Fuel average after 5W30 oil

[chaudhrysarmad]

I was keep reading on forum that 5w30 is better oil compare to 0w20 factory recommended. I took the chance got Mobil 1 Extended Performance 5w30 and fuel average dropped to 12.5mpg compared to Motul 8100 0W-20 Eco-lite gen3 which was given me 20.0 plus mpg.

car is full stock, any idea what it could goes wrong?

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[CG13]

You’re not dropping 40% of your fuel economy from an oil change. Measure actual miles and how many gallons used. Then compare how you’re driving.

 

[ZackeyTypeR]

I also changed to 5w-30 and have not noticed a large drop in MPGs maybe 1-3 mpg but not that much.

 

[AZCWTypeR]

FYI due to the Iran war the EPA allowed refineries to provide winter blend fuel this summer. This alone accounts for a few percent MPG reduction, then add a bit more for A/C use.

I switched to 5W-30 and noted zero difference in MPG. My driving habits didn't change. I live in a small rural town where horsing around is frowned on, unless you're on a horse.

 

[Ktrw]

I didn't notice ANY difference at all, and I switched back and forth a few times (0W-20 and 5W-30 Pennzoil Ultra Platinum). Stock or tuned, it did not make much of a difference. We're talking like a 2% difference between the two, probably at most. Did you somehow reset the average from your battery getting unplugged and then do some stop-and-go driving or something?

 

[Higgs Boson]

there is no measurable MPG difference between oils. less than .5 MPG, your test is flawed.

 

[ThunderPigeon]

I also saw no noticable difference in MPG switching to 5W30. And don't trust the computer for MPG numbers. Math is the way.

 

[cryptolime]

the only thing i noticed with 5w30 is my knock control would randomly spike at low loads. probably just a coincidence but doesn't happen after switching back to 0w20.

 

[Higgs Boson]

the only thing i noticed with 5w30 is my knock control would randomly spike at low loads. probably just a coincidence but doesn't happen after switching back to 0w20.

Not sure if you meant low loads or low RPMs, but there is oil that controls low speed preignition, if you used a 5-30 that wasnt right for a little turbo motor then you can definitely get some preignition with boost at low RPMs (under 3k or so).

Oil viscosity alone does not make an oil better at controlling LSPI; rather, the specific chemical additive package—specifically lower calcium and higher magnesium detergents meeting the API SP or ILSAC GF-6/GF-7 standards—is what prevents low-speed pre-ignition. [1, 2, 3, 4]

Key Factors in LSPI Control

• • Additive Chemistry: `“Calcium (detergent) increases LSPI events dramatically. Magnesium (detergent) decreases LSPI events dramatically.”, as noted on BobIsTheOilGuy. Modern formulations reduce calcium and substitute alternative detergents.
  • Industry Standards: Always select oils carrying the API SP specification or ILSAC GF-6/GF-7 ratings, which explicitly require passing rigorous LSPI engine tests (such as Sequence IX).
  • Viscosity Role: While some research indicates thinner or lighter oils can slightly influence how much oil film passes by piston rings into the combustion chamber under specific conditions, changing the viscosity grade (e.g., swapping a 5W-30 for a 0W-20) is secondary to using an oil with the correct anti-LSPI chemical formulation specified by your vehicle manufacturer.

 

[alSpeed2k]

I'm running 5w30 LiquiMoly right now and also don't see any noticeable change to my fuel economy

 

[chaudhrysarmad]

I didn't notice ANY difference at all, and I switched back and forth a few times (0W-20 and 5W-30 Pennzoil Ultra Platinum). Stock or tuned, it did not make much of a difference. We're talking like a 2% difference between the two, probably at most. Did you somehow reset the average from your battery getting unplugged and then do some stop-and-go driving or something?

No I didn’t reset and neither disconnect the battery terminals. It’s been over a month since I switched over to 5W30. And average is at continually 12 +/ -

 

[chaudhrysarmad]

I think I have to reset the average and drive on highway speed for couple of hours and keep an eye on it how does it behave. It’s my 6th oil change since 3 years of ownership. I know I have driven it less than 4000 miles total. But one thing I noticed when the car is on normal temp and idling there is noticeable tapping, knocking coming underneath the valve cover. No it’s not high pressure fuel pump, I also owned FK8 for 4 years and pretty familiar with the sound of HPFP. Does the lose valve adjustment from manifold and exhaust side give you bad fuel average? And should I have to talk to dealer because my warranty is going to expire in September?

 

[Ktrw]

I think I have to reset the average and drive on highway speed for couple of hours and keep an eye on it how does it behave. It’s my 6th oil change since 3 years of ownership. I know I have driven it less than 4000 miles total. But one thing I noticed when the car is on normal temp and idling there is noticeable tapping, knocking coming underneath the valve cover. No it’s not high pressure fuel pump, I also owned FK8 for 4 years and pretty familiar with the sound of HPFP. Does the lose valve adjustment from manifold and exhaust side give you bad fuel average? And should I have to talk to dealer because my warranty is going to expire in September?

With that noticeable tapping/knocking noise I would certainly get that checked out. The 5W-30 is not the cause of your problem that is for sure.

 

[WOPSiWOT]

Have you considered taking your foot off the throttle? I only get 12 mpg if I am absolutely hammering it and I've run 5w-30 since the first oil change.

 

[Spart]

I was keep reading on forum that 5w30 is better oil compare to 0w20 factory recommended. I took the chance got Mobil 1 Extended Performance 5w30 and fuel average dropped to 12.5mpg compared to Motul 8100 0W-20 Eco-lite gen3 which was given me 20.0 plus mpg.

car is full stock, any idea what it could goes wrong?

Yeah this didn't happen.

I am running 0W-40 since hitting 800 miles on the car. Below is my MPG log from Fuelly. You'd never be able to figure out where I made the switch if I didn't put a red line on the graph.

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