MPG Testing AR-5 + 93 Octane

[vt_maverick]

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. )



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



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.)




Price and quantity at the pump:



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.

[Marlin]

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)

[eternal21]

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.

[vt_maverick]

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.

[vt_maverick]

Chris what time of year was your trip?

[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.

[tom4bren]

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.

[Marlin]

It was 27DEC

[eternal21]

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.

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.

[tom4bren]

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

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.

[eternal21]

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.

+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*

[tom4bren]

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.

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.

[eternal21]

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.

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

[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.

[tom4bren]

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.

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.