Oil Change and Gas mileage

[mie634]

My girlfriend swears after 3000 miles on an oil change her gas mileage drops by 3-5 miles a gallon then goes back up with fresh oil. I say it has to do with her driving habits and warming up her car when it is cold. Anyone have any idea if she could be right about this? She has a 2001 Nissan Altima and runs 5W-30 dino oil.

[ May 20, 2004, 04:14 PM: Message edited by: mie634 ]

 

[Vuarra]

Sounds more like a case of the dino shearing out of it's weight. Fuel dilution may have something to do with it as well.

She may want to go with some longer drives to burn off the fuel in the oil, or go with synth.

Vuarra

 

[Schmoe]

Hey, a new guy answering a new guy, that's cool and welcome to the forum. This place is like....everything you wanted to know about oil but were afraid to ask. Anyway, my take on that would be about what V said....but in this case the oil would be thickening up which would rule out fuel dilution. It's hard to believe 3-5 mpg decrease but it could happen. Take a sample of the oil to be sure.

 

[Vuarra]

quote:

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Hey, a new guy answering a new guy, that's cool and welcome to the forum.

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I've been lurking for about 6 months, enough time to be sold on GC in my SBC Buick Regal. So far, after about 6 000 km, I've had to add I bottle GC (but I know about my cyl head leak).

And BTW, **** Walmart Canada for going to only Fram products

 

[Virtuoso]

Thing is, wouldn't you get better milage with the thinner, sheared oil?

 

[jthorner]

quote:

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My girlfriend swears after 3000 miles on an oil change her gas mileage drops by 3-5 miles a gallon then goes back up with fresh oil.

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I would bet her something serious that a controlled experiment would disprove her theory.

I've been driving and changing oil for 25 years now and always check fuel economy with each fill up. Across many different vehicles I've never seen fuel economy improvements simply from an oil change with a short OCI and the same oil used pre and post change.

John

 

[wulimaster]

I would guess that the oil she is using contains friction modifiers which are used to get the petroleum oil to surpass the synthetic reference oil fuel economy for a GF-3 rating. These last long enough for the test period but after a short while in the car they go away and the fuel economy gains also go away.

I know that the newer sequence VI-B test uses roller lifters and doesn't respond to the friction modifiers like the lighter viscocity oils but my guess is the formulators of these oils still formulate them with friction modifiers for the sequence VI test so that they can be used as factory fill in new cars. I would have to look up CAFE rules about oil used for their testing and oils put into new cars having to be comparable with respect to fuel economy figures derived from the CAFE testing, but I would suspect that is the reason for new oils to still contain friction modifiers even though they don't have much of an effect under the new sequence VI-B test.

For those who don't think synthetics get better fuel economy than dinos, why do you suppose the GF-3 designation uses a synthetic for a reference oil?

jthorner - Careful what you wager.

[ May 20, 2004, 11:49 PM: Message edited by: wulimaster ]

 

[mie634]

Thanks for everyone's help on this. I am looking at the Schaeffer's brand of oil for her next oil change. If I can spend more than a few weeks at home maybe I can figure this car out.

 

[TomJones76]

There's no way you can get 4 MPG out of an oil change. I think going from one grade to another is good for 3%, tops, and I'm imagining that Altima gets in the vicinity of 30 MPG.
Maybe her oil changes coincide with trips to visit her old college buddy 3 states away, and skew her statistics or something?

 

[Mark in NY]

For those who don't think synthetics get better fuel economy than dinos, why do you suppose the GF-3 designation uses a synthetic for a reference oil?

jthorner - Careful what you wager.

[/QB][/QUOTE]

Mike,

You saying going to Mobil-1 0-20 might show an MPG improvement from Motorcraft 5-20?

 

[Bamaro]

IMO, there is no reason for this. Unless she has docomentation on this I would guess it is her imagination.

 

[wulimaster]

quote:

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Originally posted by Mark in NY:

For those who don't think synthetics get better fuel economy than dinos, why do you suppose the GF-3 designation uses a synthetic for a reference oil?

jthorner - Careful what you wager.

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Mike,

You saying going to Mobil-1 0-20 might show an MPG improvement from Motorcraft 5-20? [/QB][/QUOTE]

Maybe, maybe not. Motorcraft is a synthetic blend.