Incredibly good gas mileagle, 04' 5.3liter

Xao · June 2, 2005

Ok, I live in Illinois and I run in between 16 and 18 MPG depending city or highway driving.

My wife and I headed out here to Colorado for family/vacation trip. I average right around 18 - 18.5 driving 75MPH for the drive as usual, but was what REALLY weird, is that I took about 5 days from family and heading out to Moab.

So I filled up here in Denver and headed out for the 6 hour drive through the Mountains. When I got to Moab I refilled and I got 20MPG!!!! That is through the mountains and mostly using third gear since OD doesn't work well in the mountains. This just does not make since to me. I'm also running 85 octane (regular in the highlands) vs. 87 which is the regular back home.

Well I have made my trip back from Moab and the same thing, plus I have noticed I'm getting better gas mileage just around town here. Doesn't make any sense to me!

Can someone shed some light? If running 85 octane is better, I will search high and low to find some. ;) Anyways, I'm just sitting here puzzled, I expected my mileage to really tank, especially with the computer taking time to adjust to the new altitude and all, but it's been a pleasant surprise, hate to give it up!

Thanks!

496 CUBIC INCHES · June 2, 2005

Most engines will get better MPG when they "loosen up" a bit after break-in. How many miles are on your truck.

DougsTJ2 · June 2, 2005

85 Octane is due to the altitude. A poor comparison would be that water boils a lower temperature at that altitude as well.

I have driven several vehicles through the mountains in Colorado. Every one of the has gotten better mileage at higher elevations. My poor explanation would be that the vehicles tend to run on the lean side. There is less oxygen therefore less fuel.

Even if someone can punch holes in this theory...I'm sticken to it.

Shaners · June 2, 2005

I agree with dougtj2. In addition, running in "3" puts the engine in its' power band where it runs more efficiently. Higher RPM's don't necesserily mean worse fuel milage.

Here is an example. Drive your truck in OD on the interstate with no cruise control. Maintain your speed at 65 climbing a hill. Pull the truck down into "3" and leave your foot in the exact same spot, and although your RPM's will increase, so will your speed!!! You will actually have to lighten up on the accelerator to maintain your speed!

JAMIEZ71 · June 2, 2005

When driving from West Virginia to Colorado for a hunting trip this past fall I got extremely good mileage on my truck. I have a bed cover on it and driving thru Kansas I got 22.5 mpg and I averaged about 75mph. Most of the rest of the trip I got about 18-19 mpg. I guess it was a bit lower because of the ways I drove. 80+ mph on average in the other states. On a trip from WV to Darlington race last year I got about 21.5 mpg running 70ish.

pastor scott.com · June 2, 2005

HEY YOU CANT BEAT ME, I DROVE FROM NY TO CA THEN BACK AGIAN.

DROVE THERE WITH ALL STOCK GOT TOPS 18 ON WAY BACK TO NY NOW WITH FLOMASTER AND K AND N DROP IN GOT 22 TOPS.

5.3 O4 BURBAN LOADED WITH 3 KIDS ONE WIFE AND A CAT AND ALL THE GEAR

75MPH

SCOTT

Xao · June 2, 2005

Most engines will get better MPG when they "loosen up" a bit after break-in. How many miles are on your truck.

<{POST_SNAPBACK}>

Well, let's just say I have used this truck.

I have had it for 13 months and I'm sitting on 24k already.

We'll see how it does when we get back home, heading back to Illinois tomorrow night. It will be interesting, but I have to say, I have enjoyed the better gas mileage.

Little Jonny · June 2, 2005

I've got a 2000 Silverado with a 5.3 and last weekend I drove from east oklahoma to central oklahoma averaging 80+ with a few runs to about 120 (no speed limiter thanks to Texas Speed) I averaged 18!

patronus · June 2, 2005

I got 21.3 on a 250 mile round trip on flat land in the same day. Amazing.

2004 Yukon XL 5.3 w/3.73's

mmmikkke · June 2, 2005

A big reason your mileage improves at higher elevations is because the air is thinner, so you have less aerodynamic drag.

And I'm pretty sure that in most major metropolitan areas, gasoline is oxygenated (partially combusted) before you even put it in your tank. The EPA decided to do this to reduce the amount of air pollution caused by old beater vehicles which don't get taken care of. Oxygenation does nothing for a reasonably tuned engine except make it less fuel efficient.

Because oxygenation isn't needed where air pollution is not a problem, fuels in rural areas are not oxygenated. Using "rural" gasoline, you should see some fuel economy improvement because the fuel's not oxygenated.

And finally, if I remember correctly, 84 octane "regular" is available in mile-high Denver, and it performs about the same as 87 octane does near sea level. Using 85 octane fuel, you're moving toward 'mid-grade'... This will let your computer advance the spark just a bit, and so you'll get a bit of mileage improvement here also.