I'm Losing It

Gas Mileage, that is, on my 2000 Rodeo LS. I figured an 80 Liter (21.1 gallons) tank should go about 350 miles at an average 17mpg. Well I can't even break 250 - that's about 12mpg!?!?! With gas prices skyrocketing, it's getting ridiculous to actually SEE my needle drop. I just had a whole fuel system clean a few months ago, use nothing but 91-93 Octane; Plus or Premium gas, and every 3,000 I drop in a bottle of Chevron Techron, I have new plugs and all that jazz....

...but the mpg seems to just be getting worse and worse as the prices get higher and higher.

I just got this Rodeo last summer, and remember being able to hit 100 miles at about the quarter tank mark...now I'm hitting less than 120 miles at the HALF tank mark, this should be illegal. My 15 year old 1990 Trooper was getting the same MPG as this, I thought maybe buying a newer truck would help that out...

What the heck should I do?

Guess I'll take it in for YET ANOTHER tune-up - 3 tune-ups so far - less than a year I've owned it. I don't know what else to do.

Try using 89 octane and see what happens.

Also, if the weather has been wet or cold, you may want to add a bottle of HEET to soak up any water in the tank.

You think I'm runnin' too rich?

89 is normal mid-grade, right? Like Plus...I'll give it a try, as I usually go 91+ Premium or Ultra (93).

Your truck was designed to run 87 octane. if you notice pinging under acceleration (up hill, it will be more noticable) then bump up to the next grade. High octane gas will not give you better gas mileage.

How are you calculating your MPG?

If you are just going by the miles on the odemiter verus the amount of gas on the gauge your fuel sending unit may be faulty.

See the FAQ for reasons for lower gas mileage fixes (the biggy is a leaky Intake Manafold gasket (lower the mileage by 3-4 MPG), which is a common problem on +98 Isuzu's)

Thanks for reply.

I'm calculating mpg by using the trip meter and how much gas goes into next fill-up.

Used to average around 17,18. Seems everytime my gas light goes on, the fill-up is less and less, used to leave about 4 gallons behind, but last fill-up, gas light came on and I only put like 12 gallons in? Faulty gauge, eh?

Didn't know the Rodeo was designed for low-grade gas. I will start putting in nothing but regular.

Getting an alignment today, as I've noticed a vibrating steering wheel lately, at higher speeds. Hopefully that will help some.

You should be running 87 octane in your truck. Like Ryan pointed out, this is what these trucks are spec'd for. You are dumping money down the drain buying 89, 91 or above gasoline!! I highly doubt you need another 'tune-up'. Sounds like you are all up to date there. 15-20MPG's is normal for the 1998+ 3.2L. About 250-300 miles per tank is normal. If you consistantly get less than 15mpg's, you could have low air pressure in the tires. Another thing to watch for, is don't use the windshield defrost setting (or A/C) unless you need it. Running the defrost cycles the a/c compressor which will reduce your MPG's.
G/luck
Joel

Ok.

87 octane.
getting an alignment today.
checking tire pressure.

someone also said run some HEET in the gas to soak up any water, etc, it's been raining alot lately and the weather just now is warming up from winter 30's-40's to the 60's.....so mine as well give that a try too.

All these things will be done by this evening, as well as another Chevron Techron add.

Driving to NJ from DC tomorrow so I will def. have results to publish :)

....Getting an alignment today, as I've noticed a vibrating steering wheel lately, at higher speeds. Hopefully that will help some.

I would not waste money on a front end alignment unless your front tires wear unusually. Vibrating front end typically is a tire issue. Either tire balancing, bad/shifted cord, or just a worn tire.
G/luck
Joel

Wow, I really suck at cars.

I guess I will have them check the tires first. I just figured it was an alignment issue. The tread is pretty low, maybe new tires are in order.

The vibration gets really heavy though, specially when applying brakes on the highway, it's almost out of control steering wheel vibration.

assuming that your gas gauge isn't off (most likely it isn't), try filling her up (use 87/89 octane gasoline and don't top off) and trip the meter. then, when the tank is 3/4 full, fill her up again (don't top off). Divide the miles driven on that quarter tank by the amount of gasoline put back in to fill it up. this will tell you your true gas milage as close as it can get.

if the steering wheel is shaking try checking out the egr valve. carbon buildup in an engine can cause this problem.

also, only add techron every 3k miles. adding it too often can cause problems.

vibration at the steering wheel is usually caused by wheels that need to be balanced (I had the samething happen to my 2000).

