{N/A} Regular Unleaded vs. Midgrade?

RyanB

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Is there a real substantive difference as far as engine performance between the two?

Ever since I’ve been driving my GTI, I’ve been putting in mid-grade fuel (89 or 91 octane depending on the station) as I’ve been under the impression that it’s necessary to do so.

Maybe I need to pump 100LL into it to make it REALLY run clean! :)

What’s the crowd say?
 
Have been driving my car for four years on low grade,just noticed the fuel fill says to use high test. Car runs fine on low grade ,with no problems.
 
Is there a real substantive difference as far as engine performance between the two?

Ever since I’ve been driving my GTI, I’ve been putting in mid-grade fuel (89 or 91 octane depending on the station) as I’ve been under the impression that it’s necessary to do so.

Maybe I need to pump 100LL into it to make it REALLY run clean! :)

What’s the crowd say?
I assume you are joking about 100ll running clean. The lead will screw up your Cat.

My owners manual says to run regular (87 octane), but I find it seems to run just a little better and gets just a little better fuel mileage if I run a higher octane gas through it; at least occasionally. It is a small, but noticeable and measurable difference. It also gets about 10% better mileage when I run Shell non-alcohol gas, but the only station that carries it is far enough away that I only buy it when I am on that end of town.
 
Depends if the engine can use it.
For a long time auto engines automatically retard timing to avoid detonation. So if you use a lower octane fuel, and the engine is designed for higher octane, the engine will regard timing and you lose power.
This is why many performance cars require high test fuel. However if you do not hold the pedal to the floor, you likely would never notice.
With that said, we had a Camry which sucked in the mountains when going uphill. Put in high test unleaded and you saw an improvement as you held the pedal to the floor for five minutes...

Otherwise, you are throwing money away.

As always, what does the manufacturer say?

Tim

Sent from my SM-J737T using Tapatalk
 
Our Volvo says to run high octane. After running all three octane's we get better performance and mileage out of the mid grade. Though nothing night and day.
 
Had a 2002 Camry that I was running the 87 in. About a year or so ago it started to run pretty rough... Toyota service guy told me to switch to 89 octane and had no problems since..

My new Toyota (which was built in Indiana) says to use the 87, ran that for a few tanks and then switched to the 89.... runs a lot better.. I wonder if it has to do with all the additives they are putting in the gas in Socialist Republic of Kalifornica
 
If you have a performance engine with higher compression and your manual says run super you better run super! Same with all the newer turbocharged vehicles. I run Super in my C7 Vette and my wifes turbo VW jetta. My old Suburban and Jeep get regular unleaded.
Don't run 100LL in anything fuel injected with a O2 sensor. It will plug the sensor up in no time.
I run 100LL in my golf cart, weedeater and lawnmower because it does not spoil.
 
If your vehicle calls for 87 octane fuel, running anything more is a waste of money. Most modern vehicles that list 91/93 octane as the recommended fuel will run just fine on 87 as long as you avoid heavy-footed acceleration or towing. The ECU will detect knock/detonation and retard the timing (reduce power) to avoid it. That said, if my vehicle calls for 91, I run 91. The $150 it might save me over the course of an entire year by running lower-octane fuel isn't worth it.

On a related note, all 3 of my vehicles are "flex fuel" vehicles as well, but I'd never put a drop of e85 in it. Cheaper fuel that burns more quickly resulting in worse fuel mileage and increased maintenance intervals. I get an honest increase of 1mpg by using e0 vs e10. e85 is just stupidity.
 
My 2000 Forester ran better on Premium No Ethanol. I think it was due to the fact my Evap System was F$%&ed up.
 
Our cars are diesels over here in Europe. Now they are selling an Ultimate Diesel next to the regular. Anyone seen that in the States?
 
What does the OEM say? Burning a higher octane than stated is a waste of money and does nothing for you.
The manufacturer recommends Premium 91, which is what I’ve been running. Either that or whatever the mid-grade rating is (89).
I assume you are joking about 100ll running clean. The lead will screw up your Cat.
You are assuming correctly.
 
