I'm a little disenchanted with the the gas mileage on my Expedition after receiving and installing my Diablo Predator.

I Took my first highway-only trip since uploading the Predator tune this past weekend. I had 91 octane gas in the tank and one passenger with one bag each and the back seat removed. It was all highway driving holding around 72mph and got 16.2mpg on one tank. Not bad but I've gotten 18-19mpg under similar conditions without the tune.

Now here's the kicker. Just before I received the Predator I took another highway trip. Same speed and driving conditions using 87 octane gas and that time I was LOADED DOWN. I had five passengers plus me and all of our stuff including a hard shell roof luggage carrier (noticeable wind drag) and a loaded bumper cargo carrier. That tank gave me 16.5mpg! I thought that was great considering the load so I was expecting an improvement with the Predator tune installed on my most recent trip.

All the figures were checked with a calculator and my odometer and confirmed with the trip meter on my GPS–not using the on-board trip computer (although it was very accurate too.)

If you think about it, I actually got worse mileage WITH the Predator than without (and I was being very consistant with my driving style)

I'd like to hear from anyone who has gas mileage stats to go with their Predator. I know it's not all about the mileage (I wouldn't drive an Expedition if I was concerned!) But you'd think at least the 91 octane in the tank after the Predator tune would have helped me out.

 

A few questions:

1. Was the 91 octane fuel a blended fuel (ie, alcohol in it)? Alcohol in fuel can lower mileage.
2. Was each trip identical, such as weather conditions (humidity and air temp impacts mileage)? Trip course the same? (I get worse mileage driving up to Tennesee in the mountaints than coming back down to Georgia.)

 

I have seen no change in milage either but more accel and passing ability. Funny I to check Milage/ odometer with a GPS too . Try a tank of Texaco gas seems to be better for milage. getting 18+ now was at 17ish before

 

Unless something's changed *very* recently, Texaco gas isn't going to do anything for you. All the major oil companies indiscriminately swap gas from their refineries to other OilCo's resellers, just to save on distribution costs. Gas is gas. There are only two exceptions to this:

1. Chevron and Union 76 have their truck drivers put additives in, so the gas from these trucks is a little different.
2. If you happened to buy from a station whose stock of gas had sat for a *very* long time, like 30 months or so, there's a chance it could have more water in it. I've only heard of this once in 30 years of being around cars.

 

Explain why Amoco premium is clear (remember when it was blue?) and others slightly brown... or that Shell gas always pings with the tune in my truck. There is a difference here.

Very easy to get water in gas.... just fill up right after the gas truck has pumped gas into the ground. If you've every stuck a water stick in a ground tank you know that many gas stations have water in their tanks.

 

I'm not aware that any alcohol was blended in. The trip with the heavy load, lower octane, and better mileage before the tune was from Dallas to Atlanta (mostly flat). The 16.5 mpg mentioned earlier in this string was an average over about 2 1/2 tanks. The second trip with 16.2 mpg after the tune and with higher octane was from Dallas to Houston (mostly flat) averaged over 1 1/2 tanks. Tire pressure was consistent on both trips as well. To my knowledge, the fuel types are the same throughout the South and Southwest. The temperature was about the same on both trips–between 85 and 95 degrees. Not sure about the humidity, but here in the south it's always humid in the summer and fairly consistent across the entire region.

As a rule, I always try to buy the better brands of fuel like Shell, Exxon, or Mobil and these trips were no exception. Of course I'm not complaining about the difference between 0.3 mpg–both are quite acceptable given the vehicle. It's the drastic difference between loads and octanes on those trips that just don't seem to add up. And now the tune requires higher octane fuel at a higher cost and it just doesn't feel like I have anything to show for it but a bigger dent in my wallet. (I discuss my lack of enthusiasim for the performance gains in another thread)

I guess I should calm down a little bit. The biggest reason I bought the Predator was to accomodate a speedometer calibration for the bigger tires I'm about to buy. Once I put 315/70/17's on a 4X4 Expy all hopes of reasonable mileage are out the window anyway! And anything's better than the mileage on my Bronco with a C6 3 speed and 33" mud tires! Thanks for the responses.

 

Can't talk about Amoco...we don't get that around here. Maybe they're the exception and keep their gas supply within house. Come to think of it, that would be consistent with there being spots in the country where you can't get it. About the Shell gas...maybe knowing you have Shell in your tank makes your ears better...

But I can tell you that the OilCo's definitely do swap gas. Until it hits the trucks of those who put additives into it, it's essentially a commodity product.

True enough...the good news is that a little water in your gas isn't likely to be a problem. Those who are really fussy about minimizing water in their fuel do things like find out what days the trucks come to their stations, and fill up the day before...early in the AM when things have cooled and the water has settled to the top of the tank (pumps take from the bottom)...more work than I'm willing to go through and I've never had a problem with too much water in my fuel. (Knock on wood.)

 

Water heavier than gas, it will be on the bottom. Water s.g. 1.0, gas lighter of course.I would think that's the problem getting gas when the tanker is there, they can stir it up.

 

Major "duh" on my part...of course you're right, water is considerably heavier than gasoline. I guess gas pumps do somehow take from the top of the tank, or at least not the very bottom. Filling up earlier in the AM suppposedly also has something to do with allowing the water and gas to cool a bit, but I'm not sure what the significance of that would be.

 

Years ago in my younger days I worked graveyard shift in the summer at a gas station. We had to measure water levels in the tank every night. We would put a powder on a huge wooden stick with inch markings on it and put the stick down the tank. The compound would change color from the bottom up telling us how many inches of water was in the tank. If it got above a certain level they would pump it out. I always measured before the tankers came in, if I did it afterwards the whole stick would have discolored spots!

People would pump that water/gas mix into their cars!

 

If I may interject, this discussion about gas and water, though informative, is straying from my original post about the Predator and gas mileage statistics. Maybe it's not my place to mention this but I was already advised to start this post when I had brought it up in another thread.

 

Renkenj have you tried the new revision r52 with stock settings
I am still noticeing better milage with texaco even when 1/2 mobil I use a lot of gas
I am glad some one started this post

 

would you belive 52a is out already seems like yesterday 52 just came out oh it did

 

renkenj no one else here gave any milage stats just the old water in the gas jabber

 

Its not straying from your question, its an explaination of the possible reasons for gas mileage differences.