When I first bought my truck (see sig) I was getting between 11.5 to 12.5 mpg. Now it has dropped off to 9.5 to 10.5 mpg. I am not towing anything and my driving style has not changed. What gives? What could be some of the reasons for the sudden loss in mileage? I checked the tire pressure, it is where it should be. It has been a little colder than normal too, but does that effect mpg? Thanks you guys!
BTW it has 44000 miles on it.
Tim

 

The cold will kill the mileage...No need to worry!!

 

I am getting 10.5 and i have a lite foot...but here in Utah this time of year we use oxy fuel....its hard on engines and kills your mileage....

Just a thought

 

Its the cold, my PSD has the same problem now that its cold. Just a thought, did you change your fuel filter ever? If not it would not hurt.

 

I asked that question to the mechanics at my wife's company and they told me this: When the engine is cold, it runs in open-loop mode. The computer uses its internal cold-start fuel metering tables instead of relying on the O2 sensors (closed-loop) to tell it to make the fuel mixture leaner or richer. It does that mainly to get the emmissions parts (namely the catalytic converter) to work quicker. The catalytic converter only starts working when the palladium, platinum and rhodium coating on it reach above 200*C. The computer knows that when the engine reaches the temperature where the thermostat starts to open, that most likely the catalytic converter is hot enough. On a cold day, it takes longer to get to that engine temperature and the computer stays in open-loop longer thereby wasting more fuel. On top of that, if the intake air temperature is low, it has to run the mixture very rich because fuel doesn't mist out of the injectors very well when it's cold and therefore doesn't burn well. This is where winter blend gasoline comes in to help. It's reformulated to be more volatile so that is burns better when it's cold. It also evaporates a lot faster while sitting in your tank.
I usually get between 12 and 14 mpg in town and 20 mpg highway in the summer. Now I only get about 10 in town and 16 to 18 highway. This morning, I had to check if someone hadn't glued 2 extra cylinders to my engine.

 

My thanks to all of you! Especially you n578md. Now in light of the temp. issues does using my block heater in any way help? I use it every day.

 

I don't have a block heater on my truck but I think they are the oil heater types on SD's. That mainly helps prevent cold-start wear. The oil gets heated to about 160*F and some of the heat in the oil pan goes up into the upper block so I guess it could reduce the closed-loop cycle a little. It really helps to keep the oil flowing and make the engine a lot easier to crank. (on the starter and battery)
Block heaters are also really helpful if you only drive short trips in cold weather. In weather below 40*F, you have to drive at least 20 minutes for the oil to be hot enough to boil acid and condensation out. If you don't, the acid will eat the metal away and the condensation will rust the inside of the engine. With a block heater, the oil is already at 160*F so even if you only drive 5 minutes, the oil will be at the right temperature to get rid of acid and water.

 

Thanks that helps, cause I only live 6 miles from my work and I never get above 50 mph. And it usually only takes me about 8 minutes to get to work. So I like using the block heater to avoid the cold engine wear at start up. Thanks agian!

Tim

 

I figure you've got the automatic hubs on your truck, but thought I'd throw this out there anyways. I've got the manual hubs and I keep them locked in for the winter. I don't know the numbers but I'm sure there's a mpg loss.

 

Mine has the manual hubs too, and they are in the free position. But I do appreciate your input! And yes there is a loss when they are in lock. Found that out two weeks ago during our snow!

 

I don't know about where you are, but around here they change to a winter blend (or 'green') gas in the winter. Just with that, I drop about 1-1.5 mpg.

 

I am in Western Washington, we usually have very mild winters.
I have never heard of them changing gas mix on us, but I guess anything is possible?!?

 

Actually, it's for "better emissions" around larger cities (ie Philly, etc.).

 

I hear you, the oxy blend absolutely sucks. My truck not only goes down in mileage but runs like crap.

 

I think the pump has to say MTBE on it. Unless you have corn gasohol