After a string of very bad junk cars that kept dying on me, I got a 2001 dodge ram v6 magnum regular cab, automatic truck back in the middle of the summer and wanted to wait awhile until posting to confirm my bad MPG, but, sadly, I can only get maybe 130 miles in a tank till the halfway marker...that's only 10mpg (26 gallon tank...so...130 divided by 13 since that's halfway)

the truck has no misfire, cranks right up everytime, I'm thinking maybe it's the tire pressure being off? They're all bridgestone 17inch tires on it, but only at 31psi...the door frame says 41...they're all used tires so I'm not sure if they're the exact same model, the front passenger even looks like it's an offroad type bridgestone since the tire tread pattern is much different than the others, but I know for sure one tire in the front said 44 max psi.

I know using bigger tires than stock from reading will slightly throw off the odometer and even speedometer, but by how much?

The check engine light is on, for a small and large evap leak, but when I did some reading before people claimed they've had that code for many years with no ill effects, from what I what it just claimed that's an emissions code since the fuel vapor isn't getting recycled...I did buy a new gas cap to try and fix the code but the light hasn't gone away, maybe I should manually clear it.


truck only has a little over 153,000 miles on it, not very many considering the extreme high mileage vehicles in my area considering its age. Maybe o2 sensors coming into play as well? I do a mix of city/highway driving, roughly 50-50 I'd guess....sadly lately I've gone out of my way to not even drive the thing around due to the poor mileage...I don't even run AC at all (it doesn't work...). Since the truck has no misfire I haven't personally pulled the plugs, but I'd assume since it drives fine they'd be ok. The previous owner said he had a recent tuneup done, so that would be about 4 months ago now. The air filter is the cheap fram one but it looks fresh so I believed him on the tuneup story.


I thought about getting the ~20 dollar spectre drop in air filter (apparently K&N sued them back in 2011 and apparently manufactures their stuff now...-shrug-) but...many people online claimed the K&N filter actually made their MPG worse INSTEAD of increasing it like so many claims it does, so I didn't want to buy the cheaper Spectre air filter and it just make my MPG worse. I have read getting a dual exhaust plus K&N/Spectre air filter is supposed to increase MPG, but by how much exactly I've honestly never gotten a scientific answer online from people.

it's just really upsetting to have a 6 cylinder vehicle eating your wallet up in gas mileage. The fuel economy gov website said I'm supposed to get 14 in the city and 18 highway, and I can't even get that...but yet I hear online all the time about guy's v8 trucks getting 20+ MPG or at least way better than my puny 10mpg, that's something I'd expect out of the old chevy 2500 gas guzzler big block 454 engine I got rid of years ago, not a 6 cylinder 3.9L ram.

I know not to expect the world of a smaller engine pushing a full sized truck, but, I'm getting quite a bit less than the advertised stock MPG specs which is my problem. I get less MPG than bigger engines running their AC get.

sorry if that was a bit much to read, I just wanted to try and give as much info as I could. I also did a recent oil change.

 

I would check the vac lines going to the evap canisters on the passenger side. You could have a major vac leak.

 

First, you need to accurately calculate your fuel mileage. The gas gauge is in no way a 'real' indicator of how much gas is in the tank. When mine reads E, there is actually six gallons still in there.

What size are the tires on your truck, and what size did it come with stock? (build sheet will tell you, the door sticker lies. )

 

Thx for the help, I watched a youtube video showing where to check for the large/small evap codes I have, it's apparently a common fault for the hoses on some canisters under the truck to develop big holes in them.

Stock was 16inch tires I believe, mine has 17 inch. I don't think 1 extra inch would throw off the readings much, but maybe.

I filled it up completely about 2 weeks ago and have driven it sparingly due to the bad mileage, how could I tell exactly how much gas is in the tank? Drive until the low fuel light comes on and record how much I got? I filled it up when it was a little above the halfway point and it took 24something to fill up, gas was 2 a gallon here, so a little over 12 gallons, pretty close to being spot on since the tank is 26 gallons total and I wasn't exactly on the halfway marker to begin with.

Maybe a vacuum leak is the likely cause indeed, I don't think spending money on tune up items would fix it, as I have no driveability problems, or misfire or anything. I know having tires a little lower than "normal" is a few percents lower mpg, but not this much. I also read before of studies comparing driving with the tires a little low vs filling them to the sidewall maximum and the difference was very small and they said it wasn't worth the ride being horrible and jarring due to the tires being so stiff. Airing them up to 35psi each wouldn't hurt I suppose, heard that's what most tire places air truck tires up to.

 

Fill up your tank, note current mileage. Drive it for a few days. Fill up the tank again, note how many gallons it takes, see how many miles you have driven since the last fillup, and do the math. That will give you a fairly close idea of gas mileage.

What size are the tires? (original, vs, what size is on there now.) That information can make a major difference. If your originals were 245/75/16, and your current tires are 315/7017, that's a big jump in size. We need that information, to even hazard a guess.

 

Maybe it depends on my driving patterns this month, or maybe it has to do with fixing a bad wheel bearing and servicing the transmission before I filled up this last time, but I'm currently at 148 miles since last fillup and there's still about 1 and a half lines till the halfway marker. Maybe I can squeeze 170 out of this half tank and that would give me 340 for the entire tank. I also found out what size tires mine are, p265/65R17 .....stock is p225/75R16XL according to my door jamb sticker. My 17inch tires on them all have the same specs, 44psi max (cold temp I'm guessing) with the same weight rating. The door jamb says 41psi for the old stock 16inch tires though. I guess my front passenger is just a different type, its thread pattern is different and wider and almost looks like an offroad type of tire, but is rated for the same specs and even same size specs as the other 3, weird.

at the very lowest getting the rated 14mpg city that would give me 364 for the entire tank. Considering I don't know the exact age of the ignition components/their quality as well as not knowing how old the o2 sensors are, or if they've even ever been changed, that's not too far off if I can squeeze 340 out of it with mostly city driving this month. If it were all highway miles getting the higher 18mpg highway, is that considered driving from town to town on open highway with very little to no redlights? My town has a highway that runs all around it in a loop, but there are still red lights every so often, so I'm not sure if that's still considered city driving or highway......I've tried my best to avoid inner city neighborhood stop and go traffic though.

If it were all highway miles that calculates out to 468 to the tank(18mpg highway according to the fuel economy gov website), although nobody is ever going to have all purely highway miles in a realistic case lol.

I never heard of "16XL" tires before that apparently came stock on my truck years ago when it was brand new....I guess they're very similar to the 17's in size, having the 17's doesn't seem to have affected my mpg hugely.

maybe getting the spectre air filter wouldn't be a bad idea when I have some extra money. I guess it's just kinda hard justifying buying parts when the truck just works as is haha....I was just concerned my miles were way lower than they should be.

 

That's if you run your tank stone empty. Not really recommended. When the low fuel light comes on, there is still, supposedly.. six gallons left in the tank. I have not put that one to the test.... and I don't want to.

The gauge is NOT a good indicator of how much fuel you have burned thru. It will give you a general idea, but, math is the only accurate way to deal with it. It appears something has changed for the better though, and THAT is the general idea.

 

I seriously doubt that! More like one or two possibly three at the most.

 

Seems fairly accurate on my truck, when the light comes on, it takes right about 20 gallons to fill. Give or take a gallon.

 

~5 gallons remaining has always been my experience with Mopars. Low gas light doesn't do you much good if it's warning you when it's almost too late.