Another MPG thread, OH NOoooo!

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  #1  
Old 05-03-06, 05:50 AM
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Another MPG thread, OH NOoooo!

Okay all you pros and heavy thinkers , riddle me this one:

My work vehicle:
1994 Chevy W-4 (aka Isuzu NPR), 9,000# gvw
5.7L/4L80E eng/trans
450,000 miles total
About 30,000 miles on the present engine
About 10,000 miles on present tranny

So, here's the mystery. This truck has always gotten between about 7 1/2 and a little over 8 mpg regardless of any factors; loaded/unloaded, ac/no ac, hot weather/cold weather. Doesn't matter; long term if I averaged last 200,000 miles of fillups it would come up about an even 8 mpg.

As of about two weeks ago the truck is now averaging 9 mpg. The increase began roughly about the time I made a long cross-state run of about a total distance of 425 miles, which is somewhat unusual, but certainly not the first time I've made a long-distance drive. A 1 mpg jump doesn't sound like much, but when you're only getting 8 mpg to start with it represents about a 13% increase; the equivelant of going from 25 to 28 mpg!

No significant work on the truck that would in any way be related to fuel economy, in fact several fill-ups into the better mileage I had to replace a u-joint, so part of the better mileage was on a failing u-joint.

I've stumped everyone I know so far. The only one with a possible suggestion said it may be related to the computer making an adjustment from the long highway run, but that was two weeks ago now and as I said, not the first long haul I ever made.

Ideas? Soon as I figure it out I'll be selling it for the big bucks!
 
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  #2  
Old 05-03-06, 10:20 AM
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Did you recently replace tires? The wrong size will make a lier out of the odometer.
 
  #3  
Old 05-03-06, 10:31 AM
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Negative. Always use the same size tires. Even same brand and none have been replaced lately.

Next contestant.
 
  #4  
Old 05-03-06, 10:46 AM
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Don't tell me, let me guess.....
You put a pint of Ethos FR in the tank!

Could you tell me, the_tow_guy, where one might find a self-motivated go-getter who wants to get in on the ground floor of a great investment opportunity and might have a garage full of Ethos FR?



(http://forum.doityourself.com/showthread.php?t=262851)
 
  #5  
Old 05-03-06, 05:54 PM
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Not.

As soon as I sort through all of everyone's thoughts on the matter I am going to pick the most ridiculous and market it as the fuel saving system for the 21st century! Hey, I already have the data to support what ever I come up with. My data shows a savings of "up to" 75% [13% is "up to" 75 %, right?]

I'm leaning towards something to do with the u-joints I replaced. I can repackage some from the local parts house and sell them for $99 a piece. The tentative name will be Sav-U-Gas joints.

You want I should pencil you in as a distributer, slick?
 
  #6  
Old 05-03-06, 06:11 PM
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could it be fuel

Could it be the new fuel they are raving about?How about maybe you set tire pressure to the high side.
 
  #7  
Old 05-03-06, 06:22 PM
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Originally Posted by the_tow_guy
You want I should pencil you in as a distributer, slick?
You can call me Mr. Sav-U-Gas Joints now
 
  #8  
Old 05-03-06, 06:24 PM
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MPG tests on a road trip have to be taken both directions due to downhill/uphill over the course of miles, and also the fact that the prevailing wind is usually from west to east. That is why mileage has to be taken both directions and averaged.

This may not apply to your case if that trip was sometime back and you have enjoyed that mileage increase ever since. But for anyone else taking mileage tests on trips, remember to take it both ways and average.
 
  #9  
Old 05-03-06, 06:25 PM
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cant be

How can it be U Joints? they just transfer torque.
 
  #10  
Old 05-03-06, 06:25 PM
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Originally Posted by michael van
How about maybe you set tire pressure to the high side.
I thought of that
For a passcar, one MPG...that might do it
But on his truck, that's 13%...probably too much for a flying brick like an that just with the tire pressure
 
  #11  
Old 05-03-06, 06:29 PM
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Originally Posted by michael van
How can it be U Joints? they just transfer torque.
....he did say he'd pick the most ridiculous thing...


