-'00 ext.cab XLT
-V8 5.4L triton
-Stock engine (w/K&N filter)
- 265/70 BFG All-Terrains (stock rim)
-about 169k miles
-leaks a little engine oil now & then, but is mechanically sound otherwise.
-low profile toolbox
-I dont drive with a/c on or anything, but my driver-side window is usually down. Maybe my back sliding window too.
-87 octane (prettymuch always)

...Averaging about 8.6 to 9.5 mpg city () and 10.2 to 11.8 hwy ().

I dunno whats going on. I can recall getting upwards of 14-15 mpg hwy when I first got the truck (~74k miles). Ive had the truck for 5 years and it seems like my fuel economy has gotten noticeably worse over the last 10-12 months. And even though Ive been actively monitoring my driving style (trying to counteract this), my efforts are apparently being subjected to the Law of Dimishing Returns.

Bear in mind- Im no leadfoot. If anything, I tend to under-accelerate and just drive slower. (Sometimes i do 5-10 under in the city, when traffic permits). I try to conserve speed as much as i can. I never really go beyond 65mph on the hwy, because my ASE-cert'd buddy says anything above it is probly just wasting gas. Ive been really concerned about this lately, so Ive been doing a good deal of logging and recording trip data. I know its normal for engine mpg to degrade over time, but to me this seems...un-natural? Am I wrong?

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What Im primarily interested in the "Why-is-it-doing-this?" aspect. Like, what (mechanically-speaking) could be causing this? And how much worse could I reasonably expect it to get before I have to do something about it? I went back and checked a number of other previous postings about mpg and such, and while they offer lots of solutions, they didnt quite answer that.

Just To Be Clear: The reason I ask is because im on a college student budget, which is like one step above broke. My fuel economy is obviously bleeding my wallet over time, but I really only drive my truck to and from class & work. I just want to know if this is something I should really correct now or if it can wait.

Thanks.

 

Did you have it tuned up at 100k or 150k? That's a lot of miles lol I would take it to a shop and have them do a standard check up, should cost around $100 for them to go bumper-bumper and do a thorough inspection. Your MAF may need cleaned and sparkplugs replaced.

 

Yeah, sounds like you need a tune up to me. If you have not had this done, then it is time to do it!

 

fuel filter!!!!!!!!!!!!!! also spark plugs, and eigine oil if you haveint done it. im on a college budget also. i did the fuel filter and when the shop took it off i watched black sludge pour out the dirty side. my truck is identical to yours except its a 97 and i get 15.5 on cool sunny days but i run 89 octane. rain makes it go down. so does heat. and red lights. and hills. and road rage. and even though you drive 65 on the interstate, it makes it go down too because of higher crosswinds than through town. so avoid all these things and see how it does. i pay about as much attention to it as you do. maybe more