I personally have never noticed a measurable difference in MPG using different oil viscosties, but I was curious if anyone else has. My examples are small four cylinder economy cars so maybe that's my issue. My son's 2012 Corolla has used 0w20 all the way up to 10w30 high mileage oil and the MPG's seem the same. My current 2024 Corolla came with 0w8 and currently has 0w30 Mobil ESP, I'm averaging about 42 MPG highway on the 30wt oil.
Difference in MPG using different oil viscosities?
- Thread starter Corollaman
- Start date
I've never seen any real difference. Run100% synthetic and tried different brands and weights but i fill up at different stations which how the level both directions and the pump shut off will vary. Keep track of the mileage using trip odometer and auto fill shutoff gallons. Very rural closest town is 18 miles, road 55 mph and very hilly. 95% of my driving Missouri ozarks.
Gas mileage will depend on gas quality way more than oil viscosity.
Never
Going from a 5W-30 to a 15W-50, just for grins, did make for a reduction in fuel economy in the two Accords I tried this with years ago, but it was in the range of maybe 3-4%, so nothing you'd really notice unless you logged fuel mileage on every tank, as I did and do.
And tire pressure.
There's a real difference. You may not notice it because your driving style is too inconsistent but there's a difference. The difference adds up when you're talking hundreds of thousands of vehicles.
Can you post a photo of your huge garage?
Blenders and manufacturers have stated it’s about a 1% to maximum 2% difference between grades. Well into the noise of everyday driving. Your change between a 20-grade and a 30-grade is this amount. The winter rating doesn’t really play into it, only the operating viscosity.
This is the key point. Automakers are rated across their entire fleet (i.e. all the vehicles they build). If they get 0.2 or 0.3 better MPG per vehicle - you and I won't "see" this - extrapolate this across the hundreds of thousands of units they build, it is where it counts. This is why the discussion about EPA and CAFE factor in when thinner oils keep being spec'd but only in the US.
I have used 0w30, 5w30, and 10w30 in my old avalanche and an old matrix. No difference that I can tell
The different blends of fuel (summer-winter) matters more to MPG than oil viscosity. Simply airing up your tires to the allowed max, not rodding your car, and combining trips when possible is way, way, way more impactful to fuel consumption than viscosity. Way more.
Went from 0W-20 to a 5W-30 in my baby Duramax. Couldn't see any difference.
I seem to get between 0.25-0.40 MPG less using a 5w-40 vs a 5w-30 but there were some variables that took place so not for certain. Let's say I get 0.25 miles per gallon less, 20 MPG, & $2.50 gallon average. Over 100k miles that would be $3,125 more dollars.
You almost have to wonder why CAFE exists since this is reducing state & federal gas tax revenues. It also reduces oil company revenues and costs many industries potential jobs. In a way, it’s government picking winners & losers, rather than letting the market decide. Consumers as a whole give the market much better direction than government, based on their buying habits.
If people wanted only 50mpg cars, trucks wouldn’t have been the best selling vehicle class for the past 40 years…
If people wanted only 50mpg cars, trucks wouldn’t have been the best selling vehicle class for the past 40 years…
Patman
Staff member
I can always tell the exact moment when I’m getting the summer blend of gas because it’s worth an honest to goodness 10% improvement in my Civic!
Yep. I played with 5w40, 20w50 and 5w30 over 10 years and saw a measurable difference in all 3. Over a couple of hundred tanks it was statistically significant enough to be measurable but not enough to worry about. I ditched the spreadsheet when I sold the car a couple of years ago, but somewhere in the ball park of a 5% difference between the 30 and the 50. Between 30 and 40 there was a trend but nothing much to write home about. The 50 was a cheap conventional while the 30 & 40 were synths so it wasn't a straight shootout.
My truck with no changes has gone from about 19.3 on winter blend and is up to 20.7 and climbing. That’s over about 6k miles without a reset, so short term is obviously even higher. Probably close to 10% overall…
Just give every vehicle a temperature-controlled inline fuel heater (like on-demand electric water heater in your house) at about 120*F that shuts off once ambient is above 60*, and run summer blend all year. Seems like it would work?
This^. It’s a very small number of mpg increase. But the EPA is looking at millions of autos and thinks even the smallest increase is beneficial. I can say that I get 1-2% better mileage with 0w-20 than 5w-30 in my Honda Fit. Not much at all. But in the totality….it probably makes sense.
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