Synthetic Oil and Gas Mileage

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Mar 22, 2004
Cleveland Ohio
Has anyone ever documented a mileage increase
by using synthetic oil ?? If so on what vehicle
what oil and what was the actual MPG Difference ??
I've been a user of Mobil1 for quite sometime so I've never been able to test that. However, at 100K on my Grand Am GT, I decided to do an Auto-RX cycle even though my engine looked clean. I've been using dino oil for both the clean and rinse cycle like the instructions specified. During this time I've been tracking my gas mileage. When I switch back to synthetic again after the rinse cycle is over we'll see if there's any change in mpg. I don't really think I'll notice too much but it would be nice to see some sort of increase.
Yes, I documented a significant increase in a 1990 Honda that I bought new. With every car since (in the past 15 years) though, I've not been able to see a clear, large difference.
No mpg increase noted in either of my vehicles using synthetic.

In fact, back when I was oil stupid, I ran Super-Tech 5w30 dino in my VW 1.8T; I got 1-2 mpg better gas mileage using that oil than I do using VW approved synthetics.....probably just because ST 5w30 dino is so much thinner than what VW recommends.
Sorry, but I have a hard time believing any synthetic oil would give you that much of an increase. That's a huge difference.

If it's true, then great, but there has to be another factor in there somewhere if your mileage has jumped that much.
True mshu7 but it depends on what harry j had in before.

I had Pennzoil 10w30 dino in my 2.2L Ecotec before I put in Mobil Full Syn EP 5w30 (big difference in weight). I recorded about a 3-4mpg increase.

Then again I lived in Iowa = 99% highway at 55mph.
I'm no expert so I'll accept that it could have been other factors but I think the thickness of oil has a little bit to do with MPG.
I havent seen any change but after one more oil change with amsoil seris 3K im going to try moble one ss or ep and see if there is any difference. Moble oils tend to be alittle thinner so we'll see.
You would need a long term test with the same vehichle.

I did one back in the 80's on a 2.2 turbo MPI in a 85 Daytona. Ran dino for first 10,000 miles. Used CD rated turbo oil 10w-30, castrol vs AMsoil 10w-30 for next 10,000. Some will attribute it to break in but 1st 5000 miles on car matched the 2nd 5000 miles so economy didnt really change.

This was charted with actual miles versus gallons consumed. Gained about 3%. FWIW
"General rule of thumb: 1-3% MPG gain. " Yea thats about right. In the past I have seen truck fleet tests where they replaced all fluids everywhere and the gain was around 3% I believe. But bear in mind they were able to use a lower viscosity fluid in the differentials by going to synthetic.

Being objective you my car owner will not see an increase unless you believe there is one and then you will adjust your criving accordingly. Its just like in the old days when people put "cow magnets" on their gas lines and then realized better millage.
I can't help but wonder if some of these humongous claimed fuel economy increases ocurred with engines still breaking in when the switch to synthetics was made. No accustaions - merely curious. I used Mobil 1 once in a well run-in Ford 351 Cleveland in the early 70's. The fuel useage on a trip to Las Vegas showed a 0.03 mpg increase in economy. Given the price differential, my unbiased, scientific assessment of the promised fuel economy results could be summarized in three words: "Nuts to that!". The rest of that car's life under my tutelage was spent sloshing Pep Boys brand conventional oil around its engine's innards. I traded it in seven years later with 223,000 miles clocked; I was just tired of the car.
No difference in my Corolla(28-30mpg), but about 0.5-1.5 mpg difference in my integra (30-31.5mpg). I would say fresh oil of any kind usually makes more of a difference than synthetic vs. dino.

Fresh cap/rotors and spark plugs makes the most difference for me, from 26-30 on my corolla.
posted 02-24-2006 10:20 AM
Sorry, but I have a hard time believing any synthetic oil would give you that much of an increase. That's a huge difference

It is a huge difference, and I can't tell you how pleased I am! I am sold on synthetics!
From everything I've read Synthetic motor oil has a minimal effect on gas mileage. I'm talking about 2006 not 1980. The quality of the mineral oil has improve dramatically over the last 25 years so the difference is minimal.
Now if you want to talk about replacing your transmission and differential fluids with synthetic oils you will see that 2% to 3% increase in gas mileage. The biggest difference will be in the colder months of the year.
I never really checked the mpg difference between synthetic and dino in my cars.
But after finding BITOG I now run M1 in the motors, Redline in the transmission and differential.
Sure, there's a BIG difference. It reminds me of what I did just this AM. I put a bottle of Techrolene in my tank, then filled it up. The car ran so much better, I almost hurt my neck pulling out of the gas station! Don't tell me the stuff didn't have time to even get through my fuel system, it really works fast!

Actually, I do think some synthetics can yield better fuel efficiency than the same weight mineral oil...but, not very much. It may have to do with the range of viscosity more than whether it is synthetic or not. It SEEMS to me that many synthetics (Mobil 1 especially)are at the thin side of a posted viscosity, where other oils...and German Castrol is an example, and a synthetic example BTW, of being on the thicker side of a posted viscosity. So, my guess would be a 0-30 Mobil 1 (I know they USED to make this oil, I have a bottle of it) would yield slightly better fuel mileage than Havoline 5-30, and GC 0-30 may be the worst of the three for fuel economy.
A year or so ago I switched my 03 Ford Ranger with a 3.0 liter V6 and 03 Subaru Forester with a 2.5 liter 4 cyl. to Mobil 1 and got no mpg increase. Last fall I switched the Forester to Mobil 1 EP and got no mpg increase.
I received no MPG increase when I became educated (BITOG) and changed to GC from Mobil 1
. Engine sure quieted down tho.

But yeah mshu7 - I think one of the biggest factors in my MPG increase was a -0F degree Iowa Winter. 10w30 dino vs 5w30 (thin) synthetic = difference. In 70F degrees? Dunno. +6mpg would sure be nice! hehe
I was getting about 31/38 city/hwy with 93 oct. gas in my '93 Corolla 1.8L using Maxlife Synthetic 10W30. Pretty good, I think, at almost 150k.

When I switched to plain old basic Valvoline 10W30 for an Auto Rx cleaning cycle, it dropped by about 4 mpg. Seems huge, but I've checked and rechecked the math, and it's true. Warm up time is significantly longer right now, which must affect it, although winter in GA is mild, and I've not been running the heater, which makes a huge difference in engine temperature, on the assumption (guess) that higher temperature makes the Auto Rx more effective. I wonder if the Auto Rx itself affects it somewhat?

In about 100 miles I'll switch to Castrol GTX for the rinse phase, and carefully document mpg.

After that, back to synthetics and hopefully mid/upper 30s mpg again. Hoping the Auto Rx also conditioned the seals well (no consumption or loss at all in the cleaning phase), I just placed an order for Redline 10w30. We'll see how that does after 2000 miles of GTX. The weather will be hot again by then, so that will presumably affect things, too. That, more than anything else, seems to affect mpg on this car.
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