MPG Testing AR-5 + 93 Octane

Much is made about the awesomeness of driving a 5-speed VX, but one thing we haven't seen a lot of is MPG gain analysis. After driving to WI and back in the wife's new fuel-efficient turbo Forester I decided to do a test run of my own with the VX, but this time using premium fuel (93 octane) and some MPG saving tricks I've learned through the assistance of my car PC, most notably coasting down long hills with the clutch in rather than with the transmission in gear. Below are my findings:

Here's a map of my route through the mountains in VA, WV, and OH then across a mostly flat area to Dayton. (Btw it includes 3 toll booth stops where you have to restart your uphill climb from zero. :mad:)

http://www.vehicross.info/gallery/da...G_Test_Map.png

Here's the data from my car PC real-time dashboard:

http://www.vehicross.info/gallery/da...0624-00057.jpg

And here's the analog data. :) (Isn't it weird that the trip distance is slightly off? Yes I made absolutely sure to reset them at the exact same time.)

http://www.vehicross.info/gallery/da...0624-00055.jpg


Price and quantity at the pump:

http://www.vehicross.info/gallery/da...0624-00053.jpg

Obviously there's a big delta between the fuel consumed value on the PC and what I saw at the pump, but it's pretty typical in my experience (OBDII tool uses MAF readings to generate a best guess which coincidentally always seems to be optimistic). But if you take the more realistic/pessimistic fuel consumption value from the pump and take into account that I'm running 3% taller tires, I calculate 19.71 MPG for the trip. Keep in mind that's with the AC running the whole time, plus my VX has larger tires, heavier rims, a full-size spare on board, and 150 lbs. of Kilby skid plate underneath. I'll track my fuel economy on the way back (which involves a greater net elevation change but still lots of uphill and downhill grades) and let you guys know how it goes.

So how does that compare to a VX with the auto trans? I had all these same mods on my last VX and I think 15-16 MPG would be pretty realistic for the same trip (although honestly I've never ran 93 before). If so that's an increase of anywhere from 23% to 31% better than the auto. :thumbup:

I ran almost the same route, from Dayton, OH to Charleston, SC, through the WV turnpike, bone stock with bad wheel bearings, I got over 20mpg by the pump and GPS mileage. SO your 19ish is probably realistic. I don't 93 octane matters, the computer isn't programmed for it. I think if you did the same experiment in the winter, you might see a decent difference (no AC and higher O2 concentration)

Excellent idea. I'll check mine in a few weeks after a little project I'm working on is complete ;)

But what I have noticed, is that before, I was getting around 230ish mile per tank *if* I was lucky. I'm consistently getting over 300 mile per tank now (87 octane only). Sooooooooooooooo much more pleased now.

I forgot to mention that the fuel light hadn't even come on yet, so given the numbers 400 miles on a tank might very well be possible.

Chris what time of year was your trip?

eternal what gear oil do you plan to run? Buffy put in Royal Purple 10w30 but I replaced it with 5w40 for better summer performance. I only did it as preventative maintenance since everything was fine, but I feel like the shifting is smoother than before. Fuel economy is best ever now also, though I'm not sure if the weight shift had anything to do with it.

Ash,

FWIW, I measured 21.5 mpg on the last tank in the Amigo (90% Hwy but heavy traffic). It has the 3.2L & 5spd so that is comparable to what you're running but I think the Amigo is significantly lighter than the VX so ...

Tom

P.S. I don't keep track of it in the VX since it's soooo depressing:). I think I get better mpg in the 7 Ton Coachman with a 6.8L & auto tranny.

It was 27DEC:)

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Originally Posted by vt_maverick

eternal what gear oil do you plan to run? Buffy put in Royal Purple 10w30 but I replaced it with 5w40 for better summer performance. I only did it as preventative maintenance since everything was fine, but I feel like the shifting is smoother than before. Fuel economy is best ever now also, though I'm not sure if the weight shift had anything to do with it.

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RP 10W-30 FTW. This weekend it looks like I'll be putting ~750 miles on it, so hopefully I can get a better assessment of the gas mileage.

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Originally Posted by vt_maverick

... coasting down long hills with the clutch in rather than with the transmission in gear.

