This Just In... All 2008's must run PREMIUM!

[mikejr]

Originally Posted by Hummer Guy

Alright, I looked a little further and found a "facts and myths" bulletin on fuel/additives for ALL 2008 and prior GM cars and trucks:

This is straight from the bulletin:
? Use the Recommended Grade (Octane) Fuel

Purchasing higher than required octane fuel is a waste of money. Using higher octane fuels in a vehicle that only required regular unleaded fuel will neither increase performance nor improve gas mileage. In all cases refer to your owners manual and ONLY use the octane rated fuel recommended for your vehicle.

Important: In high performance GM vehicles that DO require Premium (91 octane or higher) fuel, you MUST use fuels of at least this octane. Use of lower octane fuel may result in reduced performance, knocking, and/or permanent engine damage not covered under the terms of the New Vehicle Warranty.

This is straight from the 08 manual:

Use premium unleaded gasoline with a posted octane rating of 91 or higher. You can also use regular unleaded gasoline rated at 87 octane or higher, but your vehicle's acceleration could be slightly reduced, and you might notice a slight audible knocking noise, commonly referred to as spark knock. If the octane is less than 87, you might notice a heavy knocking noise when you drive. If this occurs, use a gasoline rated at 87 octane or higher as soon as possible. Otherwise, you could damage the engine. If you are using gasoline rated at 87 octane or higher and you hear heavy knocking, the engine needs service.

_________________________________

So, I read the owners manual as 87 octane is acceptable for use. I've driven a ton of 08s on regular octane and never heard any knocking. The bulletin talks about vehicles that "Require premium" and the manual says "You can also use regular unleaded gasoline rated at 87 octane."

The high performance cars I've seen that run on higher octane say "Always use premium fuel, below 91 octane may damage engine components bla bla bla"

87 Octane is fine in 2008 H2s and H3s - has anyone here heard knocking?

No i've had no knocks, but the engine does idle a bit rough. But I just figured it was how the engine was supposed to idle. Almost like it has a hypo cam in it or something.

[Alan06SUT]

I bet mid grade would work fine.

[Hummer Guy]

Originally Posted by mikejr

No i've had no knocks, but the engine does idle a bit rough. But I just figured it was how the engine was supposed to idle. Almost like it has a hypo cam in it or something.

I don't think higher octane would smooth the idle, but I agree that 2008 models idle a little rougher. The exhaust, to me, sounds a lot better too (more aggressive), and that's just one of the 'downsides' to having the bigger, nearly 400 HP engine in the '08

[mikejr]

Originally Posted by Hummer Guy

I don't think higher octane would smooth the idle, but I agree that 2008 models idle a little rougher. The exhaust, to me, sounds a lot better too (more aggressive), and that's just one of the 'downsides' to having the bigger, nearly 400 HP engine in the '08

I remember when they bumped up the HP in the avalanch from 2003 to 2004 it idled rougher too.

I agree with you, that exhaust sounds AWESOME....thats probably why I am only getting 10.7 MPG, I keep putting my foot into it to hear that rumble. It is sweet sounding.

Mike

[BigBlue]

Originally Posted by mikejr

I remember when they bumped up the HP in the avalanch from 2003 to 2004 it idled rougher too.

I agree with you, that exhaust sounds AWESOME....thats probably why I am only getting 10.7 MPG, I keep putting my foot into it to hear that rumble. It is sweet sounding.

Mike

Yeah, that new rumble is definately worth the extra .20 a gallon.

[frenzy1]

I'M DRUNK

[Agriv8r]

[H2 007]

Have the same slight rough idle at times as others have mentioned. Have been using Shell 87 since day one. Just filled up today and got 13.6 MPG, city driving, with 1050 miles on it.

On the highway, if I set the cruise to 65MPH, I can get a solid 16 - 17 MPG. Driving around rural roads at 40-45MPH and I have seen 18+ MPG.

Of course this is all with very conservative driving.

No knocks, pings or anything else for that matter.

Overall, I think this new engine / trans / gearing is great.