However, technically an out-of-balance driveshaft could affect how much torque is effectively transfered to the rear wheels
 
  #12  
Old 05-03-06, 06:29 PM
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I stick with fuel

I stick with the reformulated fuel.and maybe he took some stuff off his truck for less weight.
 
  #13  
Old 05-03-06, 06:33 PM
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Originally Posted by michael van
I stick with the reformulated fuel.
Are you sure?
These Sav-U-Gas joints are only $35 each?
Including shipping...
 
  #14  
Old 05-03-06, 06:36 PM
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I will buy them

If they make some for my Tacoma I will buy some might be the special bearings they use in them
 
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Old 05-03-06, 06:48 PM
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His vacuum advance was stuck and unstuck itself.

He stopped using ethanol-gas after he heard that the calories of ethanol are 10-15% less than that for gas...that ethanol additive brings down your gas mileage.

The weather got warmer out...more conducive to better fuel atomization.

He mounted a wind deflector.

He put the tail gate back up (or in) after watching Mythbusters where they proved that driving with the tail gate down actually LOWERS gas mileage, rather than creating better gas mileage. (I watched that episode.)

He waxed the vehicle.
 
  #16  
Old 05-03-06, 08:31 PM
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Offhand guess, maybe your new engine is broken in now.
 
  #17  
Old 05-03-06, 08:38 PM
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Lightbulb

it could have been the universasl joints, there are alot of factors that play a roll in the fuel economy of a car, some examples are: Tire Pressure; Too High and your going to blow your tires, Too Low and your going to go slower, and waste gas. Aerodynamics; If your vehicle is shaped like a box then your losing money already because again, you'll go slower, waste more gas, and that's one wierd looking car, now if your car is shaped like a needle then your on target because you're not pushing against the wind as much thus saving gas, and strain on the trans and engine, you'll also go faster too without having to pull as mush power. Where you get your gas; watch where you get your gas from i got gas from a servco (now wilco hess) one day and filled my truck up thinking i was getting a full tank of gas, instead i got a gas tank half full of water and half full of gas. Are your spark plugs or spark plug wires fouled out; if your spark plugs or spark plug wires are fouled out then it will cause your engin to skip, which wastes a ton of gas. Check/Replace your fuel filter; your fuel filter can get cloged and cause gas to get gumed up which can not only make you lose good gas but can also tear up your entire fuel system which isnt the cheapist thing in the world to fix (i know). thats all i can think of right now, i'll post more when i think of them so you can try them all you can do is try these and save as much as you can. Good Luck
 
  #18  
Old 05-04-06, 02:40 AM
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while it could be a good thing to gain 1 mpg but perhaps it means that something is going bad on the vehicle that causes less of a load on the engine and thus increasing gas mileage such as an alternater getting weak or fan clutch not engaging the fan as much just a couple of things that come to mind.
 
  #19  
Old 05-04-06, 05:13 AM
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Okay, time to de-bunk (in order).

1. New fuel. Possible, but only if every station sstarted deleivering it at the same time within the last three weeks.
2. Tire pressure. Haven't added any air lately.
3. MPG tests. On this particular vehicle, it makes very little difference whether I'm driving around town empty or going down the interstate with a car on the hook at 75 mph - prior mpg was always 8-ish, now 9-ish.
4. Price of Sav-U-Gas joints. Sorry I forgot the shipping and "handling" - add $9.95 [non-refundable].
5. Tacoma joints. Got 'em! Credit card and shipping address and you all set, MV.
6. Vacuum advance. How old do you think this truck is Dave??? Vacuum advance went out with disco.
7. Ethanol. Don't think there's any stations in the area selling ethanol-added fuel. At any rate the mpg differential doesn't seem to matter where I gas. Within the last month I've put in Hess, BP, Shell, Racetrac, Sam's Club, Chevron, Sunoco, Circle-K, and I've probably forgotten a couple.
8. Weather. Yeah, warmed up from daytime average of 85 to 87; but the long-term "base" average is 8-ish including middle of summer and middle of winter (when the temps get down into the 60's!).
9. Wind deflector. Nope.
10. Tailgate. Ain't got one (it's a tow truck).
11. Wax. Needs a wash and a wax BAD.
12. Less weight (oops, missed seeing that). Nah. Truck weighs 9,000# and alwasy has the same "stuff" on it.
13. New engine break-in. Don't think so; I might go for that if the mpg increased a little at a time over 6 months or so; plus, 5 years ago the previous engine would have been broken it, too. This increase was literally overnight.
14. U-joints. As with other stuff, the u-joints weren't always worn out. Two years ago they were brand new and mpg still 8-ish.
15. Gas supply. Noted above. I fill up at any of a dozen stations and get hit the pumps once a day.
16. Fuel filter, et al. We maintain the trucks meticulously. Oil & filter 3k, tranny fluid 10k, tranny fluid and filter 20k, fuel filter 5k.
17. Accessories. Recently replaced the fan clutch, but I would have expected the same or even lower mpg with that (and it was done couple of weeks before the upswing in mpg).

