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  #1  
Old 09-25-2016, 07:48 PM
Stevej2001 Stevej2001 is offline
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Poor Mileage-- Thermostat problem?

I've got a '16 328i with 1700 miles on it. It replaced a '14 328i, so the engine is substantially the same. My previous F30 got in the low to mid thirties on the highway. The new one gets in the mid to high 20s on the road. Initially I thought it was because the engine wasn't "broken in."

Today I noticed while taking a 100 mile highway trip the temp gauge stayed quite low, to the left of the mark between 160 and 250, about 200 if one puts numbers on these things. On my previous car the gauge was usually right at or just to the left of straight up (250).

I know the modern BMW temp gauge doesn't tell you much but I'm wondering if this is a problem with the thermostat stuck open and thus with the lower than normal temp. That would cause the computer to provide too rich a mixture.

On the way back the temp gauge was up at about the center but when I left the freeway, it came down quite quickly. In the past my cars have not gone down in temp in this situation.

I'll call the dealer tomorrow but does this sound like a plausible scenario? Or should I just disregard the temp gauge? That still doesn't explain the lower MPG.
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  #2  
Old 09-26-2016, 01:25 PM
Lavalamp425 Lavalamp425 is offline
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The gauge shows engine oil temperature, not coolant. Low oil temp generally indicates you're not pushing the engine hard or it is very cold outside. However since you have concerns about fuel economy and a symptom of low oil temperature in a warm climate after a long drive, a call to the dealer's service department is probably a good idea; "free" maintenance and warranty still in effect and all that.
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Old 09-26-2016, 01:45 PM
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Quote:
Originally Posted by Stevej2001 View Post
does this sound like a plausible scenario?
yes

search for the F30 hidden menu and you can read out the real coolant temperature. that will tell

this for example:
http://f30.bimmerpost.com/forums/sho...d.php?t=677037
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Old 09-26-2016, 02:43 PM
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The car is designed to run cooler under heavy load and hotter under light load. So running on cruise control the highway at a reasonable speed you should be running hotter, then on local roads with a lot of stopping and starting you'd run cooler. I forget the exact range but it's something like 195 - 220F.

Either way, I wouldn't expect there to be a 10 mpg difference.
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Old 09-26-2016, 04:36 PM
Matthew424 Matthew424 is offline
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You car sounds normal to be based on my 2015 F30 (328). I was getting about 29-30mpg when my daily commute was 90% highway cruising. my commute has since changed to more stop/go and is down to about 20mpg. under heavy harder driving conditions in sport mode, the temperature of the car doens't really increase based 230 degrees. dont think i've seen it past 240 degrees ever in the last 14 months (bought car new in July 2015) and that's regardless of driving condition, even when it's 100 degrees outside and AC running full blast.
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Old 09-27-2016, 11:54 AM
LMK5 LMK5 is offline
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Quote:
Originally Posted by Stevej2001 View Post
I've got a '16 328i with 1700 miles on it. It replaced a '14 328i, so the engine is substantially the same. My previous F30 got in the low to mid thirties on the highway. The new one gets in the mid to high 20s on the road. Initially I thought it was because the engine wasn't "broken in."

Today I noticed while taking a 100 mile highway trip the temp gauge stayed quite low, to the left of the mark between 160 and 250, about 200 if one puts numbers on these things. On my previous car the gauge was usually right at or just to the left of straight up (250).

I know the modern BMW temp gauge doesn't tell you much but I'm wondering if this is a problem with the thermostat stuck open and thus with the lower than normal temp. That would cause the computer to provide too rich a mixture.

On the way back the temp gauge was up at about the center but when I left the freeway, it came down quite quickly. In the past my cars have not gone down in temp in this situation.

I'll call the dealer tomorrow but does this sound like a plausible scenario? Or should I just disregard the temp gauge? That still doesn't explain the lower MPG.
Mid to high 20s on the highway is not normal. Based on the erratic gauge behavior, it sounds like a controller issue that may be affecting the fuel system. Are your RPMs what they should be at highway cruise? If so, then it does appear to be an electronic controller issue. The dealer may be able to see if the car threw a code in the past even though no warnings were presented to you by the control display.

BTW, what differences do you see/feel in the drive of your MY16 vs. the MY14?

