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Running premium fuel in older vehicles?


erathge
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So today I was with a friend picking up his 01' Highlander (295,000 Kilometres) from the Toyota dealership. The service guy stated that the cat was starting to get a little clogged up and that he should consider running a high grade fuel, specifically Chevron 94 octane. He then went on to say that he runs 94 in his own 2001 Pathfinder and that I should consider running it too (I have 290,000 Kilometres). He said he highly recommends running high octane fuel in older vehicles. The funny thing is, I have read before from other sources that there isn't really a point to run a higher octane in an engine like the vg33. I don't think I could afford to pay around 20 cents/litre more for premium...

 

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Edited by erathge
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You're right, there is no point in running on premium as far as I can tell. I tried a couple of tank fulls in my truck & the only difference it made was to my wallet :laugh:

 

These vehicles are designed to run on regular so that's what I use. Now my buddy's LR3 is a different story, that's made to run on premium so no way I'm getting an LR3 that also only does about 12mpg :thumbsdown::ohno01:

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This is one of those things that are a never ending battle. If you keep track of your gas mileage like I do you can try it out and see if there is a difference. I personally always go to the same gas station. A chevron. I also only run premium. Now I am sure I am gonna get a few people on here that say "oh thats just dumb"! Well I get 2mpg better on premium. I have tested it back and forth. I went down to E and put a tank of regular in. Well I could tell a difference right off the bat. I was only getting 13-14 with regular 87 octane. With premium I could get almost 18 sometimes. And no I didnt do anything different on the 87 octane. Same driving everyday. I have a 98 with almost 199850 miles. So like I said just try it. Or track a few of your fill ups and then switch. I calculated out that the extra 3-4 dollars a tank is saving me about 10 bucks a tank because of the because mileage.

 

Just my experience.

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I've seen a similar difference in my 1.6L Miata. At least I'll keep telling myself that as it is my "baby". The Pathy is for weekend runs to the dump, trail riding, and multi-peeps hauling around town .. shoot, might as well throw in a tailgate excursion or five during fooseball season. I'll just keep with Town's "don't waste my $" attitude with La Blanca.

Edited by devonianwalk
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The grade of fuel you run depends on your engine's compression ratio. For example, VG engines in Pathfinders are designed to run on regular 87. They do not have a map for premium fuel and while it will work you will not notice any difference. VQs on the other hand are made for Premium fuel.

 

That Highlander is probably made for regular so unless it says Premium is recommended, run it on regular. The catalytic converter failing has nothing to do with the grade of gas you run.

Edited by Tungsten
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This is one of those things that are a never ending battle. If you keep track of your gas mileage like I do you can try it out and see if there is a difference. I personally always go to the same gas station. A chevron. I also only run premium. Now I am sure I am gonna get a few people on here that say "oh thats just dumb"! Well I get 2mpg better on premium. I have tested it back and forth. I went down to E and put a tank of regular in. Well I could tell a difference right off the bat. I was only getting 13-14 with regular 87 octane. With premium I could get almost 18 sometimes. And no I didnt do anything different on the 87 octane. Same driving everyday. I have a 98 with almost 199850 miles. So like I said just try it. Or track a few of your fill ups and then switch. I calculated out that the extra 3-4 dollars a tank is saving me about 10 bucks a tank because of the because mileage.

 

Just my experience.

 

Interesting stuff. I was wondering if the extra cost was offset by the better mileage.

 

I know when I put premium in my wife's old 1995 Corolla it seemed to run better, but not sure if it made any difference mileage wise. Never noticed any difference with the Pathy performance wise & again I wasn't checking the mileage either.

 

The better mileage you're getting is great, whatever works for you I guess.

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Well I just use an app on my phone to keep track. Been tracking for like 3 years. You always know there is something wrong when you start getting worse gas mileage. I have always ran premium from my 300zx turbo to my 05 spec V to the pathfinder. Given the first two do ask for it. Anyway I had a fellow mechanic friend with me when I was getting gas in my pathy one day and of coarse noticed I was putting premium in it. Well so I bet him 20 bucks that I was getting better mileage and guess what? He paid for the next tank. HAHA Maybe its just the extra additives in the premiums at Chevron?

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Like I said its just what happens to me at my gas station. Would be kinda cool to do an actual study. Go around to different gas stations and try all three octanes. Just to see what happens.

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Simply put Octane is Resistance to Detonation. Premium does not make more power or burn cleaner its just more resistant to detonation.


One characteristic of resisting detonation is that the fuel burns slower. This is not an issue in higer compression engines because the Compression acclerates the flame front. But in engines designed for low octane the fuel does not burn as fast and sometimes you wind up with MORE unburnt fuel.

