Fuel

[Mervkirwin]

I just purchased a 2017 GMC Sierra SLT All Terrain with the 6.2 L , I see in the manual it states to use 93 Octane in the truck for better fuel mileage and performance. Does anyone know if this is true and have you noticed better gas mileage.

 

 

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[Justin101714]

GM will always suggest to use top tier fuels no matter what. In my 5.3 I've only ever run 87-89 and it runs fine. MPG average on the DIC shows 29.1

 

 

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[Black02Silverado]

I stick to what the manufacture suggests myself. As stated above, using Top Tier fuel is the way to go.

[SouthernSilveradoGuy85]

If I remember right, I have read where some 6.2 owners accidentally put in regular 87 or equivalent and the engine didn't seem to run right. The 6.2 is tuned to run on premium so that's what you should run. Sure it will run on a lower octane if you're in a pinch, but I wouldn't recommend it and just stick with premium. I also never use any mom and pop store to fill up. Always a top tier brand or just well a known brand.

[kstruckcountry]

91 and up is fine, doesn't have to be 93.

[Supreme Pizza]

As you already know: The octane scale is the opposite of what most people think. The higher the octane, the lower the combustibility. So low octane fuels can produce more power (theoretically). Why do we put high octane fuel in race cars and high performance engines? High performance engines need to have less volatile fuel to keep the engine from exploding. Some of the fastest cars on earth run on alcohol, which is obviously less explosive than gasoline. Running too low of octane could be looked at like this: Your running a fuel that is too powerful for your engine. The volatile fuel will detonate too early, and cause random explosions inside your engine. Your engine tries to compensate for the unplanned explosions by retarding the timing. You want your engine to run in its ideal environment, so that it will be efficient and last as long as it can. Save pennies at the pump to destroy your engine. If you really want to use cheap gas, just "cut" it with something to lower the octane. When we raced bikes competitively, all the well known national guys ran a mix of pump fuel and airplane fuel. The airplane fuel was very high octane. What ever your rig calls for, use that.

[Brianskeet]

High octane top tier fuel is cheap insurance to keep your motor happy. The timing is adjusted on the fly by the engines computer and higher octane allows for more timing advance. Timing advance adds power and efficiency, but only up to the point where the engine can tolerate it.

[gone_fishing]

If I had a 6.2, I wouldn't run anything less then 91 octane. With my ScanGauge monitoring timing and KR (knock retard), I have witnessed first had the affects of lower octane on my 5.3. I try use at least 89 and will occasionally use 91 if the price is right. Since the 6.2 has a higher compression (11.5:1 vs 11:1) using anything less then 91 will most likely result in KR and timing be retarded (aka loss of power).

[ram1067]

GM will always suggest to use top tier fuels no matter what. In my 5.3 I've only ever run 87-89 and it runs fine. MPG average on the DIC shows 29.1

 

 

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29.1......i haven't seen that good on my yet. You must be keeping it below 30mph all the time....

[txab]

29.1......i haven't seen that good on my yet. You must be keeping it below 30mph all the time....

Maybe he's using km.

[Spurshot]

As you already know: The octane scale is the opposite of what most people think. The higher the octane, the lower the combustibility. So low octane fuels can produce more power (theoretically). Why do we put high octane fuel in race cars and high performance engines? High performance engines need to have less volatile fuel to keep the engine from exploding. Some of the fastest cars on earth run on alcohol, which is obviously less explosive than gasoline. Running too low of octane could be looked at like this: Your running a fuel that is too powerful for your engine. The volatile fuel will detonate too early, and cause random explosions inside your engine. Your engine tries to compensate for the unplanned explosions by retarding the timing. You want your engine to run in its ideal environment, so that it will be efficient and last as long as it can. Save pennies at the pump to destroy your engine. If you really want to use cheap gas, just "cut" it with something to lower the octane. When we raced bikes competitively, all the well known national guys ran a mix of pump fuel and airplane fuel. The airplane fuel was very high octane. What ever your rig calls for, use that.

 

Mostly agree. However, it was recently pointed out to me that all the gasoline has the same specific energy (BTU, joules, etc). The "octane" ratings are now controlled with primarily anti-knock additives. A reference was cited and I did read a article supporting that. But there was a time that high octane was lower specific energy fuel

[tnchevy]

I have also ran into this because in my spare time I like to fix up old 2 stroke street bikes. Back in the 60's and early 70's these bikes ran on regular pump gas but the octane reading back then is much higher in reality than what it is today. To counter this I mix non-ethanol 93 with 100 octane racing fuel (the racing fuel has ethanol so I don't like to run it straight). On my more modern motorcycle (large air cooled V-Twin) I run the lowest octane gas I can get away with (bike requires 91 or higher octane) which means 87 in the winter, 89 in the spring and fall, and 93 in the heat of summer.

[Black02Silverado]

If I had a 6.2, I wouldn't run anything less then 91 octane. With my ScanGauge monitoring timing and KR (knock retard), I have witnessed first had the affects of lower octane on my 5.3. I try use at least 89 and will occasionally use 91 if the price is right. Since the 6.2 has a higher compression (11.5:1 vs 11:1) using anything less then 91 will most likely result in KR and timing be retarded (aka loss of power).

Black Bear Performance informed me to run at least 89 in our 5.3 even if it wasn't tuned. They said these new engines benefit from higher octane and running anything lower isn't recommended by them from what they are seeing when tuning the 5.3 and 6.2.

[VdellaV]

I have a 5.3, and live in Mexico, we only have 87 and 91.

 

I wouldn't dare putting Mexican 87 on my truck,

 

I hate the fact that I can only have Pemex fuel. Damn Socialism

 

All hail free market

[Motor City Rick]

Octane usage is based on compression ratios and timing curves. 5.3 liter can use 87 octane because of it's compression ratio of 9.5 to 1, whereas a 6.2 liter (L86) runs 11.5 to 1 compression ratio. That is why the manufacturer recommends higher octane fuel.

 

Another little factoid, the 10% ethanol blends are great for cold winter start ups but recommended in very hot Arizona weather.