# New owner... need help with octane



## pilot_corey (Mar 24, 2011)

Hi all, 

I just bought a new Golf MkVI (the 2.5 V5 manual) last week and it is time for my first fill-up. The dealer told me I may want to use mid-grade fuel. I live in Denver, so because of the altitude the octane ratings are 85, 87, 91. I filled up with 87, but I am wondering if there is any reason to use 91? I see a lot of threads on octane, but each one I read deals with the GTI or a chipped/modded engine. So, what octane should I use for the standard engine? I don't want to throw away money, but I also want to do whats best for the engine. 

Thanks in advance for the help!


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## seanmcd72 (May 14, 2008)

You are going to get every single answer on this one. All it needs is 87. For 45K miles I've been unable to bring myself to use 87, but for the last three tanks I have and it's perfectly fine. I am a lot closer to sea level than you are but I say try 87 for a while, then try 91 and compare notes.


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## HIBB 304 (Nov 8, 2008)

pilot_corey said:


> Hi all,
> 
> I just bought a new Golf MkVI (the 2.5 I5 manual) QUOTE]
> 
> Fixed it for ya.:laugh:


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## kungfoojesus (Jan 10, 2005)

If you log your mileage you will probably have similar results as I did. The 93 octane out here doesn't actually cost me much more if anything at all. I get another 20-30 miles to the tank and spend a net difference of less than a couple $ per fill up. Well worth it to me. 

Log your mileage and see what happens. Also, I was getting faults when running 87 octane due to predetonation (pinging). My 09 has the same engine management as your 2010, older 2.5's had different so your results won't exactly follow what most people here state. 

Also, try to find out what fill stations in your area sell tier 1 gasoline. This will make a big difference as well. Go to the busiest one on your daily routes to avoid water in the gas as well. Higher volume usually gets you better gas than anything but all else equal go for the tier 1 stations 89 octane or higher in my opinion. 

Keep in mind, especially this time of year, that tire pressure will really throw off your gas mileage logs so I would log at least 3 tanks of each and average them out before assuming one is better than the other. 

Why couldn't you be cool like everyone else in CO and just buy a smug little prius? hehe j/k Gratz on the new VW you'll love it. If anyone gives you stuff for not buying a prius like half your neighbors, just inform them VW actually built the first hybrid back in the 1980's... and that their prius pollutes more than a land rover if you add up the manufacturing cost of their 1,000lb battery. 

Good luck.


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## bunnyfufu (Jan 25, 2011)

i ran 87 for the first two weeks i owned my car and then tried 93 and have used that ever since(now i have to due to being chipped)the car will get better mpg and feel more responsive.also i feel beter now that i know my engine is getting the best.its kinda like eating mcdonalds one day and then eating a home cooked meal.


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## pilot_corey (Mar 24, 2011)

kungfoojesus said:


> If you log your mileage you will probably have similar results as I did. The 93 octane out here doesn't actually cost me much more if anything at all. I get another 20-30 miles to the tank and spend a net difference of less than a couple $ per fill up. Well worth it to me.
> 
> Log your mileage and see what happens. Also, I was getting faults when running 87 octane due to predetonation (pinging). My 09 has the same engine management as your 2010, older 2.5's had different so your results won't exactly follow what most people here state.
> 
> ...


 Before I had been driving a 4.7 liter Duragno, so you can imagine the looks I would get from the Prius drivers when I would pull up to a light! 

Thanks for the help everyone. I will average out my mileage and see what I get. I am avoiding the Safeway/grocery store brand gas for this car, and going to the Shell station instead. Looking at the price difference between the two grades, the cost is not that much more, and if it is better for the engine, I will happily pay the extra few bucks.


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## TylerO28 (Jul 7, 2008)

Premium only

As high as you can get
Car runs so much better

And in the end its a couple bucks.
Just do it your new motor will thank you

Think if it like this more octane equals more compression needed and less ping problems

Keep those new rings fresh and motor running like new

The fsi and tsi motors CAN run on low octane but good god why? Less power less mileage

Look up european car magazine they tested the 2.5 with both low and high octane. The result was crazy! More power better mileage and smother idle.

Just go 91 to 93 and be done
/thread


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## LampyB (Apr 2, 2007)

I live in Denver too, and up until a few weeks ago my rabbit was completely stock. When running 91 the car felt faster, but for over a year i ran only 87 for economical purposes. Car ran completely fine, it says 87 inside of the gas cap so you'll be completely fine. It isn't worth putting 91 in the car every time, only once in a while to possibly clean out the fuel system a bit. The price of 91 in Colorado is high enough to where it didn't make any sense for me to use it regularly. And I definitely agree with only using tier 1 gas stations...conoco, shell, etc. 

People will argue this until they turn blue in the face, but if VW recommends 87 and above, using 87 is perfectly ok. I didn't see better mileage when using 91, it actually got worse because the car drove a bit quicker so my foot was heavier.


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## TrillyPop (Jan 27, 2010)

When my car was stock w/intake and pulleys only, I used 87 for one tank then switched to 91. The car had better character with 91, smoother idle, and felt like a little more power per butt dyno. Have never looked back


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## phukenvr6 (Mar 11, 2009)

Ive been using 87 for a few months but switched to 93 the last couple weeks. I have noticed my shifts (auto 6spd) have been smoother and better response from take off. I won't be switching back for the extra 2 bucks per fill. 


