Miles per tank fading......NEED UR INPUT.

when I picked up my ls it was averaging 17-19 (last sept) depending on how much hwy driving I was doing... I stay on top of the oil, have changed the air filter. every few months I notice it drops a mpg, I'm down to 14 now! 6 months ago I replaced the valve cover gasket, a coil and all the spark plugs. it got better for a week or two, but ended in the 15teens? I haven't touched the fuel filter.. but I am really curious how it keeps getting worse? Oh and I changed the thermostat a little over a month ago. the car is an 00 V8 w/67K, I bought it 13 months ago with 53K... It seems to run good so I don't really get it?
 
02 V8

I stand on it all the time...always did always will.

Get 21-22 average with the stock 17s

19.5-20.5 average with the 20s on.

20s seem to kill about 1.5mpg average.
 
Our Lincoln was getting 15-16 mpg when we bought it used...
Had intake manifold pulled and it was just absolutely clogged with carbon etc... Cleaned it thoroughly and also fuel system for injectors.
I can't recommend it enough... car ran good but now it runs like a top and the avg mpg with ac is about 23 mpg for city- highway its about 26-27mpg no lie. Cheap plugs will cause your heat range to be off. I'd recommend a occasional road trip to blow out the pipes so to speak.
 
Our Lincoln was getting 15-16 mpg when we bought it used...
Had intake manifold pulled and it was just absolutely clogged with carbon etc... Cleaned it thoroughly and also fuel system for injectors.
I can't recommend it enough... car ran good but now it runs like a top and the avg mpg with ac is about 23 mpg for city- highway its about 26-27mpg no lie. Cheap plugs will cause your heat range to be off. I'd recommend a occasional road trip to blow out the pipes so to speak.
What would be the step by step on cleaning out the intake manifold? Thanks!!
 
440 Miles per tank stock 17s. KKM & Torries tune raised it to that from 23.5. %70hwy/30cty moderate driver/sea level.

I think mose fuel mileage problems associated with larger rims is tha fact that (again) the computer is calculating distance by tire revs which are less with larger wheels. For instance Stock 235/50/17 travels 768 revs/mile. I know this is extreme, but a 245/30/22 travels 726 revs per mile. That means that at 60MPH with the stock tire the 22 will read 57.5. This will affect overall vehicle mileage readings!!
 
I never have taken it all the way down to know what my end mileage would be, it never gets under 1/4 of a tank. I do however average 21-22 mpg, sometimes more if I do more highway sales calls. Lately though I have been going to the gym and doing a good bit of city driving, so it is down to 19 and change. I am pretty aggressive though, I have gotten high 26's on the highway doing between 75-80mph. The LS is a beautiful highway car, pretty good fuel mileage at high speeds and what a ride. It sucks your fuel in the city though.
 
I get about 240-268 per tank that sucks... I average about 14.5-23 mpg the lesser the city driving of course.... And I dont push my car at all.
 
I got back last night from a 360 mile trip last night and at most I got up to 26. something on the highway. When I got gas before I left I had around 280 miles till empty and I used sea foam at the same time. I drove the car a bit when I got to where I was going and when I came home I gassed up and got 380 miles till empty but I didn't break a 20. something average.

I wish I knew what the hell the cars problem is cause I don't even think those averages were right seeing on how much gas I had left after arriving at my destination and coming home.
 
I used to get around 15-16 in my 2000 v8. Heavy Chicago driving. It bumped down to 14.8 with my 20's
 

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