Gas reformulation would seem to be about the only possible one. Anybody think it would give me a 13% boost? Seems like an awful lot and would you expect prettty much all stations to deliver it at the same time?

 
  #20  
Old 05-04-06, 07:17 AM
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OK TG
This will be long, but please bear with me

When the new reformulated fuel came out, it was first only seasonal and regional…sometimes even to the different counties in the states
They did say that certain vehicles could actually suffer a reduction in MPG

I personally had a vehicle with a large F.I. domestic engine that suffered from this reduction

Although the powers that be did admit there could be “…instances… as high as -10%“, mine was much worse
At first it was just “winter gas” for my area
My state got the reformulated fuel only in the winter
I would write off the drop in mileage to the cold weather…at first
It was high…but hey….big engine, short trips….cold weather…
You’d almost expect a 10% drop
…but it was higher…
And it wasn’t that bad in the winter before….

I got suspicious when I’d get a few “good mileage” tankfulls in the winter
I realized those tanks were filled up in another state (that I visited often) that did not have reformulated fuel
I’d always fill up before heading home as the price was better

Over the next few years, as my local pumps had a longer and longer “oxygenated” season, and eventually to all-year long reformulated gas, and my “MTBE-Free” pump stayed that way for quite a while, I got some pretty good data

All of my vehicles got lower gas mileage with the reformulated fuel
None as bad as the FI 5 liter

It was horrible

Absolute best case scenario, -12% with the reformulated gas
Winter it was often as bad as -30%

Now, picture this
What if I had purchased the vehicle years later…and only had run my local reformulated fuel
I’d think that the -12% to -30% would be “normal”, right?

What if my local area stopped requiring the oxygenated fuel?

I’d get an instant 12%+ increase in MPG
Not knowing that’s more like what it’s “supposed” to be


Now, for the regs….
The national requirement for all states to have oxygenated fuel is being lifted
It has already been done so in some regions

As the additives are costly, and I’m sure the petroleum companies wouldn’t mind NOT adding it (but keeping the prices the same), I’m sure they’ll jump on it pretty quickly, if they haven’t done so in your area already

The question is, is it possible that you are now running on re-reformulated (non-oxygenated) gas?

(The EPA site is not accurate or up-to-date on who has it and who doesn't, you can't go by them)

Do I believe a “new”, non-oxygenated gas mixture could up your mileage by 13%?
Absolutely, there’s no doubt in my mind
And it would do so instantly with no other indications that something is different
 
  #21  
Old 05-04-06, 08:21 AM
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Mexican Overdrive

Perhaps the long trip cooked some carbon off the throttle-body
at some place where it was becoming coked up??:
D'ja head out towing a '58 Caddie ElDorado and come back with a Yugo????
 