If you are the orginal owner the fuel sending unit fix is covered under warranty.

If you are going to take it in to the dealer, have them leak check the IMG too.

Also, having a clean EGR (and Port ) and PVC is important too.

Well, I took the truck to my tire place. Guy advised all 4 tires needed to be replaced. Now that I recall, some people told me a few months ago that my tires were getting pretty worn....so I'm sure that wasn't helping any. Could extremely worn tires really affect my mpg as much as this?

As far as Techron, I haven't used it all that much, usually once every time I get my oil changed. What are the side-effects of using it within the 3k interval?

I feel compelled to point out that on newer cars all a tune-up is is changing the spark plugs. There are no adjustments or fine tuning to be done like on older cars. And, if you put in platinum plugs, those last alot longer than standard, so frequent tune-ups would be pointless and a waste of money. :2cents:

Interesting thread. Antoher thing to consider on gas mileage is the seasonal changes in the gasoline blend. It has been my experience that I always get lower mileage with the winter blend. It's been less pronounced on some cars than others but on my Rodeo, the winter grade has cost me 15-20%. I get about 17-18 in mixed driving in the summer (with the air on) but only about 14-15 in the winter.

I am an engineer and I track my gas mileage with statistics just like it was a chemical process. And this trend holds for the last seven years. I always get poorer mileage in the winter.

Road conditions and colder intake air play a part in this too but I think it's mostly the gas. The reasons gas prices always go up in the summer is that a) demand increases, b) summer blend is more expensive to produce, and c) the oil companies never miss a chance to jack up the price.

And that comment someone made about the A/C in defrost is true but not as much as it used to be. Vehicles these days cycle the compressor on and off and drop it out completely on hard acceleration so they aren't the gas drain they used to be. In fact, you probably will get better gas mileage in the summer with the A/C on at highway speeds than you would with the windows down. There's a lot of drag created with the windows down.

So quit hemorrhaging cash trying to get your mileage up until you see what the summer brings.

Just my $.02.

JWS
'99 LSE 4WD

As far as the alignment goes...

I had greater wear of the right front than the driver's side, so I took it in for a new pair of front tires and an alignment. Front right was off .22 degrees, not surprisingly. Drives much better now.

there may be a problem with your fuel sending unit

Just got back from trip. Mostly highway, did 290 miles on 13 gallons, that's almost 22 mpg. I'm a happy camper, as the truck is supposedly rated 17/21.

I figure it's the new tires, I had no idea my old tires were so bad that they would affect my mpg that much.

Also, running 2 tanks so far of regular 87 octane...everything is kosher.

Thanks everyone for replying.

Hard to believe tire condition could play that big a factor. Tire inflation, on the other hand, could be significant. What tire pressure are you running on the new set? The recommended pressure for the 98 and 99 is 26 psig.

I would bet yours are higher than this. When I bought new tires in December, the tire iron jockeys put no less than 35 in any of them and even put 48 in one of the front ones. Fortunately, I checked them before I hit the open road. They also left several of the lugnuts loose on the FR. This, I didn't check before I made a 900 mile road trip. I lost two lug nuts and there were two more that I spun off by hand. It's a wonder the FR tire didn't just come off.

Higher tire pressure will usually get you higher mpg (especially at highway speeds) just because there is less tire in contact with the road and therefore less friction. (If your old tires were really bald, they would have had higher friction because they would have been touching the road all over instead of just on the treads.) If you find your new tires are set at 30+ and you drop them back to 26 you may loose an mpg or so. Of course, you will also be less likely to turn your SUV over.

So check that tire pressure!

Another $.02. Not sure what part of the country you are in either but you could be starting to get some of that summer gas there which would help

JWS
'99 Rodeo LSE 4WD

When my last set of tires went bad, I had a horrible vibration! Even balancing the tires wouldn't help, as there wasn't much tire left.