My once great mpg has dropped. Not huge but about 1-1.5mpg. Truck runs normal and recently passed a dyno smog check. Now i did get new tires, but they are the same size as the old ones. I went with the Bfg all terian, instead of a more high way type. Is the tire enough to cause this? And what should i look for? Oil and filters are pretty new. I have heard about the up pipes but dont really know what to look for? Any thoughts on the simple stuff to check will be helpfull. Joe

 

are they switching to winter blend diesel in your area? I usually lose 1 to 2 with winter blend fuel.

 

I am having the same issue. I think it's my up pipes. A while back, like maybe 6 months ago, I had a tiny wisp of soot showing on the passenger side up pipe. I wasn't too concerned, and my mileage and power were still great. Then suddenly my mileage dropped.

I crawled under there with a brigt flashlight and sure enough there was now soot all the way around the donut on the pass side. Plus, climbing up into the engine bay looking down around the tranny dipstick, all black with soot. Also, I can hear the leak ticking away.

So I have ordered bellowed up pipes, new engine boots, and while I am in there I am going to install an FRX. Just finished building a top side creeper to make pulling the turbo easier.

 

thanks. I first noticed this quite a while back. So thinking back on it, it is probably the tires. It is not winter blend fuel yet here. But still want to look at all easy to check stuff. I am a electrician, maintence guy. So i try to keep up on filters,fluids etc. But i only have a very basic understanding of the diesel. So do the tubeing with the clamps that are around the turbo a thing to check? Is one brand of oil better for mpg? I have used the Motocraft or the Mobil delevac. Also, i dont really understand what to look at with the up pipes.
Sorry for my ignorance. I am a long time Ford guy. I have had my Truck for 8 years now and it has been pretty trouble free. Joe

 

There can be a lot of things that can cause that. Driving habits and the like. But I think the tires are the key there. More knobby tires=more rubber on the road=less fuel mileage. As mentioned before, the type of fuel your local stations has can change mileage as well. Try running an additive through your tank to clean things out a bit. It helped me a ton a while back.

 

Keep and eye on it and if it keeps dropping your air temp sensor in the spider may be going bad.

 

Tires that are worn or have low tread depth get better fuel mileage than new one's.

 

Im with everyone else, tires.....The compounds are alot different from the a/t's to the hiway tires.

 

Do you have any links on how to check that, or what if you just unplugged it?

 

Here's a pic from a Van for illustration of an up-pipe leak.

Pic courtesy of Dan (Kwikkordead)

The black soot streaks on the left up-pipe are evidence of an exhaust leak.



Here the top of my up-pipe was solid black.

 

Well it is a cheap part, like 20 bucks, so if you're concerned you could just swap it out but from what I remember you should be able to check it with the AE tool. It should give you the air temp and if the engine is cold and if you pull the sensor out so it is exposed to the outside temps it should read what the outside temps are.

 

Thanks for all the input. I will keep an eye on it and make sure it doesnt drop again. Will run some additive thru it and do some experiment with buying fuel at different places. Hunting season is coming up so i have a lot of driving the same. It will give me a chance to monitor the mpg in repeat trips. Will look for leaks etc. Joe