12, really?

[litebulblsc]

I just bought a 2000 Silverado 1500 with the 4.8l. Ran my first tank of gas through it and crunched the numbers to see that it only gets 12 miles to the gallon? 85% of my driving was expressway.

So any one have any ideas of what I can do to improve it? I would like to get it to 15mpg which shouldn't be asking to much I think.

Thanks,
Josh

[gregory5000]

It sounds like there is something wrong with your truck. My 2001 4.8 with 140k miles gets 18 MPG on a bad day. The best I have gotten is 24. The average is 20. What RPM's are you turning at 55? I am turning 1500 rpm's with a 3.23 rear ratio and mine is 2wd.

[litebulblsc]

I am not sure on engine RPMs. I should mention that I drive 75-80 MPH depending on the traffic.

[1990SSchevy65]

Ummm...you definitely have something going on. I have a 2003 CCSB 4x4 with a 6.0, 3.73 rear end and get 12-14mpg, but I only drive about 5 over. Driving that much over the limit does get you to places faster, but you are running higher RPMs which will eat up more gas to run the truck.

[gregory5000]

I just got back from a road trip to the smokey mountains. I filled up at home, drove 200 miles at 70-80 on the interstate and then drove 150 miles in town at the area cities. That 150 miles was 3 days of mountain and stop and go traffic. I got 19 on that tank.

[Warrens69GMC]

need more info: 2wd/4wd, what "extras" are you carrying (tools, equipment, passengers) and is there a lift on the truck? What size tires?

[GCncsuHD]

Sounds like something is wrong for sure. Do you have a SES light on? Make sure it isn't just a light burned out also, it should come on when you turn the switch on before cranking. A common failure is the knock sensors get wet and corrode, resulting in the engine going into limp mode making it retard the timing severely which can kill the fuel mileage and power. Bad o2 sensors can cause it to run rich also killing fuel mileage, or clogged cats.

Originally Posted by litebulblsc

I am not sure on engine RPMs. I should mention that I drive 75-80 MPH depending on the traffic.

That definitely doesn't help your mileage as mileage starts dropping off fast above 65, but still it shouldn't be getting 12.

[biggsteve97]

I have a 2002 Silverado 1/2ton 4x4 with the 4.8L and even with a full tool box (approximately 150lbs) Stock I got 18-19 hwy roughly 14-15 city. With the dynomax Ultra-flo exhaust, throttle body spacer, and cold air kit I now get 16-17 city and 21-23 hwy. I have seen as high as 25 hwy but have not been able to duplicate more than once.
my 03 Z71 Tahoe stock was 11 city 16 hwy now with the headers, Dynomax kit, cold air kit, throttle body spacer I get 15-16 city and 21-23 hwy. combined I average 18 mpg most tanks now where stock was a mere 13.5mpg combined.

[litebulblsc]

I know driving that fast will lower my mpg. That is why I would be happy with around 15mpg. Lift is still sitting in the house, tires are stock, it is 4x4, automatic, extended cab, short bed.
One day I had two passengers the other 3 I was alone. Just carry a small 1/4'' drive tool set so maybe 10lbs there. SES light works and is never on. Tires are inflated to 35psig.

It needs shocks, but that shouldn't hurt my mileage...

I am unsure of the rear axle gearing too

[Lee H]

The number one cause for reduced mileage (not including driver) is O2 sensor. Sounds like its time to change it/them out.
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[crazy longhorn]

My 02 silverado (extended ,2wd), is consistant @ 13.7 in town/18-19 on the hyway. This is also a 4.8, with 162,000 rounds on the clock. On the hyway, I run 70-72(seems to be the sweet spot), & the old gal is bone stock....albut a 14" body Magnaflow added to the stock system. I have noticed however , when running 78-82 mph, the mileage sucks crazyL

[litebulblsc]

Does anyone besides magnaflow make a replacement y-pipe? Mine is all beat up and probably wouldn't hurt to replace the cats.

[67ChevyRedneck]

Yeah, something definitely wrong, my 5.3L 4x4 has never gotten below 13mpg in winter with 100% city driving (unless I needed to use 4x4 which is rare down here). Towing my boat drops it to 11, but unloaded it's normally 14 around town and 17.5-18 on the highway @ ~ 70. I've been told that cats and o2 sensors will always throw a code on these trucks if they're bad, but I can't verify that 100%, but considering there are 2 cats and 4 O2 sensers (at least on the 5.3 there is, I'm assuming hte 4.8 is the same) I think I'd have someone check it out first.

I would try a full tank of "slowing down" to 70 if you can. Also, if your doing a lot of high speed weaving/passing dropping it down to 3rd will eat fuel mileage too. Might be something to try before throwing $ at it.

[litebulblsc]

I hold a constant 80 so it is always in overdrive. This tank is seeming better, but it is hard to tell for sure because of the sketchy gas gauge. I poured some Lucas fuel cleaner in it just in case it actually does something. Got my leveling kit on it yesterday along with new shocks. Drives a lot better now.

[litebulblsc]

Up to 14.4 mpg on the second tank

[Dustin07]

yeah I was getting 20+ on my 99 4.8L ext cab 1500. always a min of 18, well over 20-23 on hwy driving.