Unburnt fuel (hydrocarbons) means more work for catalytic converters to remove. So really, the service guy is mistaken.

 

Premium tune? Basically if the engine is the same but the Tune is different. (pathfinder vs M30) the octane optimization has been made via changing the timing curve and modifying the fuel maps a based on how much of that specific fuel will or will not burn at a given engine condition.

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Thanks for everyones input so far, it sounds like I'll be sticking to regular. I just wanted to see what everyone thought about this, as I was a bit surprised when I heard the service guy saying these things. However, I might try a tank or two of premium and see if I notice a difference in MPG.

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Premium tune? Basically if the engine is the same but the Tune is different. (pathfinder vs M30) the octane optimization has been made via changing the timing curve and modifying the fuel maps a based on how much of that specific fuel will or will not burn at a given engine condition.

 

This is true, you can advance the timing enough to actually run higher octane fuel. You might be able to get a mpg boost from this because of more compression happening before ignition. No idea if 96+ VG powered Pathfinders do this though. I know the older ones don't.

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It could be the fact that they put less ethanol into premium fuel than into regular. I don't know how that works but that's what I'm guessing.

 

IMHO, this is most likely the reason for the mpg boost. I know the Shell gas I put in (91 octane) does not have any added ethanol, whereas the mid-grade and regular do. With the government push for more fuel efficient vehicles, you'd think they would stop putting ethanol in all blends just for the efficiency gains. I personally HATE ethanol for passenger vehicles.

 

Ethanol has a lower energy content (about 1.5 gallons of ethanol = 1 gallon of gasoline) so you get less power output from ethanol blends, which would result in worse fuel efficiency.

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Now put elevation into the equation:
Less octane is required at elevation because at higher elevations there is less barametric pressure. Standard pressure is 14.6 psi at sea level, around 11k feet that is closer to 10 psi. As elevation goes up, pressure goes down.

So your motor has less compression at say 10k feet than it does at sea level, everything else equal. At higher elevation since you do not have the compression you have at sea level you do not need as much octane to prevent (pre) detonation.

Of course this is also the same reason you can get a higher compression head for higher elevations than lower elevations. You are really just compensating for what you already lost with the elevation gain. As you increase cylinder head compression you need more octane.

At elevation you need less octane on a stock motor than you do on the SAME stock motor at sea level. Now if you increase the compression on that motor you will need more octane.
I live at 7000', most normal cars will not last any longer or preform any better with a higher octane than 87."
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i dont think i have less low end power than a vg at all i have owned a vg powered hardbody 2wd and with a 80k miles vs. my pathys 1/4mile time was about .5 of a second faster with similar reaction times. And one of my goodfriends that has a frontier supercharged barely can beat mine off the line and i always win when we race i just dont think to say that a vq has less low end torque is valid bigger engie more cams more valves ususally equalls more power throughout the entire power low and high just saying

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Octane never made any difference in my mileage/performance when I used to keep track, but what station I use for fuel does. Not so much the brand either, theres 1 pacific BP (sadly the closest fuel station to me) that I get horrible mileage out of no matter what vehicle it goes into (and their diesel always kicks on the "water in fuel" light on our diesels at work, I've called their customer complaint line multiple times) and the private owned fuel station that is second closest to me seems to last the longest (and is the cheapest priced, your in the immediate Pgh area and need fuel-stop at Kress Service right off of route 28! :aok: )

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i dont think i have less low end power than a vg at all i have owned a vg powered hardbody 2wd and with a 80k miles vs. my pathys 1/4mile time was about .5 of a second faster with similar reaction times. And one of my goodfriends that has a frontier supercharged barely can beat mine off the line and i always win when we race i just dont think to say that a vq has less low end torque is valid bigger engie more cams more valves ususally equalls more power throughout the entire power low and high just saying

 

VQ wins for overall power hands down but the VG is a more suitable engine for cruising because it makes good torque where the gearing is for cruising. The VQ starts to become efficient at 2500 rpm where the VG starts to become efficient at about 1500 rpm. Since both trucks share the same transmission and final drive, they have the same gearing. The permanently locked front axle on the R50s could also contribute to the drop in MPGs. More displacement could also be a factor but the VQ is DOHC so it's embarrassing.

Edited by Tungsten
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i dont trust epa standards at all but just throwing it out there i kind of dont buy it.

 

http://www.fueleconomy.gov/feg/Find.do?action=sbs&id=18226&id=13198&id=12451

 

i mean i know with good driving i can average 16 in the city i can see a vg averaging the same but not better

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I am currently averaging 18.5 mpg with my VG30E on regular gas with the ethanol crap in it but everyone I talk to who has an R50 with the VQ35DE only averages something like 14 mpg. That's about as typical as a V8 truck. :lol:

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