The lowest octane fuel you can run without detonation concerns will be the best option for your engine. Higher octane fuels have slower burn rates which turn into less power, less throttle response, etc. The catch is that with higher octane fuels you can make more power because you can run higher compression, more boost, more spark advance, etc.

Your manual will have a recommendation for which fuel to use. Go with that. We end up putting premium in the Benzes because that's what it calls for.
 
Is there a real substantive difference as far as engine performance between the two?

Ever since I’ve been driving my GTI, I’ve been putting in mid-grade fuel (89 or 91 octane depending on the station) as I’ve been under the impression that it’s necessary to do so.

Maybe I need to pump 100LL into it to make it REALLY run clean! :)

What’s the crowd say?
If I recall correctly the 2016 Mk7GTI calls for 87 but the 2016 calls for higher (says so on the fuel door). However, performance testing was always done on 91.

Dyno testing on the Mk6 seems to indicate a 3hp difference at the peak and about 10hp throughout the range.
https://www.edmunds.com/volkswagen/...en-gti-the-effect-of-octane-on-its-power.html
 
My MK7 specifically says 91 octane recommended on the fuel cap.
Sorry, mistyped. I meant that 2015 called for high octane but the 2016 did not.

Bottom line is that it's probably ok and they likely played certification games for power and MPG. But I'd do what the fuel cap says.
 
Volt says high octane so I run 92 in it. The Subaru doesn’t need it so I run 87. Never gotten knocking in the Subaru so I think it’s fine.

In both, I use Lucas Ethanol inhibitor/ cleaner. Not sure it’ll make a difference but I’ve read bad things on the long term effects of Ethanol.
 
Midgrade? Dammit man, you're a pilot! Buy the most expensive fuel you can find.
 
My Beemer 1200RT required high grade but could run on 87 if needed. It had a knock sensor and time retardation function. It kicked in if I ran 87, and the penalty was mileage and power. It did not kick in if I ran 89, and it ran just as well as if I ran 91.

My GSXR 750 required 89, but I ran 87 anyway and it ran great on that.
 
Volt says high octane so I run 92 in it. The Subaru doesn’t need it so I run 87. Never gotten knocking in the Subaru so I think it’s fine.

In both, I use Lucas Ethanol inhibitor/ cleaner. Not sure it’ll make a difference but I’ve read bad things on the long term effects of Ethanol.
Likely great in the Volt since you probably have a tank if gas that lasts a month or more. Subaru, unless you only fill it up every couple of months probably does not matter.

Sent from my SM-J737T using Tapatalk
 
My MK7 specifically says 91 octane recommended on the fuel cap.

What engine? I'd be surprised if it doesn't knock, even on 91. It may not be audible but it is there. You might want to invest in tools to datalog the car and see just how much timing is being pulled.

The Subaru doesn’t need it so I run 87. Never gotten knocking in the Subaru so I think it’s fine.

What kind of Subaru? In the newer cars it seems as though the Subaru strategy is to set their timing tables aggressively and rely on the knock sensor to continuously pull timing for the grade of fuel used. It is probably not a huge deal on a non-turbo car but the turbo subarus, particularly the 2.5L engines, were known for premature failure which I believe is at least partially due to the tuning strategy they employed.
 
Higher octane fuels have slower burn rates which turn into less power, less throttle response, etc.

They don't burn appreciably slower. The octane rating indicates the resistance to detonation, the uncontrolled explosion that causes pressure spikes and engine damage. Higher compression engines are more detonation-prone, but so are are large cylinders, lower RPMs and hotter head temps, all problems in aircraft engines. Higher-octane fuels have a lower energy density, meaning that you don't go quite as far on a gallon, but if your engine needs that fuel to resist detonation you should use it or the ECU will have to retard the timing to stop the knocking caused by cheaper fuels, and there goes your savings. Retarded timing means less power.
http://www.whitfieldoil.com/171.284/vp-racing-fuel-
 
What engine? I'd be surprised if it doesn't knock, even on 91. It may not be audible but it is there. You might want to invest in tools to datalog the car and see just how much timing is being pulled.



