As others have stated, if you have a V6 getting 5 mpg, then you have bigger problems than low air pressure or a dirty air filter. A Ford 3/4 ton V10 pulling a gigantic fifth-wheel trailer at 70 mph uphill gets more than that

Any updates on this situation? I have found in the past that mysterious changes for the worse in gas mileage are often tied to failing emissions components. So, O2 sensors and EGR valves would be the place I would start.

I don't know about the law in NY, but here in Michigan, there is a law that requires, if you request, a repair shop to either give you back your old parts or at least show you them if returning them to you is not practical . I would look into that and use it to your advantage if possible, especially if you are going to continue to pay top dollar for the dealership to work on the truck.

 

Believe me, this has been boggling me because the truck now seems to be back to normal. (or as normal as it has been). I think I'll change the O2 sensors and plugs anyway because even before this, I'd noticed a small drop in MPGs. From 14city to 11ish. The dealer told me that this is due to the ethanol and addatives in the fuel. "Your truck wasn't built to run on corn", was the exact wording. I took this as B.S.
The only reason that the dealer was doing the work was because it was under warranty. Now that that's up, I'll be doing whatever I can, myself.

Overall, I'm disappointed with the MPGs on the V6. I definitely should have sprung for the extra $$$ and gotten the V8. I thought I'd be saving money on gas with a V6, but with a truck weighing close to 4500 lbs, the V8 actually does better.

I'm sure I'll be on here a lot more looking for advice now that I'm doing repairs myself. Thanks for the help.

 

I have heard the old "ethanol is ruining your car" before...

Sure, you can't run E-85 in it and expect no problems if it is not a flex-fuel vehicle. That being said, as long as I have been driving, Michigan has required ALL unleaded gas to be mixed with 10% ethanol. You cannot buy pump gas here without ethanol in it (I don't know if 108 octane race fuel has ethanol in it or not, but that crap is $$$$).

So, if that is the dealer's position, ask him why Dodge continues to market vehicles in Michigan knowing they will fail. He won't be willing to say that his company (well, the company that he depends on for a job) is selling products that it knows cannot function in my state.

Sarcasm on /// If possible, get his position in writing and mail it to me, and I will file a class action suit against Dodge for offering a defective product to the market in my state /// Sarcasm off

 

I knew it was BS when he said it. I told him that "That's not my fault. If the truck was built wrong they need to give me an engine that was 'Built to run on corn'." He didn't have much of an answer for that.

 

It's not.

 

I wouldn't just go and change 02 sensors for the heck of it. They are expensive. And if you don't have CEL, chances are nothing is wrong with them. If something was, your computer would tell you. So just changing them because you saw a slight low in fuel mileage is not a good idea.

And Madison is right, these engines weren't built to run on corn and they run better on 100% gas. What he said isn't B.S.

It really sucks for smaller engines (motocross bikes, lawnmowers, that sort of thing) because it's even harder on them. And now-a-days it's about impossible to find 100% gas.

 

Well, I believe that is is, in fact, BS. Maybe I have been duped by the Michigan corn growers propaganda, maybe not.

"Research has demonstrated that all vehicles can run on E10 (10% ethanol, 90% gasoline) with no adverse consequences such as corrosion of certain metal parts."

http://michigan.gov/dleg/0,1607,7-15...3812--,00.html

Furthermore,

"every automobile manufacturer warrantees their vehicles to use up to E10 and many automakers recommend its use because of its high performance and cleaner-burning characteristics"

http://www.micorn.org/ethanol/index.html

In Michigan, they don't even have to label the gas as being blended with ethanol anymore. Every pump I have ever seen has a little label that says it contains up to 10% ethanol. I have been driving for 16 plus years now, and I have NEVER seen anything else.

Obviously, you put E85 in a non-E85 vehicle, and you will have problems. But straight from the pump E10 has been being used for DECADES.

 

You can run an engine propane, natural gas, dead babies, HHO, etc. But was it meant for that? No. It was meant to run on 100% good ole dead dinosaur. Its HP numbers are off of that sweet sweet T-rex, nothing more.

E10 LOWERS power, and fuel economy, sometimes more than what seems mathematically possible.

 

I suppose I am one of the lucky that 100% gasoline is still available in my area. I have noticed that it makes a HUGE difference in performance when I use anything other than 100% in my 4-wheeler But that is a verry precision machine designed strictly for performance. My truck however seems to do about the same on whatever I put in there but then again it has 260K miles too so it is well worn in. I recently took an 8 hr drive and running at between 75 and 80 mph 90% of the time with a 5.2, 5sp, 3.92 rear end, and relatively heavy tires and wheels (30" tires on 17x9 alum wheels). I averaged right at 17 mpg. Not bad for a tired ol Dak.

 

The lower MPG may also be due to winter mix gas. I live in Florida so I don't have to deal with winter gas but I hear guys from up north on other forums all the time complaining about lower MPG and less power on winter gas. I don't know what they do to the gas for winter. It could also be because at colder outside temperatures the PCM changes the air fuel mix, probably runs richer than usual. I don't have to deal with that much either, but have read about it on other boards.

Still, it can't hurt to replace the plugs. On a 2004 even if it only has 40,000 miles on it it is time for new plugs. If the 3.7 has a cap and rotor and plug wires it's time for those too. Whether to replace the O2 is really a personal preference. Depends on the mileage on the truck. I understand they can get lazy around 80,000 miles and affect the MPG without throwing a code. I replaced both of my own upstream O2's as a maintenance item at 95,000 miles, and I replaced the MAP sensor then too even though I had no codes for either one.

The Lucas treatment may help offset some of the effects of ethanol. I don't know much about Lucas but I know Marvel Mystery Oil definitely helps offset the corn juice gas. MMO restores the lubricity of the fuel and its upper cylinder lube properties improve power, at least for my truck it does. I like MMO because it works but is not near as harsh as Lucas, Redline or some of the other gas treatments out there. I use MMO in every tank of gas I buy and my truck runs a lot better with it. I get a little better MPG with MMO too.

Jimmy