10mpg Sucks, Don't You Think?

strafingmoose · March 17, 2008

Hi guys!

So both my latest calculations indicate that my truck has been doing 10 MPG.

I think it's a little abusively low. That gas mileage is more the one for a 2500HD 6.0 if you ask me.

Tires are inflated at 35 PSI. No tonneau cover or fiberglass bed cab either. It's winter over here, not too cold too, but I figured I should be able to do at least 13-14 MPG.

What should I look into ?

Thanks.

bassadict69 · March 17, 2008

How many miles on truck? If quite a few miles you may try replacing your O2 sensors.

I have the 4.8 also in a regular cab 4x4 & was getting about 13.5 mpg before my tune.

99silverado1500 · March 17, 2008

Ive been averaging 10 city 12 highway lately in my 5.3 i dont understand whats going on. I can get 13-14 in the summer on city.

strafingmoose · March 17, 2008

How many miles on truck? If quite a few miles you may try replacing your O2 sensors.

I have the 4.8 also in a regular cab 4x4 & was getting about 13.5 mpg before my tune.

About 65k miles on. O2 sensor ? That's quite a pricy part isn't it ?

strafingmoose · March 17, 2008

Ive been averaging 10 city 12 highway lately in my 5.3 i dont understand whats going on. I can get 13-14 in the summer on city.

Your situation is perfectly normal if it's winter in your area. 3-4 MPG drops because of the cold is very common I heard.

HawkScot · March 17, 2008

Winter is tough on mileage, we like to warm up before we drive, we run in 4WD more, we run the fan on high more, run seat heaters, more headlight time (less daylight), etc. Our wintertime mileage is usually 1-2mpg less than spring-fall.

Lincoln30 · March 17, 2008

How old are your plugs and wires??? The 100K mile OE plugs don't really make it 100K miles in my experience.

Fuel filter???

Griffin86 · March 17, 2008

I heard that the O2 sensors have been going in gm trucks. My friend had to replace his 02 sensor in his truck because it was burning a 1/4 tank per hour (5.3l). . When he tried to order one for $150 they were all sold out a various places, he had to go to the dealership and pay $215. I just bought O2 simulators for my truck for $80 so i should be all good.

redvett · March 17, 2008

I heard that the O2 sensors have been going in gm trucks. My friend had to replace his 02 sensor in his truck because it was burning a 1/4 tank per hour (5.3l). . When he tried to order one for $150 they were all sold out a various places, he had to go to the dealership and pay $215. I just bought O2 simulators for my truck for $80 so i should be all good.

The simulators only set a value so the PCM is happy, but the fuel correction needed for best performance & mileage isnt there. To get the best performance & economy you need working O2's.

Griffin86 · March 17, 2008

I only did the rear 02s i took my cats off. My gas milage substantually improved after that

Griffin86 · March 17, 2008

I thought that the front ones measure the a/f and make the changes and the rear ones monitor to see if the cats are working. This is on my '99.

Volucris · March 17, 2008

I think you have something wrong. I just used my truck to drive up to the mountains and back - 17.3 mpg, all hiway but going up and down some pretty steep hills, averaging around 65. That's with a 4.8, 373 gears, 4WD, crew cab. 85 octane gas too.

This was also from calculating it out, I don't have a mpg indicator in my truck.

redvett · March 17, 2008

I only did the rear 02s i took my cats off. My gas milage substantually improved after that

The reason you fuel mileage improved is you removed the cat's that were bad. Thats illegal and to sell it that way is too. You could be fined. Its a federal offense. If the buyer decides to press the issue after he finds out your in trouble.