Sent from my iPhone using Tapatalk


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## jettafan[atic] (Dec 2, 2008)

kungfoojesus said:


> If anyone gives you stuff for not buying a prius like half your neighbors, just inform them VW actually built the first hybrid back in the 1980's... and that their prius pollutes more than a land rover if you add up the manufacturing cost of their 1,000lb battery.


 It's also worth noting that the 2.5 cars are either ultra low emissions vehicles (ULEV) or partial zero emissions vehicles (PZEV) so in a lot of cases the air going out of our (stock) exhaust is cleaner than the air the car sucks in. Kind of like a rolling carbon footprint reduction. 

On to the actual topic, octane is one of those things that can be highly debated for days and there's a lot of misinformation about it. Octane is really simple, it is just the rating of a fuels ability to resist preignition. Higher octane fuel will of course resist preignition better than lower octane fuel so essentially you can either squeeze more air/fuel in or squeeze the AF mixture more and it wont combust before the spark. 

If your engine is rated for 87 octane then you do not need to use any more, it will not knock/detonate/preignite on 87 octane. Any fuel with a given octane rating is not necessarily "cleaner" than any other octane rating, it just wont combust at the same point. Now you're gonna have a lot of people telling you how much better their car runs on higher octane and there's been hundreds if not thousands of magazine articles detailing how much better higher octane is for your car. Some articles I've seen quoting gains as high as 18% more hp or tq or mileage and there's a kernel of truth there but a lot more sensationalism. 

This is the bottom line, higher octane can lead to producing more power, much more under the perfect circumstances actually. In order for an engine to take advantage of higher octane it needs to be tuned for it, the stock tune on our cars will accomodate slightly for higher octane fuel but it's not much. Higher octane allows for a lot of things like advancing timing and higher compression ratios and forced induction to make more power but using a higher octane fuel does not automatically = more power.


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## kungfoojesus (Jan 10, 2005)

jettafan[atic] said:


> This is the bottom line, higher octane can lead to producing more power, much more under the perfect circumstances actually. In order for an engine to take advantage of higher octane it needs to be tuned for it, the stock tune on our cars will accomodate slightly for higher octane fuel but it's not much. Higher octane allows for a lot of things like advancing timing and higher compression ratios and forced induction to make more power but using a higher octane fuel does not automatically = more power.


 Again, like I stated earlier, the newer engine management in the 09+ 2.5's will very easily make use of 93 octane fuel. Don't pay attention to the older vehicles that claim you need a chip. There are plenty of dyno's out there showing that a stock motor running the siemens engine management (09+ that doesn't have a MAF) makes great deal better torque and power on higher octane. 

Further more, my motor was pinging on 87 octane fuel. The faults were recorded in the ECM and showed via vag com. It says 87 octane on my gas lid but in reality this was a scam by VW to make the cost of ownership look lower than it really is. If you run the low octane stuff on the 09+ its the same as running a pre 09 unchipped, tons of flat spots and horrible low end torque and tons of timing pulled. Your 09+ WILL pull timing if you don't run higher than 87 octane. 

Night and day difference below 2k for me between 93 and 87 octane, also around 4k and pulls harder to 6k, easier to pass in 5th at about 55-60mpg... big difference. My wife filled my car up a few times with varying octane fuel and I told her if it was 87 or 93 every time except once. We had an argument about me wasting my $$$ but I proved her wrong. If the butt dyno is that accurate then I know its worth paying $$$ for it. Again, was recording faults in my 09+ on low octane fuel according to my car as well.


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## thygreyt (Jun 7, 2009)

kungfoojesus said:


> Again, was recording faults in my 09+ on low octane fuel according to my car as well.


 same on my 09. 
if i use 87 the car runs like crap.


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## cryption (Mar 28, 2006)

My 09 has 56k miles on it. I run any of the 3 octanes, depending on the price spread. If it's 10 cents between grades I'll run premium .. but I drop grades the larger the spread. I can never really tell a difference. 

2.0t only got Premium, however.


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## jettafan[atic] (Dec 2, 2008)

That's interesting, I wasn't aware the 09's were pinging on 87 or that the stock tune on the 09's really accomodated higher octanes that much. Do you know how much it will advance or retard the timing?


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## seanmcd72 (May 14, 2008)

something is wrong if you are pinging with 87


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## jettafan[atic] (Dec 2, 2008)

seanmcd72 said:


> something is wrong if you are pinging with 87


That's what I was thinking, even with the 09's having a different tune it's pretty hard to believe that the tune would be causing preignition. Have there been any TSBs for it? If it's the tune they switched to then it should be an issue coming up on most of the 09+ 2.5s and to the best of my knowledge that's the sort of thing that pretty much always gets either a TSB or recall for a reflash. 



kungfoojesus said:


> in reality this was a scam by VW to make the cost of ownership look lower than it really is. If you run the low octane stuff on the 09+ its the same as running a pre 09 unchipped, tons of flat spots and horrible low end torque and tons of timing pulled.


I was thinking about this some more and I really doubt that it would be a scam by vw to make the cost of ownership look lower than it should be. The impact of having to use 89 as opposed to 87 would be negligible compared to the costs of potential problems caused by engine knock. I don't know enough about the 09s to really point in an accurate direction but I would be looking for anything causing hot spots. Any carbon deposits on valves or plugs, any imperfections in cylinder walls, sticky lifters causing fouling from carbon, etc...


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