What kind of Subaru? In the newer cars it seems as though the Subaru strategy is to set their timing tables aggressively and rely on the knock sensor to continuously pull timing for the grade of fuel used. It is probably not a huge deal on a non-turbo car but the turbo subarus, particularly the 2.5L engines, were known for premature failure which I believe is at least partially due to the tuning strategy they employed.

Forester
 

I was hoping for a model year too...

I reset the ECU in my parent's 2016 Outback with the newer 2.0L FB motor a few months back and you could hear audible knock while the ecu was trying to get a handle on things again. You know it's bad when you can actually hear the knock yourself. I haven't hooked a scanner up to it lately to see how much timing was pulled. It's always running 87 or 89 octane fuel.

My old turbo Subaru and my current turbo Audi both had high(er) compression and are very knock limited. I've pulled a lot of timing out of both cars even though I run the highest octane fuel I can realistically get my hands on.
 
I was hoping for a model year too...

I reset the ECU in my parent's 2016 Outback with the newer 2.0L FB motor a few months back and you could hear audible knock while the ecu was trying to get a handle on things again. You know it's bad when you can actually hear the knock yourself. I haven't hooked a scanner up to it lately to see how much timing was pulled. It's always running 87 or 89 octane fuel.

My old turbo Subaru and my current turbo Audi both had high(er) compression and are very knock limited. I've pulled a lot of timing out of both cars even though I run the highest octane fuel I can realistically get my hands on.

2016 2.5i
 
I was hoping for a model year too...

I reset the ECU in my parent's 2016 Outback with the newer 2.0L FB motor a few months back and you could hear audible knock while the ecu was trying to get a handle on things again. You know it's bad when you can actually hear the knock yourself. I haven't hooked a scanner up to it lately to see how much timing was pulled. It's always running 87 or 89 octane fuel.

My old turbo Subaru and my current turbo Audi both had high(er) compression and are very knock limited. I've pulled a lot of timing out of both cars even though I run the highest octane fuel I can realistically get my hands on.


It just so happens this evening I've been searching the internet for info on this very subject. What hardware/software would a guy need to find for some aftermarket programming on a 2010 2.5 Subaru ECM?
 
Your GTI has a knock sensor, and should run fine on 87, but you'll leave some horses in the barn.
 
Back 35+ years ago we bought a 1981 Buick Skylark (GM X body) with the 2.5 liter 4 banger. In Denver it ran fine on regular unleaded. When we drove it in California, near sea level (and later moved back to California) I had to run the mid-level gas in it to get it to quit pinging. The extra 2 octane points was all it took. Thicker air required slightly higher octane.
 
I run Midgrade in my 2005 BMW X3 and Higrade in the 2016 X3 Turbo. I also look for Top Tier Gas which is more important to me than a few horses if I have to go with a lower grade fuel because of some circumstance.

Cheers
 
Most modern vehicles that list 91/93 octane as the recommended fuel will run just fine on 87 as long as you avoid heavy-footed acceleration or towing. The ECU will detect knock/detonation and retard the timing (reduce power) to avoid it.

The important part of this is the single word "most." A full service place once filled my 92-octane tank with midgrade 89, despite my asking for High Test and a sticker by the cap saying "PREMIUM FUEL ONLY. " Thankfully it was only 6 very flat miles to the auto parts store in eastern Carolina, but she was knocking the whole way, plus another 15 miles or more . . . .

They put those requirements in the Owners Manual, on the gas gage and by the gas cap for a reason.

YMMV, but this is my experience.
 
The important part of this is the single word "most." A full service place once filled my 92-octane tank with midgrade 89, despite my asking for High Test and a sticker by the cap saying "PREMIUM FUEL ONLY. " Thankfully it was only 6 very flat miles to the auto parts store in eastern Carolina, but she was knocking the whole way, plus another 15 miles or more . . . .

They put those requirements in the Owners Manual, on the gas gage and by the gas cap for a reason.

YMMV, but this is my experience.

