MPG getting worse on Motorhome

Fuel filter has nothing to do with mileage. All it does is filter the dirt out. Injector cleaner might help..There are many things that can cause a decrease in mileage. Quality of the fuel, wind, speed, load, engine wear, tire pressures. The difference you see is probably normal. You will never get the exact same mileage with every tank of fuel. When it drops to a consistent 6-7 mpg then you might have cause for alarm. Just drive it..

B.O.

Hi,

I got a check engine light when my oxygen sensor went out. Changing it improved the mileage, so did changing to 91 octane gas. Fuel injected systems have anti-knock sensors, and low quality fuel will cause the computer to make the fuel mixture rich and/or retard the timing, both will lower the fuel mileage. Perhaps the fuel injector cleaner fools the system to thinking it was higher octane fuel?

Anyway I figure the 91 octane fuel will cost about 5 percent more, but save my by using 10% less gas.

Good luck!

Fred.

PS: THe oxygen sensor is only about $50 and can be installed in your driveway. I used one made for the 96 F-350 with 460" engine, same as my 97 motorhome has. It fits fine, actually there are many vehicles that use that same oxygen sensor. The biggest difference between O2 sensors is the length of the wires and shape of the plug on the end.

Fred.

Replace 02 sensor even if it doesn't trip a code. They get lazy and don't change quickly after a while.

Number one reason is wind, number two reason is wind. on and on. Number 22 reason is wind.

You didn't say that you replaced the spark plug wires. They and the coil can be a source of lower MPG.

I don't see the logic of some of the replies. First the 10 MPG has been consistent over more than 14 years with maybe a plus or minus 0.5 MPG due to change of conditions e.g. speed, wind, hills etc. Second if it were conditions, spark plug wires, 02 sensor, etc-why does it get better when the filter was changed or when injector cleaner is added? I agree that the filter should not change the MPG but it did. DES

I have a theory! I am of the opinion that all the Fuel Gas and Diesel contains fewer BTU 's than it did Five Years ago!

I got 10.5 MPG 5 Years ago now I'm getting 7.5 ! Same Long Trips Fewer MPG and there is No change in My driving Habits or Payload!

VERY bad fuel theses days. Find a good fuel additive and use it all the time. I use SHAFFERS in my everyday car and it is very consistant 2-3mpg better over when i dont use it. It is just a poor quality fuel issue and your onboard computer is puting more fuel in it to run :(

Don't rule out the fuel filter as a cause. Go for a run, then place your hand over your nose and mouth and try to run again. Fuel filter works the same way. The PSI at the pump might be good but drops at the filter starving the injectors.

On my 96 I would change the filter yearly and always would store the gas if over two months with SeaFoam. I could always tell when the injectors would clear up on a cross country trip. It took a few days, but all of a sudden the old gal would pick up her heels.

As a sidebar, V10 came out in 98/99, you said you have a 97 isn't that really a 460 V8?

robatthelake wrote:
I have a theory! I am of the opinion that all the Fuel Gas and Diesel contains fewer BTU 's than it did Five Years ago!!

Gas, yes, diesel not so much. The culprit is called Ethanol.

It doesn't contain nearly as many BTU's as gasoline does.

E15 gasoline only has about 82-85% of the BTU's (amount of potential energy) that gas used to have. If you lose 15% of the available energy! you also lose 15% of the work it will do and so use 15% more fuel to do the same work.

15% of 10 mpg is 1.5 mpg, about what you're losing.

The bump up is the higher energy in the injector cleaner.