How much does oil viscosity actually impact MPG?

[cwilliamsws6]

I have a 2014 Pathfinder Platinum which can run either 0w20 or 5w30. I've always used 5w30 because I've always believed thicker is better.

I just spent $75 on gas and that was filling it from 1/3 tank.

I'm due for an oil change in a couple of weeks and I was contemplating switching back to 0w20 to possibly get slightly better MPG but how much of a difference will it truly make if any?

 

[JavierH19]

Depends on if the oil is heated up. if the engine runs for 20 mins and isn't turbocharged the oil probably never got thinned out but the fuel economy is mostly in the short run time and not so much the long drives. if you're gonna drive for 10 hours there's virtually no difference in mpg between a 0w-16 and 10w-30 since the oil thins out within the hour and the viscosity difference is much narrower than when cold.

But if you splitting 10 hours into 20 mins twice a day you'll get a bigger improvement as the viscosity of the cold oil is thinner so there's less resistance while its warming up. Overall it wont be a huge difference but I'd probably use a 20k rated 0w-20 oil and use it for 15k.

Someone on here posted a 10-11k 0w-20 supertech advanced uoa and it was at 3.6tbn with real low iron. It's a bit close to m1 ep in price but it's an option. No reason to change it in 5k that's also a waste of money.

If i were you id use PP 0w-20 for 10k or a 20k rated 0w-20 and go farther. If your engine doesn't burn and you don't run it hard i don't see how 0w-20 could possibly shorten its practical lifespan.

But it wouldn't be worth it cost wise to put new oil in it again. Unless you can pour it back into the container to reuse in another vehicle soon id just leave it in the sump.

 

[tasch72]

1-2% for each step in grade

So, if you're at 5w-30 and you get 30mpg, you're only going to get 30.5-ish going to xW-20.

 

[CKN]

Not enough you can tell......of course on this board some will admit they can......

 

[ZeeOSix]

Question is ... how much city vs highway driving are you doing? If you were cruising on the interstate on cruise control at a constant speed 80% of the time you might see a difference. All it takes is a couple more fast accelerations around town or a couple of high speed passing events on the highway to kibosh any fuel mileage advantage of a one grade thinner oil.

 

[bullwinkle]

Not enough you can tell......of course on this board some will admit they can......

Not sure, but I bet a car that gets great MPG already (Prius, other 45-50 MPG underpowered econobox) would show a noticeable MPG & power improvement going from (recommended) 0W20 up to 5W30 or higher, at least initially, especially in cold weather conditions. Shear it down some, little fuel dilution, get it hot-bet it's barely noticeable.

 

[tblt44]

Not much.
Tire pressure more important

 

[atikovi]

Not sure, but I bet a car that gets great MPG already (Prius, other 45-50 MPG underpowered econobox) would show a noticeable MPG & power improvement going from (recommended) 0W20 up to 5W30 or higher,

HUH? Why would MPG increase when switching to a thicker oil which increases internal resistance? If that was the case, why isn't the Prius spec'd with 5W30 from the get go? Or 20W50 for that matter?

 

[JohnnyJohnson]

Been tracking this for years with the Toyota Corolla and the Duramax. Even with all the claims in the 18 years I've own the Corolla I have never seen a documentable change in MPG with any oil!

 

[UG_Passat]

When VW went to 508.00/509.00 (0w20) from the usual 40 weight oils, they claimed at least 4% improved fuel economy.

 

[demarpaint]

I wasn't able to measure the "lost" mpg switching both of my Jeeps to xw-30 from xw-20.

 

[PimTac]

Drive more sensibly. Accelerate smoothly. Less lead footing. Keep your tire pressures up.

Drive less. Consolidate trips.

On the fuel line right before the carburetor attach two magnets opposite each other directly on the line. They have to be directly opposite to work. ( Oh wait, that was 1973)

 

[Jackson_Slugger]

Assuming you were using a fully synthetic 5W-30 you probably won't notice much difference in warmer weather. I'd consider running the 5W-30 in summer and 0W-20 in colder months if it makes you feel better....

 

[chainblu]

Didn't we just do this....?

 

[Dinoburner]

Didn't we just do this....?

And often.

 

[mattwithcats]

Look on the sidewall of your tires.

If they read 51 PSI Max, start at 35 and work your way up in 2 PSI steps until they get squirmy.
I have 44 in my rear tires, and 37 up front…

My Dads Cruze runs 44 PSI on all 4 tires…
The fill in his Cruze is Mobil 1 Advanced Fuel Economy, in 0W-30…
Dexos 1 rated…

The fill in my Saturn is Mobil 1 Emission System Protection, in 0W-30,
but that lacks the API sunburst, and Dexos rating…

 

[mattwithcats]

FYI…

Both my Dad’s Cruze and my Saturn run larger tires tham OEM

His were 225/50R17, now are 225/55R17 in “V” speed rating…

My Saturn was 185/65R15, now 205/60R15, in “H” speed rating

 

[OVERKILL]

Look on the sidewall of your tires.

If they read 51 PSI Max, start at 35 and work your way up in 2 PSI steps until they get squirmy.
I have 44 in my rear tires, and 37 up front…

My Dads Cruze runs 44 PSI on all 4 tires…
The fill in his Cruze is Mobil 1 Advanced Fuel Economy, in 0W-30…
Dexos 1 rated…

The fill in my Saturn is Mobil 1 Emission System Protection, in 0W-30,
but that lacks the API sunburst, and Dexos rating…

That is horrible advice.

Tire pressure as dictated by the OEM on the placard is to provide the best balance of predictable handling, braking (stopping distance) and ride. The number on the side of the tire is nothing more than the maximum pressure the carcass is rated for, it has nothing to do with what the tire should be run at. Advocating this approach is reckless, and dangerous.

That's like me telling a guy to just keep adding powder to his cases until his primers just start to pop and then back off. Hey, then when his rifle blows his face off I can be like "hey, must have been on you, it works for me, my face hasn't blown off yet, LOL!".

Good grief.

 

[mattwithcats]

Your stuck on door sticker for a tire size and speed rating that no longer exists on either car…

The OEM tires on the Saturn were 185/65R15 with 30 front / 26 rear, with 35 PSI max, “T“ speed rated…
Current 51 PSI max, 205/60R15, “H” speed rating.
Put 26 in the rear on the current tires, this is reckless, and dangerous.

I do inflate hard for mileage and tire wear, 32f / 40r would be my normal pressure

 

[Gene K]

I have a 2014 Pathfinder Platinum which can run either 0w20 or 5w30. I've always used 5w30 because I've always believed thicker is better.

I just spent $75 on gas and that was filling it from 1/3 tank.

I'm due for an oil change in a couple of weeks and I was contemplating switching back to 0w20 to possibly get slightly better MPG but how much of a difference will it truly make if any?

5W-20 saved about 0.6% over 5W-30 according to Ford. That was approximately 0.12 mpg on a 20 mpg vehicle. 0W-20 would see a much smaller increase over 5W-20 and primarily at very cold temps during warmup. I'm guessing 0 to 0.04 mpg depending on conditions. The bigger gain would come on under 5 mille trips when the oil was at subzero temps when started.