Yup, that's why I didn't state it in absolutes. When we first got the GXP, the wife was on fumes and got to the fuel station only to find out they were out of 91/93 octane. She called me and asked what to do, so I told her just to add 5 gallons of mid-grade (don't remember if it was 87 or 89) just to get her by for the next day or two until she could stop at another place to fill up with the recommended 91 octane. Told her to be easy with the throttle and acceleration until then.

Now, the one application where I DO use higher than recommended octane is in my boats/jet ski. They typically operate in hot weather, have a lot of full-throttle acceleration runs (skiing/tubing) and cruise at a high load anyway. Also, I believe gasoline will lose octane points over a period of time, so even if the boat sits for a month or two the octane should still be above minimums.
 
You're probably better off running 91/93. Running anything less will probably knock it down to the low octane table
 
Our cars are diesels over here in Europe. Now they are selling an Ultimate Diesel next to the regular. Anyone seen that in the States?
Never seen that, pretty much every place I fuel my pickup is B5 (5% Biodiesel) with some stations where you can get B20(20%) but I fuel up with the trucks. Only 1/3 or so of 'regular' retail stations have any diesel at all.
 
Never seen that, pretty much every place I fuel my pickup is B5 (5% Biodiesel) with some stations where you can get B20(20%) but I fuel up with the trucks. Only 1/3 or so of 'regular' retail stations have any diesel at all.
Over here we are 7% biodiesel. They also have a “truck” diesel. I haven’t researched what the difference is between them.
 
After I wash my hot engine block with cold water I add a few gallons of cold water in with the fuel. I don’t have fuel sumps to drain on the Lexus or the Tundra so I’m sure all is ok. Except cresting that hill sometimes takes awhile.
 
After I wash my hot engine block with cold water I add a few gallons of cold water in with the fuel. I don’t have fuel sumps to drain on the Lexus or the Tundra so I’m sure all is ok. Except cresting that hill sometimes takes awhile.


Water? Maybe some of your Oklahoma friends could set you up with some drip gas, that might work better.

As long as you're cleaning the engine block, don't forget, scalding hot water will clear a frosty windshield in seconds.
 
As long as you're cleaning the engine block, don't forget, scalding hot water will clear a frosty windshield in seconds.

A month or so back, I'm upstairs watching football, the wifey is downstairs checking on a chicken in the oven. I hear a loud bam/crash, followed by language reminiscent of my Navy days. I go downstairs to find the oven door open, the rack out, a glass covered chicken sitting on the rack, oozing goo/chirken juice on the door and floor, and glass shards all about the kitchen. She had noticed the bottom of the pyrex glass pan had gone dry, was worried the chicken would dry out, and so grabbed a glass and filled it with nice filtered cold water from the refrig door.

She poured the water in, then *blamo*! Luckily she wasn't hurt. THAT my dear is called thermal shock, and we do that kind of testing on our parts here at work all the time.
 
A month or so back, I'm upstairs watching football, the wifey is downstairs checking on a chicken in the oven. I hear a loud bam/crash, followed by language reminiscent of my Navy days. I go downstairs to find the oven door open, the rack out, a glass covered chicken sitting on the rack, oozing goo/chirken juice on the door and floor, and glass shards all about the kitchen. She had noticed the bottom of the pyrex glass pan had gone dry, was worried the chicken would dry out, and so grabbed a glass and filled it with nice filtered cold water from the refrig door.

She poured the water in, then *blamo*! Luckily she wasn't hurt. THAT my dear is called thermal shock, and we do that kind of testing on our parts here at work all the time.

Yikes! Glad she wasn’t injured.
 
Is there a real substantive difference as far as engine performance between the two?

Ever since I’ve been driving my GTI, I’ve been putting in mid-grade fuel (89 or 91 octane depending on the station) as I’ve been under the impression that it’s necessary to do so.

Maybe I need to pump 100LL into it to make it REALLY run clean! :)

What’s the crowd say?

91 is "high grade". Use whatever manufacturer recommends. Usually it's 87 or 91, but some do recommend 89

There is no advantage in going higher grade than recommended, there is a disadvantage in going lower grade. In modern car you will lose horsepower and fuel economy(by significant amount), in old car you may get a knock.
 
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