Crazy(?) Mileage after New Spark Plugs

[ChefJRD]

A few weeks ago I had my 525i aligned and had a (second) new windshield installed, plus I replaced the spark plugs, put in a new water pump (German, Hepu I think, metal impeller), thermostat & alu housing, fog light bulbs and replaced the oil. So I was feeling good after finally getting a lot of things done.

The engine (or is it a motor??) runs smoother with the new plugs and I've noticed MUCH better highway mileage lately. On a few longer trips, I got approx. 28.5 and then 29.5 mpg!!! I had only hit a high of 26 mpg before. In town, however, it looks like I'm still getting 22 or so (and this tankfull seems to be really bad....).

Does this make any sense? Have I just been missing out on good highway mileage with old plugs? Is it normal for city driving to remain low? I forget the exact part number for the plugs, but they were the new version of the Bosch F7 LDCR, something like F7 LDCR+.

[632 Regal]

Im using the new + plugs too, the electrode seems to be a bit thicker. With old plugs it's very possible to have worse mileage.

City driving will always be lower than highway, so yes thats normal.

[ChefJRD]

I expected city driving to stay lower, but the thing is that city mileage hasn't changed, whereas highway mileage increased dramatically. I thought that city mileage would have increased too.

That could be normal, I'm just surprised!

[pyro]

A few weeks ago I had my 525i aligned and had a (second) new windshield installed, plus I replaced the spark plugs, put in a new water pump (German, Hepu I think, metal impeller), thermostat & alu housing, fog light bulbs and replaced the oil. So I was feeling good after finally getting a lot of things done.

The engine (or is it a motor??) runs smoother with the new plugs and I've noticed MUCH better highway mileage lately. On a few longer trips, I got approx. 28.5 and then 29.5 mpg!!! I had only hit a high of 26 mpg before. In town, however, it looks like I'm still getting 22 or so (and this tankfull seems to be really bad....).

Does this make any sense? Have I just been missing out on good highway mileage with old plugs? Is it normal for city driving to remain low? I forget the exact part number for the plugs, but they were the new version of the Bosch F7 LDCR, something like F7 LDCR+.

I would be hella happy with 22mpg city i only get 15-16... But then again i Have m50 non vanos

[Akhil]

here in Houston I can get as low as 11 MPG to as high as 20 MPG depenging on what time of the day it is. Man this Houston traffic really sucks.

[SRR2]

Take good fuel usage data over the next ten fillups, THEN get excited about any increase in mileage. I have detailed data on cars I've owned for the last 20+ years. One thing that I can count on is unexplained temporary short term increases/decreases in usage. One tank (or five) does not make a trend.

In order of significance, the biggest identifiable contributors to statistically significant mileage changes are:
1. Major change in usage pattern i.e. more/less highway miles
2. Ambient temperature
3. Change from heavy dino oil to synthetic -- this was in older cars
4. Change to low rolling resistance tires (Mich Energy MXV4)

[Scott C]

A few weeks ago I had my 525i aligned and had a (second) new windshield installed, plus I replaced the spark plugs, put in a new water pump (German, Hepu I think, metal impeller), thermostat & alu housing, fog light bulbs and replaced the oil. So I was feeling good after finally getting a lot of things done.

The engine (or is it a motor??) runs smoother with the new plugs and I've noticed MUCH better highway mileage lately. On a few longer trips, I got approx. 28.5 and then 29.5 mpg!!! I had only hit a high of 26 mpg before. In town, however, it looks like I'm still getting 22 or so (and this tankfull seems to be really bad....).

Does this make any sense? Have I just been missing out on good highway mileage with old plugs? Is it normal for city driving to remain low? I forget the exact part number for the plugs, but they were the new version of the Bosch F7 LDCR, something like F7 LDCR+.

I don't think your range is that different from what I see - 21 (mixed city/hwy) and 30 +/- on flat highway at 70MPH indicated, which really means about 65 MPH.

Scott

[Akhil]

Take good fuel usage data over the next ten fillups, THEN get excited about any increase in mileage. I have detailed data on cars I've owned for the last 20+ years. One thing that I can count on is unexplained temporary short term increases/decreases in usage. One tank (or five) does not make a trend.

In order of significance, the biggest identifiable contributors to statistically significant mileage changes are:
1. Major change in usage pattern i.e. more/less highway miles
2. Ambient temperature
3. Change from heavy dino oil to synthetic -- this was in older cars
4. Change to low rolling resistance tires (Mich Energy MXV4)

SRR2,

Does low rolling tires tires increase or decrease milage? My car had 225/50R16 tire since I bought it. I also had a vaccum leak from not-return value until 2 weeks ago, which I fix. That added up about 3 MPG to milage.

Thanks
Akhil

[SRR2]

Ideally you'd want the least rolling resistance possible. The problem is finding out how to buy such a tire. The manufacturers refuse to disclose the data. The best data I know of came from Consumer Reports who did a comprehensive test on it a few years ago. The differences in losses was pretty dramatic. Rolling losses add up to increased heat, wear, and fuel consumption.

[Akhil]

Ideally you'd want the least rolling resistance possible. The problem is finding out how to buy such a tire. The manufacturers refuse to disclose the data. The best data I know of came from Consumer Reports who did a comprehensive test on it a few years ago. The differences in losses was pretty dramatic. Rolling losses add up to increased heat, wear, and fuel consumption.

has any rule of thumb that increase of some numbers (from 2 numbers in tire size) will increase or decrease the it rolling resistance?

thanks
Akhil