  #22  
Old 05-04-06, 10:36 AM
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Slick: I'm not real well-read on the various formulations, but as far as I know the oxygenated fuel has never been used around here, so we wouldn't have summer/winter gas differences. Ditto ethanol. Every once in a while I'll run a cross a station with an ethanol sticker on the pump, but to the best of my knowledge none of my regular pit stops uses it. We have no air pollution problems in this neck of the woods. It seems unlikely that a dozen different staions and brands would suddenly make a switch to a fuel formulation that would up my mpg overnight. Since I fuel daily and rarely twice in a row at the same station or even brand, I have a pretty good cross section I think. I now have something on the order of 15 fillups in last 2-3 weeks, which would take most people several months to do.

Qwincy: Would make about as much sense as anything else.. Outbound was a '94 Camaro destined for the US Virgin Islands via one of the east coast Fla ports [purchase sight unseen on EBay, would you believe?]. Return trip was with a Mazda. Doesn't seeem to make much difference; I'm getting the better mileage even with a fairly heavy load on.

The search goes on.....
 
  #23  
Old 05-04-06, 11:15 AM
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Originally Posted by the_tow_guy
Slick: I'm not real well-read on the various formulations, but as far as I know the oxygenated fuel has never been used around here, so we wouldn't have summer/winter gas differences.
Yeah you wouldn't have the summer/winter thing anyway

But it's been manditory (federally) year-round for seven years
They don't even have to put a sticker on the pump anymore
Some less populous states had "waivers" and didn't need it
I don't know about FLA
It's populous enough I figure it has (had) to have it

What I'm saying is the "new" reformulated gas is minus the mileage robbing additive
It was contaminating water supplies

If your county/state stopped requiring it, all the gas stations would get it about the same time

The feds stopped rrequiring it this month
 
  #24  
Old 05-04-06, 03:30 PM
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If that's the answer, I'm happy; means it'll stay up (until the next brilliant beurocratic idea). Cool.
 
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Old 05-04-06, 05:04 PM
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Originally Posted by slickshift

Absolute best case scenario, -12% with the reformulated gas
Winter it was often as bad as -30%
This is slightly off-topic, but being you raised such a drastic change in mileage...I had a 79 Chev.1/2 ton that would get about 9.5 in the winter and get up to 12.5 in the summer. Quite the difference. Temperature swings could be 110 degrees or more outside!
 
  #26  
Old 05-05-06, 08:52 PM
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You said truck used to get a little over 8 mpg sometimes and now is getting 9 mpg, so the diff would be less than 1 mpg at sometimes, also when you say " regardless of loaded etc " it doesn't make sense unless you're counting " average " mpg.
And remember percentages are relative it maybe 13 % but given low mpg to start with it makes not too much of a diff ( being a tow truck of course ), anyways Im not trying to put anybody down just trying to be objective , interesting post ...
 

Last edited by LouBazooka; 05-05-06 at 09:08 PM.
  #27  
Old 05-06-06, 10:51 AM
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Well, I can tell you the difference is noticeable. If you were saving 2-3 gallons of gas a day, believe me you would notice it and be curious where the savings was coming from. The range ran 7.5-8.25 previously and now is always above 9 (not counting the time the pump cut-off at one of the stations with a max $ programmed in). The fact that it jumped from 8-9 is significant exactly because we are talking about a very low mpg. If the vehicle originally got 35 mpg and now got 36 (an increase of less than 3%) it would certainly be neither significant nor noticeable. You could probably achieve that by changing your tire pressures from 25 psi to 35 psi. If you started out getting 35 and got a 13% increase - to nearly 40mpg - that would be tough to write off to "averages" or any other casual factors.

When I say loaded or unloaded, I mean the truck gets prettty much the same regardless of how it's driven; just the nature of the beast. I can drive100 miles with an F150 on the hook and get about 9 mpg (now), turn around and make a return trip unloaded and get perhaps 9.2 mpg (or sometimes 8.9 if I'm now going into a headwind).
 
  #28  
Old 05-06-06, 11:00 AM
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P.S. Have you ordered your Sav-U-Gas joints yet, Lou?
 
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Old 05-06-06, 05:38 PM
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I have heard that engines run real well, and loose...just before they are ready to blow!
 
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Old 05-06-06, 05:40 PM
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Still got two years warranty left on it, so as long as it blows in the next 24 months, no problem.
 
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