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No ... no ... no!!!

Yes, to slipping it out of gear & coast down hills but never, ever, ever, never, ever ride the clutch. Every penny of fuel you save will be lost in an early clutch replacement/rebuild. Coasting down hills with the clutch depressed will cause the early demise of the throw-out bearing. Driving with your foot resting on the clutch (but not depressed) will also cause additional wear on the throw-out bearing but will also cause wear (& early demise) of the pressure plate.

Sorry to be so emphatic but it's a sensitive issue with me after teaching 6 kids to drive.

Similar issue with resting your foot on the brake whilst driving. Even light pressure will engage the brakes a little causing extra wear & killing mpg.

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Originally Posted by tom4bren

No ... no ... no!!!

Yes, to slipping it out of gear & coast down hills but never, ever, ever, never, ever ride the clutch. Every penny of fuel you save will be lost in an early clutch replacement/rebuild. Coasting down hills with the clutch depressed will cause the early demise of the throw-out bearing. Driving with your foot resting on the clutch (but not depressed) will also cause additional wear on the throw-out bearing but will also cause wear (& early demise) of the pressure plate.

Sorry to be so emphatic but it's a sensitive issue with me after teaching 6 kids to drive.

Similar issue with resting your foot on the brake whilst driving. Even light pressure will engage the brakes a little causing extra wear & killing mpg.

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+1, had to go back and re-read that to find out when that was said *lol*. Yeah, every time you put in the clutch pedal = wear. The only time I have the clutch depressed while in gear is when I'm holding it steady on an incline @ a red light, so that I don't roll back when the light turns green. My car has hill assist, which is awesome, but old habits die hard, and I hardly ever use it :)

Who drives with their foot on the brake? *lol*

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Originally Posted by eternal21

The only time I have the clutch depressed while in gear is when I'm holding it steady on an incline @ a red light, so that I don't roll back when the light turns green.

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Sorry but that's a no no as well ... mebbe even more worser. If you must, use the e-brake to hold you in place till the clutch starts to take hold.

Personally, I've just gotten use to being quick on the pedal & don't use the e-brake except in extreme circumstances.

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Originally Posted by tom4bren

Sorry but that's a no no as well ... mebbe even more worser. If you must, use the e-brake to hold you in place till the clutch starts to take hold.

Personally, I've just gotten use to being quick on the pedal & don't use the e-brake except in extreme circumstances.

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Oh, I know it's bad, but it'll be something I do until the day I die. Something about always finding that perfect balance intrigues me ;)

Thanks Dad, I refrained from holding the clutch in on the way home and I think I heard a small gasp of relief from the bearing. ;) Seriously though, don't you just offset whatever savings you gain on the pilot bearing with wear on the clutch and synchros from having to shift and re-engage again? It certainly doesn't feel as smooth to shift in and out of gear as it does to hold the pedal down and let it go.

P.S. MPGs were even better on the way home. I'll post numbers later.

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Originally Posted by vt_maverick

Thanks Dad, I refrained from holding the clutch in on the way home and I think I heard a small gasp of relief from the bearing. ;) Seriously though, don't you just offset whatever savings you gain on the pilot bearing with wear on the clutch and synchros from having to shift and re-engage again? It certainly doesn't feel as smooth to shift in and out of gear as it does to hold the pedal down and let it go.

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Yer welcome Son:)

It depends on too many factors to give you a straight answer. On some cars you can slip it out of gear without pushing in the clutch (can't on my Amigo though so I assume can't on your VX either). Considering how much I have to 'row' through traffic, I don't see how an extra shift now & then to take advantage of coasting will make an appreciable difference on clutch longevity. On a bad traffic day, I'd conservatively estimate that I push in the clutch 1000 times on my commute home. It also depends on your driving habits like how much you feather the clutch when shifting & stuff. Ideally each shift is done at a constant speed & acceleration/deceleration is done after the shift - that gives you the smoothest shift and will make your clutch last the longest.

I get about 20mpg highway my self on my 2000 trooper 5 speed. I dont think you'd need the 91 octane since I get my mpg using regular gas with whatever ethanol content they have now days. I've been wanting to give my mpg a test with ethanol free gas a place near GWNF has.

