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oil change killed gas mileage

cW6mT mKviGTi

Ready to race!
Hello and good day to all. When i had my MK6 GTi i switched from the OEM castrol 5w-40 to mobil 0w-40 @ around 2k miles and noticed my average mpg increase from around 26 ish mpgs to around 28-29 mpgs (mixed city and highway) which increased my full up to full up range about 30 miles.

With my new GLi i switched out the OEM castrol (assuming this is what they still use) 5w-40 to mobil 0w-40 at 1600 miles and my average mpg's went from 30-31 mpgs (before oil change) to about 27-28 mpgs(after oil change) with the same mixed city and highway driving. My range decreased from the average 360's to around 320 ish miles per tank full.

My driving style hasn't changed, i take the same route to and from work, traffic patterns are pretty much the same, no extra warm up times or idling, no new mods, not running the a/c more than before but the outside temp did change from an average of 60's and 70's to 70's and 80's.

The only thing that had me skeptical was the mobil 1 that was used in the gti was the 5 liter jug that i would purchase from advance. The mobil 1 in the gli is from walmart and is about 15 dollars cheaper but instead you get 5 quarts instead of 5 liters (doubt its a made in usa thing vs made in germany since they're both 0w-40's).

When the GLi was new i could get 34-35 mpg's crusing at 65 with no sweat. Now i'm lucky if i get 30 mpg's on the MFD. To my knowledge as the motor breaks in and gets more loose the mpg's would increase as it did in the gti but not in this case. I have OCD with my car's overall performance and this is bugging me. Has anyone else experience anything similar? Thank you for your time.
 
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fredf

Go Kart Champion
1. OP: next time please break up your post with paragraphs and spacing, so it's easier to read.

2. Merkle: M1 0W-40 is an excellent oil and 502 approved. Why wouldn't he use it?

As to the answer, I'm afraid I can't add anything. A lot of people really like M1 0W-40. There are a number of factors in gas mileage and the MFD isn't the most accurate way to check it.
 
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cW6mT mKviGTi

Ready to race!
I use the MFD at a glance while driving but for the most part i usually reset the trip and full up. Then when i refill i take the amount filled and divide it into the amount of miles indicated on trip counter before resetting again for the next cycle.
 

mattdibart

Go Kart Champion
It's the same engine so I'm not sure. Why would you use 0w anyway?

German Castrol is 0w-30 and is excellent oil as well, especially in cold weather.
 

maxtdi

Go Kart Champion
I somehow doubt this is related to engine oil period.
 

Cryptic19111

Go Kart Champion
quit being so anal about it, and just drive the car. switch to something else on the mfd and don't stare at it the whole time you drive. It's not related to the oil, it's most likely that something changed the fuel trims. You could reset those and start over though.

They aren't using GC at the dealer, it's run of the mill 5w40 syntec crap. I don't buy into the whole 502 testing, I think it's a farce. Shell Rotella 5w40 has served me well
 

mattdibart

Go Kart Champion
OP wasn't using GC. He was using 5W-40.

I agree, though, that GC is a better oil.

my post was in reply to Merkle not the OP
 

Skivvy9r

Ready to race!
Hello and good day to all. When i had my MK6 GTi i switched from the OEM castrol 5w-40 to mobil 0w-40 @ around 2k miles and noticed my average mpg increase from around 26 ish mpgs to around 28-29 mpgs (mixed city and highway) which increased my full up to full up range about 30 miles.

With my new GLi i switched out the OEM castrol (assuming this is what they still use) 5w-40 to mobil 0w-40 at 1600 miles and my average mpg's went from 30-31 mpgs (before oil change) to about 27-28 mpgs(after oil change) with the same mixed city and highway driving. My range decreased from the average 360's to around 320 ish miles per tank full.

These are substantial changes in mileage you attribute to engine oil. I've been driving a long time, lots of different vehicles through many oil changes. While I think a quality oil will extend your engine life, I've never experienced any change in mileage due to the oil used. But if you think it's the oil, go with the one your vehicle seems to do best with and move on.
 

SweetJones_29

Ready to race!
I thought this thread was going to be a castrol vs mobil 1 debate.
 

hockeystar17mnj

Ready to race!
The only reason why gas mileage would be affected is if he
1. Used a heavy weight oil like 20w-50 or something like that
or
2. over filled the oil to the point where the crank was completely submerged, aka putting a quart or more over the recommended fill amount
 
could just be your tires' air pressures are lower now? Too many variables.

Maybe the walmart 0w-40 is indeed a little thicker than the Advance 5 liter jug?

Didn't Mobil 1 reformulate their 0w-40 a year ago? Is it still 502 approved?
 
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