Longer OCI and MPG?

[icruse]

I used the search engine to no avail, so alas, here I am.
If one is using longer oci (longer than the 3,000 mile) say between 5000 and 10,000 (or maybe a litle more mileage)
1) If the mpg stays pretty much the same throughout does this mean that the oil is staying within its rated grade?
2) If the mpg begins to noticebly (3 or 4 mpg and all driving variables are the same as first oil) drop around 4,000 miles after oil change would that be an indication that the oil is going out of grade, i.e. thickening up, and has lesser abilities as the one that is holding up with a consistent mpg?
Just a thought that came across my mind.

Good Day,
Steven

 

[rpn453]

I don't think oil would ever go far enough out of grade for you to notice a fuel economy difference, unless it has been in there long enough to become a sludge-pit.

 

[OriginHacker21]

I ran some Castrol Syntec for 7,000 miles for the first time ever and I didn't notice a MPG difference. I keep sharp records with a ScanGuage and mileage count upon gas fillup. But, my head (probably) was telling me the engine wasn't sounding/feeling as smooth in comparison to new oil.

 

[icruse]

Thanks for the input rpn453 and OriginHacker21.
I looked up the Scan Gauge you mentioned, intersting, I was not aware of this neat instrument.

Good Day,
Steven

 

[Matt_S]

The answer to both questions is maybe or maybe not. With regard to gas mileage, some engines show more sensitivity to differences in oil viscosity than others. You can't really make any assumptions unless you've tracked your MPG over a variety of viscosities and mapped the results. Even then, differences in oil brands can come into play, too.

IMHO, if you see a difference in MPG toward the end of an OCI, it could be due to a lot of factors, not just viscosity differences.

 

[The Critic]

I know of many people who claim that their cars "lost smoothness" and loss some fuel efficiency after 3-4K on the same oil fill. NOLN had a recent article about this, but they didn't state the exact reasons why.

I understand that many oils on the market today have added friction modifiers for fuel efficiency, so it may be that these friction modifiers are wearing out after the first few thousand miles?

 

[OriginHacker21]

That would be my guess The Critic - sorry but no facts behind that one other than: I've never run an oil past 5,000 miles before. During 7,000 mile run of castrol I could swear the engine felt and sounded rougher - especially at idle.

I'm assuming that the older the oil gets the more dirt, grit, contaiminents it holds hence the darker color. Could that be the cause of a slightly rougher feeling/sound? Obviously an oil filter is supposed to catch the big stuff but the really small dirt would circulate - virgin oil would be the smoothest because it doesn't have any of the "small" dirt in it. So whenever someone changes their oil - their engine would be smooth'er than the 5,000 mile oil - technically... Makes sense to me - anyone feel free to correct.

 

[GoHeels1981]

I am a 5w-20 fan...run it in all of my vehicles. I do notice that I get better mileage 2-3% on the back side of the oil changes....I assume it is due to shearing.

JMHO.

 

[lindermant]

Like OH21 I use a scangauge, and I keep a gas log spreadsheet tracking data at each fillup. Using Havoline 5W-20 dino in my 05 Civic (non-hybrid):

47.33 MPG tank avg at ~7400 miles into current 10K OCI
48.53 MPG tank avg at ~7900 miles into current 10K OCI

Of note, these two tank averages were the highest I've recorded since purchasing the car. No loss in MPG from this end with longer OCI's...

 

[LarryL]

Give me a break. Getting stuck in traffic a couple of times will make a bigger difference than dirty oil. If you want to feel better about doing something to get better mileage, air your tires up to 40psi and pin a note on your dashboard to remind yourself to keep off the brake pedal.

 

[surfstar]

I know 5k isn't a long OCI for most people (although it is for some), I couldn't detect any difference when looking at the MPG data.
MPG vs miles on oil

It looks as though the graph links are down (or are now blocked by my co.), but the data is still there.

 

[jmacmaster]

I'm on my second 10,000 mi. run of Mobil 1 in an 03 Ford Ranger and my wife's near the end of a second 10,000 mi. run of Mobil 1 EP in an 03 Subaru Forester. During all the time that the Mobil has been in both vehicles the mpg has been the same. Ranger consistently gets 20-21 mpg and Forester consistently gets 26-27 mpg.

 

[TomJones76]

I did a 10K OCI recently, my oil thinned noticeably, and I could tell an MPG difference despite using a Scangauge and calculating per-fill mileage using my Palm Pilot too.