I'm most excited about the full size spare on board, as I'll be mounting mine on the rear in the near future, and I was worried about how it might affect gas mileage.

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Originally Posted by eternal21

I'm most excited about the full size spare on board, as I'll be mounting mine on the rear in the near future, and I was worried about how it might affect gas mileage.

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Probably not at all. I didn't notice any difference whenever I stopped carrying mine. The roof however is an entirely different matter.

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Originally Posted by tom4bren

Probably not at all. I didn't notice any difference whenever I stopped carrying mine. The roof however is an entirely different matter.

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I can imagine. Roof mount = wind resistance FTL.

I get around 17 MPG in town with mine (5-spd and 35's) but just got 19 MPG while driving out to the coast last weekend. I also got around 18-20 on the drive out to Moab, with cruising speeds around 75 the whole way. Mileage depended on if I was driving across the flat bits of Idaho or through the hills in Oregon.

Results from the way home...

http://www.vehicross.info/gallery/da...0626-00060.jpg

http://www.vehicross.info/gallery/da...0626-00061.jpg

(Gas is like $0.40 cheaper per gallon in VA. :eek:)

http://www.vehicross.info/gallery/da...0626-00062.jpg

Calculated MPG was 20.45 after adjusting for tire size. :) Keep in mind that we live in the mountains of Virginia, so that's without the benefit of the additional downhill time you'd have driving further east.

Also for anyone interested in oil consumption I burned a full quart on the way to Dayton but barely half a quart on the way back.

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Originally Posted by Etfren

I get around 17 MPG in town with mine (5-spd and 35's) but just got 19 MPG while driving out to the coast last weekend. I also got around 18-20 on the drive out to Moab, with cruising speeds around 75 the whole way. Mileage depended on if I was driving across the flat bits of Idaho or through the hills in Oregon.

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Now that is damn impressive. :thumbup:

I will say that the ethanol content makes a huge difference pending the vehicle and loading. WHen I towed the VX out to Moab behind my expedition, I went from 9-10mpg with ethanol to 12-14 once I hit WY I think, maybe KS. That included all the mountains and everything. Our trucks were never designed with ethanol in mind, so it may make a difference.

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Originally Posted by Marlin

Our trucks were never designed with ethanol in mind, so it may make a difference.

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From everything I learned about computer operation and tuning, ethanol is usable in any ODB2 vehicle (including VX). The injectors and fuel lines haven't been reported as degrading due to ethanol content either.

Though I originally had thought the difference was closer to 10%, materials I've read more recently suggest 5% increase in fuel usage should be expected when running E10 vs gasoline. Even IF closer to 10%, pure gasoline cost THAT much more too -- so there's no gain even if you can find/pay for it. Though it's nice to post numbers, it still hits the pocketbook about the same.

Finally, the O2 sensor is the primary component that IS designed to compensate for differences in fuels. It's "delta" changes with the change in fuel. It sees the need for more fuel and asks the ECM to provide it. Injector pulsewidth (PW) increases with the need for more fuel to get the burn back to a delta of "1". Where some talk about changing AFR from 14.7 to 14.1 that's just a starting point for most ECMs. Ultimately, the ECM is constantly monitoring for any changes in fuel -- whether crappy or E5, E10, or E15. It "knows" how to react by monitoring the O2 sensor.

Because there are limits, it takes a special system to handle something more extreme like E85. ECMs can only compensate so much. In the case of 1st generation ODB1 computers, the tolerance was +/-15%, giving a total "spread" of about 30%. OBD2 computers might be even wider.

I think I heard where they finally are realizing making fuel from corn is/was a bad idea. Seems I heard at least one state was considering LOWERING ethanol content. But, I didn't hear that first hand.

If you're driving a VX I doubt you're too concerned about pinching pennies on gas to begin with; personally I just like seeing how far I can stretch my tank.

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Originally Posted by vt_maverick

Also for anyone interested in oil consumption I burned a full quart on the way to Dayton but barely half a quart on the way back.

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...Darn....you were in Dayton.....

...you could have stopped by on your way down or up .....

...west chester is about 20-30 miles south of Dayton

Doh... sorry about that!