gas quality decline?

[johnnyvw]

Has anyone noticed a drop in gas mileage in their cars over the last 3 months? I've noticed my 2020 VW Tiguan has been getting much worse mileage. I know using the a/c has a negative effect, but it's been pretty dramatic. As an experiment, I used premium instead of regular for the trip I took from NC to PA today (just under 10 hours driving, most of the highway was between 65 and 80 mph). The indicated MPG was just under 35, which is pretty much an all-time high for that car. I'm beginning to think the octane is some regular gas is a bit lower than it used to be.

 

[Philpug]

The Yukon has been up, last few tanks were just over 20 MPG

 

[slowrider]

Jeep is around 19.5 mpg. Injector cleaner every few tanks jumped 1 mpg.

 

[Bill Miles]

Has anyone noticed a drop in gas mileage in their cars over the last 3 months? I've noticed my 2020 VW Tiguan has been getting much worse mileage. I know using the a/c has a negative effect, but it's been pretty dramatic. As an experiment, I used premium instead of regular for the trip I took from NC to PA today (just under 10 hours driving, most of the highway was between 65 and 80 mph). The indicated MPG was just under 35, which is pretty much an all-time high for that car. I'm beginning to think the octane is some regular gas is a bit lower than it used to be.

I am not positive on a modern car, but I think inadequate octane would either throw a CEL or result in audible pinging, maybe the PCM retards timing, which I guess could affect mpg.

 

[scott43]

Could be a result of more ethanol in the fuel. Could also be coincidence.

 

[GregK]

The VW Tiguan like most European cars and especially turbocharged ones, are designed to work best with octane 91 AKI/95 RON Fuel. They will work with lesser octanes but they would be more prone to detonation/engine knock. Hot weather and running A/C etc would make this more likely and the engines knock sensor would adjust timing and fuel if this occurs. Would reduce power and fuel economy when this happens and long term can harm the engine.

If you have 93 octane locally as your premium gas, you could mix it with 89 mid grade to get your 91 octane if there’s a big price difference between steps. Won’t be much difference in power and economy between 91 and 93 octane gas on most stock vehicles but a large difference between 87 and 91 especially in summer months.

Another thing that effects fuel economy is the ethanol content in the gas. Pure gas/0% ethanol will have the most energy and best fuel economy with 10% or 15% ethanol blends giving a bit worse fuel economy even at the same octane levels. Rare to find regular gas without some ethanol added but many premium gas options are ethanol free and they are best bet for highest power and fuel economy.

 

[tch]

Interesting original post in that it directly contradicts my own experience. For some reason, I'm getting close to 36 mpg in my VW GTI lately, and I'm pretty surprised.
I don't drive like I'm at the track...but I don't putt-putt along either. I'd gotten used to more like 32-33 in the past.

 

[scott43]

I do find these things kind of dubious. There are a lot of factors at work with gas mileage. However...

 

[Philpug]

I've noticed my 2020 VW Tiguan has been getting much worse mileage ... The indicated MPG was just under 35, which is pretty much an all-time high for that car.

I can barely get 30 with our Alltrack. Be happy with the 35 and be quiet.

 

[Snowfan]

MPG's go lower with ethanol 10%....It is going to increase to 15% with recent stupid gov bill. Corn growing empties aquifers and will become a huge problem along with folks getting lower mpg's at crazy gas and diesel prices.

My new Crosstrek manual gets 33 on hwy and 22 in town. I hoped to be closer to 30 in town but no problem. Short-shifting below 2500rpm's gets mpg's better.

 

[Wilhelmson]

For a while the gas station down the street had crappy gas. If I put it in our cars I noticed a slight difference in performance. But my old lawnmower ran horribly with it.

I never really noticed the ethanol mpg change. Probably depends on the quality of the ingredients, or maybe they are moving up to 15% more quickly than expected. The Ranger didn’t like it.

 

[markojp]

I can barely get 30 with our Alltrack. Be happy with the 35 and be quiet.

I'm 33-34.5 mpg on mine... highway. Record was 38.5 with a raging tail wind.

