synthetic vs earth oil MPG

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Jan 31, 2004
I drive a 1998 C2500 Chevy Suburban back and forth to work and a few times a month tow a 28' TAG trailer with my race car. If I had the bucks I'd have a tow truck and a go to work ride.

I have used a 10W-30 Dino oil from day on and have 180,000 miles .
I change it around 5k based on UOA testing at Blackstone labs. TBN is pretty much depleted at 5k. Used Chevron and now use Shell Formula. I get my oil at Costco. I drive very easy maybe 65 on the turnpike and slow to accelerate in an effort for best MPG. 42 gal tank at 2.81/ is $120 ouch.

Anyway I get 15mpg back and forth to work and have seen as good as 18 on almost pure interstate driving. It's like 10 or 11 when I tow.

Here's the question.

Costco sells a 10W-30 and 5W-30 Mobil 1 synthetic oil. It's $27 for 6 qt's. Is it a given that I will see better mpg with that oil? An if so how much 2%, 5% 10% or more???

I'm assuming I could stretch the interval to 10k min.???

The synthetic engine oil will give you a minimum increase in fuel economy. The biggest gain will come from replacing the transmission and differential fluid with synthetic. As far as using synthetic in the crankcase the benefit is lower operating oil temperature, extended oil change intervals, and a cleaner engine internally. In the past the difference between synthetic and mineral oil was pretty significant.
In the last 10 years or so the quality and the additive packages in mineral oils have cut dramatically into the fuel economy difference between the two types of oil.
Increase your tire pressures by 2 to 3 psi over the manufacture recommended level. That should help some as far as highway mileage goes.
At least you live in a relatively flat area.
For me changing the oil at 5000 miles is a minor deal. I have a house with garage and this takes maybe 30min max. No jack needed.
At 2% the $'s does not pan out the way I see it. 180k miles and still runs fine I thinks it's happy in the mech area. I'm paying about $7.50/ change now, not including filters. The syn at X2 interval would be close to 2X the cost pe change, considering the intervals. Just made a quick calc and the delta using the 15mpg is 16 gal or $45/ year. Maybe at $2.80/ it does work out...if 2% is good for my lead sled...Thanks

ALS how much has neen documented (improved MPG) on BOAT's like this
with Syn ATF and Rear oil? I have Amsoil in the rear now.

[ April 15, 2006, 08:04 PM: Message edited by: quick_16 ]
I don't know about bigger rigs, like yours. And, I don't know about the differential/transmission effects. But, I do know I've gotten better and better mpg on my Subaru when I went to synthetic oil, another increase on synthetic transmission, and another increase on synthetic differential. However, this could ALL be due to being "broken in" more fully. Only have 15,000 on it now. But, getting up to 35.xx mpg highway with a car rated at 28 hwy. Heck, I get almost 28 in town!
My Silverado (4.8l V8) has run Mobil 1 for a few OCI and other Conventional oils in it's 43k miles and the best overall MPG has been with Pennzoil 5w-30 and Chevron 5w-30.

My last 4 tanks with Chevron (the .49 cent oil) has been 21.43 mpg. (this is over 1500 miles)

Not too bad for a 5,000 4x4 ext cab truck driven around town and to work (90% hwy)

With my truck, there was NO increase of MPG with Syn.


Anyway I get 15mpg back and forth to work and have seen as good as 18 on almost pure interstate driving.

Thats great for a 3/4 ton!

I had a 3/4 ton f250 with a 360 V8 and it was good for 10 mpg... Loaded or empty.

Thankfully gas was a little cheaper back then..

Take care, Bill
I have noticed that synthetics give noticeably better mileage, but much more so when there is some factor like a tail wind. Was in my 2005 Corolla, drove from NM to AR in one day, with a 40 mph tail wind, Amsoil 10w30 w/ Ea filter and ATF.

Got 46 mpg on that one tank, and some nice views of some grass fires. This was around New Years day 2006. This car was loaded with all kinds of luggage and I was going about 80 the whole time. The best part is that the oil is still golden beautiful after 12,000 miles.
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