Fuel Consumption

[Big Blue Ram]

I have a 2001 Dodge Ram 1500 4x4 Quad Cab with the 5.2L 318 5 speed. I've installed a Jet powerchip, K&N filtercharger system,under drive power pulley, 160 low temp thermostat, and free flow exhaust. I was running stock 31 x 10.5 tires and I was getting around 300 miles per tank (about 12 mpg). I then put 33 x 12.5 Micket Thompson Baja Claws and the mileage went to 240 per tank (about 9-10 mpg). What happened? Did the tires alone do this? I've also noticed that my exhaust tips are very black? Is not all of the fuel being burned? Any help is appreciated.

Thanks,
Jason F.

[Dirty Dog]

By increasing tire size, you've done two things that adversely affect mileage. You've increasde the amount of weight that the engine has to spin, and you've changed your effective final gear ratio (that's why your speedo and odo are off too). You can get some of it back by re-gearing, but the extra weight is still goign to be there.
Poor mileage goes with a built truck, especially with the smaller engine.

[v10sport]

Also the tires throw off the speedo. Your truck is really traveling 1 mile but it only registers .8 mile. You need to condsider this when calculating fuel mileage.

[sgbofav]

The 160 thermostat is bad for your mileage. A 180 T-stat is much better. The bigger tires also increase your wind drag which decreases mileage. The higher your truck is off the ground, the greater the drag.

Bill,

[Biginuf]

You mentioned the exhaust being black, does it blow anything black out of the exhaust? if so the plenum gasket may be bad. If its bad that would also hurt your gas milage.