etc)

The OP of this thread managed to resolve his issue. Not sure if the issue is the same. In his case the temp wasn't coming up high enough.Not swining.
https://f15.bimmerpost.com/forums/sh....php?t=1993370

Just normal mode. I believe that post refers to models with a MAP thermostat where they are electronically controlled (the element can be heated up artificially and melt the wax). My thermostat is purely mechanical with nothing attached to it, it operates with no input.

RobX5 · 05-06-2023, 10:44 PM

Solved. Coolant temps back at rock solid 88-92. Thermostat was testing fine on stove.

[Symptoms- temp would eventually get to 88 if left at idle, coasting or lots of city driving, but under ANY engine load above 77C, the temp would rapidly plummet 10-15c+ and take a while to get back up again. Any highway driving would cycle 77 max down to 68 repetively]

2 issues -

1/ EGR delete bypass kit. Post this mod, I experience much more severe coolant temp drops. Turns out the egr bypass kit was incorrect for my engine, as it was routing huge amounts of coolant through a bypass hose, likely causing a cooling effect and ultimately bypassing the thermostat in the closed system. Fixed by installing a blanking plate, keeping all coolant in the engine block and warm.

2/original coolant temp fluctuations prior to egr delete which were noticeable (5-6deg) are probably due to air in the system, which is odd considering system was bled multiple times.

Additionally, I was also chasing a rough idle during DPF regens (allegedly normal for this engine- which I still doubt). This problem has since gone post EGR delete- there was definitely something up with the EGR. Happy days.

03-01-2023, 05:21 PM	#2
Chilled Major 364 Rep 1,019 Posts Drives: F85 X5M Join Date: Sep 2021 Location: Tiny Island, Middle of Nowhere iTrader: (0)	What did you use to log the temps?
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03-01-2023, 05:22 PM	#3
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	BimmerCode. And then plotted using excel.
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03-01-2023, 05:34 PM	#4
Chilled Major 364 Rep 1,019 Posts Drives: F85 X5M Join Date: Sep 2021 Location: Tiny Island, Middle of Nowhere iTrader: (0)	Cheers, There is a thermostat for the trans cooler and its on the transcooler. Not sure how it been open would affect the water temp tho. Here, sounds vaguely like a similar issue. https://f15.bimmerpost.com/forums/sh....php?t=1993370 If you are not getting any error codes, is it really an issue. I personally would love to have this low water temp problem, and not be sitting at 100ish constantly.
	Appreciate 1 RobX52.50 Quote

03-02-2023, 02:49 PM	#5
ciscorob Private 16 Rep 51 Posts Drives: 2016 BMW X5 sdrive35i Join Date: Jan 2012 Location: Fort Lauderdale, Florida iTrader: (0)	Like Chilled said, it may be possible this is caused by a failed thermostat for the trans cooler or, perhaps, your sensor is starting to act weird?
	Appreciate 1 RobX52.50 Quote

03-04-2023, 10:14 PM	#6
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	Thanks for the replies- I do find myself asking the question now is it even a problem. It’s probably not worth the effort. I was troubleshooting poor mileage and stumbled on soft failing thermostats, which this car had. Changing it didn’t produce the expected results. It certainly doesn’t behave like my b47 engine in my f30 320d; the coolant temps are rock solid at 88-92 and don’t budge under acceleration. Today I found the coolant temps hovering at 82deg at highway speeds after an hour of driving… I may try changing the coolant sensor.
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Rapid Coolant Temperature Drops

03-04-2023, 11:21 PM	#7
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	Drove the car for over 2 hrs - max trans oil temp is 85-86 when eng oil is stable at 92-93C. Is that a soft failing thermostat in the oil cooler? I would’ve thought it’d get up to 88+.
	Appreciate 0 Quote

03-05-2023, 05:33 AM	#8
Chilled Major 364 Rep 1,019 Posts Drives: F85 X5M Join Date: Sep 2021 Location: Tiny Island, Middle of Nowhere iTrader: (0)	Sorry it's a little confusing? Which temps do you have issues with and/or are too low? If your trans is in the low to mid 80C°'s whilst on cruise, that is perfectly normal. You trans temp will always be lower than the engine oil. If you are doing a Nebo run, constantly chopping gears and its still in the 80s. Then you may have an issue. Seen low-mid 90C°s on the engine oil is perfectly fine. If it was constantly at 100C°-ish, that would be a concern. Unless your stuck in traffic. Then its ok. As far as coolant(water), seen it just over 100C° is fine and I've had mind swing from 105 - 95 in about 30 seconds. Was stuck in traffic and then started to move. I don't know the specs for the diesel, but your temps seem fine. Usually most people try to get their temps down. As its the high temperature that kills things. Btw, if you do end up pocking around in ISTA/code reader. Please let me know if you can find a value for the electric water pump. Last edited by Chilled; 03-05-2023 at 05:43 AM..
	Appreciate 1 RobX52.50 Quote