Last edited by LMK5; 09-27-2016 at 11:57 AM.
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Old 09-27-2016, 11:58 AM
Matthew424 Matthew424 is offline
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How is mid to high 20s on highway not normal???
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Old 09-27-2016, 12:21 PM
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Originally Posted by Matthew424 View Post
How is mid to high 20s on highway not normal???
Because the car is rated at 35MPG highway. Even a leadfoot like me will get 35 or higher per the trip computer when cruising at 70MPH. Achieving the 23MPG around town is a whole other story.
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Old 09-27-2016, 12:37 PM
Matthew424 Matthew424 is offline
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It all depends on how fast you're going on highway. 70mph on i95 or i78 pits you in the right lane on the highway.
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Old 09-27-2016, 12:54 PM
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Like others have said it really depends on the speed you're traveling on the highway and the grade over the entirety of the highway. I don't know exact figures but going 60mph on a 10% uphill grade is going to be similar to going faster (let's say 80mph in this example) on a flat road because either way the engine is compensating for the effects gravity going up a hill. Even if your highway drive is relatively flat the entire way, if you're going 95 mph you shouldn't be expecting great gas mileage. Additionally, if the car is a manual I believe the 6th gear in the manual is geared higher than the automatic so even if you're in top gear in a manual you won't be getting the same mileage as a similar car with the automatic because the RPMs will be higher.
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Old 09-27-2016, 01:05 PM
LMK5 LMK5 is offline
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You're getting away from the OP's issue. He mentioned he's getting mid to high twenties on the highway. It isn't normal, even per his own experience with a MY2014 that he owned. I live in CA just like he does. The nice thing about highway driving is it takes away a lot of variables that are in city driving MPG performance, so you can compare to others' results. If you drive at 70MPH on a reasonably level road you will achieve 35MPH or higher on the trip computer in a 328i. It's very consistent and takes no special technique.
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Old 09-27-2016, 01:16 PM
Matthew424 Matthew424 is offline
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There are too many variables that are not being addressed. Like car speed, acceleration, driving mode of car. In eco pro the car is trying to be as efficient as possible and rpm will sit at 1800 on highway at 70mph. In sport mode car has increased throttle response and will sit st 3k rpm at 70rpm..waiting for you to call for power. Same speed, same road but different MPG results.
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Old 09-27-2016, 01:55 PM
John MS John MS is offline
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Originally Posted by matthew424 View Post
there are too many variables that are not being addressed. Like car speed, acceleration, driving mode of car. In eco pro the car is trying to be as efficient as possible and rpm will sit at 1800 on highway at 70mph. In sport mode car has increased throttle response and will sit st 3k rpm at 70rpm..waiting for you to call for power. Same speed, same road but different mpg results.
+1
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Old 09-27-2016, 04:24 PM
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Poor Mileage-- Thermostat problem?

The real issue is that the op has effectively the same car. It's not like he went out and got an m3, so unless he substantially changed his driving habits, the difference is almost certainly the car. I don't have anything to offer as far as a diagnosis, only to say that something is certainly off. That said, I have always marveled at people who could do better than 25 or 26 combined.
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Old 09-27-2016, 04:28 PM
Kadify Kadify is offline
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The real issue is that the op has effectively the same car. It's not like he went out and got an m3, so unless he substantially changed his driving habits, the difference is almost certainly the car. I don't have anything to offer as far as a diagnosis, only to say that something is certainly off. That said, I have always marveled at people who could do better than 25 or 26 combined.

True. I wouldn't know what could cause a drastic change in mileage between the two cars unless one was an N20 and one was an N26 but considering he lives in CA I'd imagine both are N26.

Ironically, I had a 340i for a few weeks while my car was worked on and I consistently got better mileage than my 428i, it was just 1-2mpg better but still
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Old 09-27-2016, 04:40 PM
LMK5 LMK5 is offline
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Originally Posted by mazdamx594 View Post
The real issue is that the op has effectively the same car. It's not like he went out and got an m3, so unless he substantially changed his driving habits, the difference is almost certainly the car. I don't have anything to offer as far as a diagnosis, only to say that something is certainly off. That said, I have always marveled at people who could do better than 25 or 26 combined.
Finally another person who read the OP's post. Same driver. Same roads. Different car. Low mileage in second car=problem with car.
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Old 09-27-2016, 11:12 PM
Stevej2001 Stevej2001 is offline
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Yes, I'm the OP and I"ve not changed my driving habits. I got one of those OBD plugin things and downoloaded an app and am looking at temp. I've got an appt next week with the dealer.

Someone asked if the RPMs are the same with both cars--yes. This new car has 20" wheels and the old one had 18". Could that effect the mileage. Both are summer tires.
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Old 09-27-2016, 11:26 PM
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This new car has 20" wheels and the old one had 18". Could that effect the mileage. Both are summer tires.
It makes a little difference, not in the range that you are looking for.
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Old 09-28-2016, 12:01 PM
mujjuman mujjuman is offline
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These might be stupid questions, but I just want to make sure and rule them out:

Are you using the same grade of fuel as your previous F30? Premium vs regular? I lose about 2-4mpg in my car if I add regular to an empty tank (Chicago gas prices can get really high during certain weeks, don't judge me )

Check your tire pressures, are they where they should be? I lose another 2-4mpg when my pressures are not optimal.

Is your car packed more with luggage, bags, etc during your trip? I make road trips from Chicago to NY every month, and I noticed that it does add up and make a difference for me.
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Old 09-28-2016, 06:00 PM
Stevej2001 Stevej2001 is offline
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Same premium gas, same luggage/etc.
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Old 10-14-2019, 11:24 AM
Maineiac Maineiac is offline
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Same premium gas, same luggage/etc.
I'm having this same issue, what was the dealer's diagnosis?
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