 

[François Pugh]

I'm falling in with the more ethanol crowd. I noticed about two months ago that one brand where I get points was getting me lower gas mileage, but it's hard to say given so many variables, tailwind/headwind being the biggest factor (other than speed). The correlation was pretty strong with that station though.
Lower octane on a modern car would do it too; the computer compensates for the lower octane, so you don't notice any pinging, just less horsepower.

 

[johnnyvw]

The VW Tiguan like most European cars and especially turbocharged ones, are designed to work best with octane 91 AKI/95 RON Fuel. They will work with lesser octanes but they would be more prone to detonation/engine knock. Hot weather and running A/C etc would make this more likely and the engines knock sensor would adjust timing and fuel if this occurs. Would reduce power and fuel economy when this happens and long term can harm the engine.

If you have 93 octane locally as your premium gas, you could mix it with 89 mid grade to get your 91 octane if there’s a big price difference between steps. Won’t be much difference in power and economy between 91 and 93 octane gas on most stock vehicles but a large difference between 87 and 91 especially in summer months.

Another thing that effects fuel economy is the ethanol content in the gas. Pure gas/0% ethanol will have the most energy and best fuel economy with 10% or 15% ethanol blends giving a bit worse fuel economy even at the same octane levels. Rare to find regular gas without some ethanol added but many premium gas options are ethanol free and they are best bet for highest power and fuel economy.

The original Tiguan did indeed require "premium" fuel. The newer ones (since 2018) do not, probably due to the Budack cycle design

 

[johnnyvw]

As an update, I noticed in my morning commute today that I got an indicated 26 mpg, whereas the past month or so it's been down around 20. It's a very short commute (8 miles) so even on a morning in the mid-60s, the engine isn't fully warmed up until at least half-way there.
My feeling is that although the pump labels say "up to 10%", it probably wasn't near that until recently. And it's interesting that some people have noticed an improvement in gas mileage recently, so that tells me that something is definitely different in the gasoline supply. I am going to continue the experiment for the next few weeks, since my fill ups of premium were in NC and Virginia...just in case the case supply is different than in PA.
Thankfully, I am 3 weeks away from permanently moving from PA to NC, and the current gas prices in the area I am moving to are around $4.30 for regular and $4.65 for premium, as compared to $4.89 for regular in PA.

 

[Bad Bob]

This could be part of the picture. https://nypost.com/2022/04/12/biden-waives-ethanol-rule-as-inflation-hits-four-decade-high/
Sadly, ethanol production is a very high producer of C02. Pay now, pay later.

 

[Seldomski]

Could be a result of more ethanol in the fuel. Could also be coincidence.

Yes, I have this experience when getting gas with vs without ethanol. MPG goes down by about the % of the ethanol... so I am not sure what the point is of blending ethanol into gas?

 

[Bad Bob]

Yes, I have this experience when getting gas with vs without ethanol. MPG goes down by about the % of the ethanol... so I am not sure what the point is of blending ethanol into gas?

Corn farmers love it, and probably the refineries.

 

[GregK]

The original Tiguan did indeed require "premium" fuel. The newer ones (since 2018) do not, probably due to the Budack cycle design

It’s still under a “recommended” not really require as a they are still saying to go with 91 plus octane if possible on every current VW turbo car. They often say you can run regular fuel but don’t highlight the “temporally” which is in place.
The ecu parameters are less aggressive in some models like the Tiguan or TSi Golfs so they will be more tolerant of regular fuel but they will still pull timing etc in high demands.

I’d be alternating mid and premium fill ups to maintain an octane level at least 89 or higher on your Tiguan myself. Would give better performance in all situations and you wouldn’t be overpaying for unneeded octane.

An aftermarket 91 octane ecu tune is more aggressive than a factory one and one should never put fuel below that octane in the car.

 

[GregK]

Ethanol more eco friendly and is good for knock prevention. It’s just not as efficient as pure gas. Cars need modifications if fuel is above that 10-15% level so that’s why that’s the max mixture.