X5D started getting 5mpg worse

Spyro235 · 01-11-2019, 08:04 AM

All- last night my mileage took a turn for the worse- 22.8 mpg at 68mph, rather than the expected 29. Just earlier in the day I was averaging 27 at 75 mph. I started monitoring the coolant temp,m and I was only seeing 60C, while fully warmed up at idle/ running on the highway. This is during the second half of an hour long drive. I never monitored temps before I saw the MPG drop, but do I just assume my thermostat has failed open? The car's in the shop for the a wheel bearing, and I'm considering having them just do the thermostat while it's there. Any opinions?

M5_1of400 · 01-11-2019, 08:32 AM

Quote:

Originally Posted by Spyro235

All- last night my mileage took a turn for the worse- 22.8 mpg at 68mph, rather than the expected 29. Just earlier in the day I was averaging 27 at 75 mph. I started monitoring the coolant temp,m and I was only seeing 60C, while fully warmed up at idle/ running on the highway. This is during the second half of an hour long drive. I never monitored temps before I saw the MPG drop, but do I just assume my thermostat has failed open? The car's in the shop for the a wheel bearing, and I'm considering having them just do the thermostat while it's there. Any opinions?

100% change the Tsat.. 60C is really low temps.. it should be in around 88-90C.

Spyro235 · 01-11-2019, 08:36 AM

Quote:

Originally Posted by DieselDemonDM

100% change the Tsat.. 60C is really low temps.. it should be in around 88-90C.

I figured- thanks for the quick responses demon. I'm super, super well versed in the n54, because I've been modding that platform for 2 years now, but the m57 is my first diesel, and I feel a bit out of my depth. Just don't want to mess anything expensive up while I save up for the deletes!

kbsilver · 01-11-2019, 08:37 AM

I seem to lose about 2% MPG for every 10 deg drop in outside temperature. Also decreasing MPG is one of the few symptoms of CBU, until it gets real bad and sets off the SES.

Spyro235 · 01-11-2019, 12:53 PM

Noteworthy- it was like 15-25 F out last night when this happened. Still seems really low.

rbreding · 01-11-2019, 07:44 PM

A therm is about 40 bucks or so and a gallon of coolant on hand. Cheap fix. Be aware that some terms are either bad off the bat or fail prematurely. So get one with a warranty.

01-11-2019, 08:04 AM	#1
Spyro235 Captain 260 Rep 714 Posts Drives: '10 X5D, '04 330i ZHP Join Date: Jan 2017 Location: CO iTrader: (0)	X5D started getting 5mpg worse All- last night my mileage took a turn for the worse- 22.8 mpg at 68mph, rather than the expected 29. Just earlier in the day I was averaging 27 at 75 mph. I started monitoring the coolant temp,m and I was only seeing 60C, while fully warmed up at idle/ running on the highway. This is during the second half of an hour long drive. I never monitored temps before I saw the MPG drop, but do I just assume my thermostat has failed open? The car's in the shop for the a wheel bearing, and I'm considering having them just do the thermostat while it's there. Any opinions? __________________ Daily/ Tow: 2010 X5 35D - 326k, Deleted w/DUDMD Stage 2, Sutphin Trans tune, Comfort seat retrofit Fun car: 2004 ZHP 6mt - 256k miles, z4m FCAB, stock. Drift car: 2001 330i for sale
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01-11-2019, 08:37 AM	#4
kbsilver Captain 142 Rep 634 Posts Drives: 340GT & '22 eDrive40 Join Date: Jan 2012 Location: North Jersey iTrader: (0)	I seem to lose about 2% MPG for every 10 deg drop in outside temperature. Also decreasing MPG is one of the few symptoms of CBU, until it gets real bad and sets off the SES.
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01-11-2019, 12:53 PM	#5
Spyro235 Captain 260 Rep 714 Posts Drives: '10 X5D, '04 330i ZHP Join Date: Jan 2017 Location: CO iTrader: (0)	Noteworthy- it was like 15-25 F out last night when this happened. Still seems really low. __________________ Daily/ Tow: 2010 X5 35D - 326k, Deleted w/DUDMD Stage 2, Sutphin Trans tune, Comfort seat retrofit Fun car: 2004 ZHP 6mt - 256k miles, z4m FCAB, stock. Drift car: 2001 330i for sale
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01-11-2019, 07:44 PM	#6
rbreding Second Lieutenant 54 Rep 238 Posts Drives: 328d, 335d, x5d Join Date: Sep 2016 Location: OKC iTrader: (0)	A therm is about 40 bucks or so and a gallon of coolant on hand. Cheap fix. Be aware that some terms are either bad off the bat or fail prematurely. So get one with a warranty.
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