03-05-2023, 02:10 PM	#9
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	The issue I’m chasing is the rapid coolant temp drops which seem a little extreme. I’m trying to figure out if it’s ‘normal’ to have drops of 8-9C is less than 5secs when accelerating at normal rates from a stop. I can also drop the temps from 92 to 78-80 in 5-10s just by selecting a low gear and high rpm. It doesn’t seem right. The car warms quickly to 70’s, but then takes a long time to get into 80s (>25-30min) which makes me suspect oil cooler thermostat is open partially after having changed the main thermostat. This f15 doesn’t have an egr thermostat or map thermostat like many other posts discuss with coolant temp issues. Other than that I’ve got a failing temp sensor, or I don’t have an issue at all? From what I can gather from all the threads out there on coolant temps, the DDE is super sensitive on low coolant temps and need to get and stay up in 88-92 range. Whilst my average final temps are fine for avoiding the more serious issues (stuck in warmup modes, glow plug activation <75 and prevention of DPF regen <60), I can’t help think the system is not functioning as intended and causing some inefficiencies. I don’t want this thing to run any hotter, just would like it to be stable as per my 320d. In my mind it’s a fine line between over cooling and running hot, but I’ll take over cooling any day! Re water pump- couldn’t find anything in ISTA. Found a thread with INPA displaying pump speed values, but pump is unlikely to show any codes until it is failed. Also bled the coolant a few times to check if there could’ve been some air bubbles causing the temp drops, but no change.
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03-07-2023, 06:03 AM	#10
ciscorob Private 16 Rep 51 Posts Drives: 2016 BMW X5 sdrive35i Join Date: Jan 2012 Location: Fort Lauderdale, Florida iTrader: (0)	What is the data logging rate? If you're only updating at larger intervals then your values could appear to "swing" because the sample rate is simply updating slower than what is being read. Other than the sampling rate of the data logging you're receiving it could be a sensor that is going nuts and, at least for those of us with an N55, the oil and coolant temp sensors are not only inexpensive, but easy to replace.
	Appreciate 1 RobX52.50 Quote

04-02-2023, 11:54 PM	#11
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	Sampling rate is quite high (somewhere around 3-4hz). Update- I’ve since had water pump replaced as mechanic suspected possible internal damage which may have been inducing air into system (air over sensor resulting in drops?). Also had the EGR deleted and ECU remapped. Turned out the pump had some signs of internal failure, but it didn’t fix the issue. This is an upgraded pump (internals metal vs plastic?). Driving on the highway for over 40mins, the coolant temp never got above 72-74deg. Yet would rise quickly to 88-92 at a stop. As soon I’d accerlerate, again the temps would drop anywhere between 8-12deg C in 3-4seconds. I’m beginning to suspect open thermostat again (it’s brand new and OEM!). At least it’s not as big of job to get to the thermostat now with the EGR and cooler removed. Before then I’ll replace the coolant temp sensor next week.
	Appreciate 0 Quote

04-03-2023, 09:49 PM	#12
Chilled Major 364 Rep 1,019 Posts Drives: F85 X5M Join Date: Sep 2021 Location: Tiny Island, Middle of Nowhere iTrader: (0)	Are you driving this is Sports mode? Because that opens all the thermostats with the intent of lowering all the temps (coolant, oil, etc) The OP of this thread managed to resolve his issue. Not sure if the issue is the same. In his case the temp wasn't coming up high enough.Not swining. https://f15.bimmerpost.com/forums/sh....php?t=1993370
	Appreciate 1 RobX52.50 Quote

05-06-2023, 10:44 PM	#14
RobX5 New Member 3 Rep 10 Posts Drives: 2016 BMW X5 2015 320D Join Date: Feb 2023 Location: Brisbane, AUSTRALIA iTrader: (0)	Solved. Coolant temps back at rock solid 88-92. Thermostat was testing fine on stove. [Symptoms- temp would eventually get to 88 if left at idle, coasting or lots of city driving, but under ANY engine load above 77C, the temp would rapidly plummet 10-15c+ and take a while to get back up again. Any highway driving would cycle 77 max down to 68 repetively] 2 issues - 1/ EGR delete bypass kit. Post this mod, I experience much more severe coolant temp drops. Turns out the egr bypass kit was incorrect for my engine, as it was routing huge amounts of coolant through a bypass hose, likely causing a cooling effect and ultimately bypassing the thermostat in the closed system. Fixed by installing a blanking plate, keeping all coolant in the engine block and warm. 2/original coolant temp fluctuations prior to egr delete which were noticeable (5-6deg) are probably due to air in the system, which is odd considering system was bled multiple times. Additionally, I was also chasing a rough idle during DPF regens (allegedly normal for this engine- which I still doubt). This problem has since gone post EGR delete- there was definitely something up with the EGR. Happy days.
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