Why am I getting better mileage from regular fuel than premium?
12-23-2018, 05:39 AM
#1
Why am I getting better mileage from regular fuel than premium?
Hey 996 fans,
I make the same 40 mile drive to work every day (on the highway) and when using Premium Exxon fuel, I average 17 mpg. As an experiment, for three fill ups I put in regular Exxon fuel and am getting 19 mpg. Not only that but my 996 is driving just as good if not better on regular fuel than premium. How is this even possible?
Anybody else ever has this experience?
I make the same 40 mile drive to work every day (on the highway) and when using Premium Exxon fuel, I average 17 mpg. As an experiment, for three fill ups I put in regular Exxon fuel and am getting 19 mpg. Not only that but my 996 is driving just as good if not better on regular fuel than premium. How is this even possible?
Anybody else ever has this experience?
12-23-2018, 07:14 AM
#2
Drifting
Join Date: Sep 2011
Location: Ephrata, PA, USA now. Originally from the UK
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why would you even try a lower fuel than the octane level recommended by Porsche?????? If you are trying to get more mileage to save money then you should not be driving a Porsche.
12-23-2018, 08:54 AM
#3
Rennlist Member
Although I agree with you, I M CURIOUS AS TO WHY ALSO! I was putting 91 ethanol free in for a while since 93 was hard to find and I was always told the ethanol was not good for our engines. I was also told the 93 would give me better mileage so I go out of my way to put that in. It does not. I notice no difference at all...
12-23-2018, 09:12 AM
#4
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My guess is because the 91 octane you are using is not truly ethanol free, and the 87 that you experimented with does not contain as much ethanol, or any at all.
Regardless, your mpgs are not that great either way. Unless you are in a ton of stop & go traffic on you commute or hammer the car at every light and exit ramp?
Regardless, your mpgs are not that great either way. Unless you are in a ton of stop & go traffic on you commute or hammer the car at every light and exit ramp?
12-23-2018, 09:19 AM
#5
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Originally Posted by Dranon
Although I agree with you, I M CURIOUS AS TO WHY ALSO! I was putting 91 ethanol free in for a while since 93 was hard to find and I was always told the ethanol was not good for our engines. I was also told the 93 would give me better mileage so I go out of my way to put that in. It does not. I notice no difference at all...
If you want the best mpgs, go back to the 91 without corn.
If you are doing a track day, use the 93.
12-23-2018, 09:45 AM
#6
Hey 996 fans,
I make the same 40 mile drive to work every day (on the highway) and when using Premium Exxon fuel, I average 17 mpg. As an experiment, for three fill ups I put in regular Exxon fuel and am getting 19 mpg. Not only that but my 996 is driving just as good if not better on regular fuel than premium. How is this even possible?
Anybody else ever has this experience?
I make the same 40 mile drive to work every day (on the highway) and when using Premium Exxon fuel, I average 17 mpg. As an experiment, for three fill ups I put in regular Exxon fuel and am getting 19 mpg. Not only that but my 996 is driving just as good if not better on regular fuel than premium. How is this even possible?
Anybody else ever has this experience?
12-23-2018, 10:55 AM
#7
Rennlist Member
Saw a hottie filling up a 991 Turbo at Costco...with regular. I wanted to call her boyfriend and tell him to dump her. Don’t care what she looks like, that’s inexcusable!
TC
TC
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12-23-2018, 12:50 PM
#8
12-23-2018, 12:51 PM
#9
Rennlist Member
I suppose the OP is getting away with it, as noted (in a Mk2 Owner's manual): "Porsche also recognizes that these fuels [93 Octane] may not always be available. Be assured that your vehicle will operate properly on unleaded premium fuels with octane numbers of at least 95 RON (90 CLC or AKI). since the engine's 'Electronic Oktane TMknock control' will adapt the ignition timing, if necessary." The gas mileage is perhaps a tradeoff for performance.
12-23-2018, 01:14 PM
#10
To the root of the question, nominally higher octane fuels are less energy dense then lower ones. As a result, you need a higher volume for the same work. For reference, go dig into using E85 or Ethanol for drag or Indy (respectively). But that misses the benefits of higher-octane in that you can get higher total engine output because you can run higher compression and/or later timing. This is because they are less volatile. So your ECU retards the ignition and for very modest driving, it's barely noticeable. But you will also get no where near your peak power and you'll experience pre-detonation/knock at off-throttle and partial load. Go find a nice long hill you can run at a regular speed at partial throttle and compare the sound your engine makes between the two tanks. It's fairly obvious which sounds better.
12-23-2018, 01:33 PM
#11
Rennlist Member
To the root of the question, nominally higher octane fuels are less energy dense then lower ones. As a result, you need a higher volume for the same work. For reference, go dig into using E85 or Ethanol for drag or Indy (respectively). But that misses the benefits of higher-octane in that you can get higher total engine output because you can run higher compression and/or later timing. This is because they are less volatile. So your ECU retards the ignition and for very modest driving, it's barely noticeable. But you will also get no where near your peak power and you'll experience pre-detonation/knock at off-throttle and partial load. Go find a nice long hill you can run at a regular speed at partial throttle and compare the sound your engine makes between the two tanks. It's fairly obvious which sounds better.
This is the answer...
Alrhough, to the OP, just 2mpg difference (19 vs 17mpg), that’s too close to call, as the real world commute is always a little different every time, even if you try to make it as close as possible. Temperature differences, how people brake in front of you, etc. Too close to call. I’ve heard people claim the same 2mpg for different types of oil. Possible, sure, but not scientific.
Also, the idea that lower octane fuel is not suitable for an engine designed to run on higher octane depends on how you drive. Feathering the throttle and not using all available torque does not always have a negative effect - if at all. So if you are running across the flat country plains and want to cruise at 75mph on the open road, using about 50-60HP for that requirement, 91 or 89 octane is likely to have zero negative side effects. There are some fuels that have better fuel additives built-in to the higher octane, such as 92 or 93, and those additives are sometimes beneficial. But all else being equal, if your engine isn’t under load (high torque), there is no downside to lower octane. The people that say, “I’m paying for a high performance Porsche, why run low octane?” have a point, too, but again, depends on how you are driving and what your goals are.
12-23-2018, 02:04 PM
#12
Three Wheelin'
My guess is the ECU is adapting to the lower octane.
12-23-2018, 11:09 PM
#14
Rennlist Member
So since he owns a Porsche, he can't use his mind to do some testing and to learn about his car or try to save some money?
Do you happen to not travel around the world because you think the world is flat and you might fall off the edge?!!!
Kidding. I couldn't resist. lol
It's inexcusable for doing something you don't understand? lol
You can run 87 Octane in the 991 Turbo. You just won't get optimum performance out of it. It doesn't hurt the engine though.
I've noticed many people over the years not realizing how much technology has changed. Cars have MANY more sensors now and are controlled by pretty advanced computers. If the knock sensor senses a knock, it will adjust the timing accordingly.
This technology has been around since at least 2001. I bought a 2001 325ci and did some research back then. I learned that the computer will simply adjust the timing if you run lower octane. I've been running 87 octane for 18 years this coming Feb. No issues at all. Plus, I have a lot more cash in my pocket from not paying for premium gas.
Do you happen to not travel around the world because you think the world is flat and you might fall off the edge?!!!
Kidding. I couldn't resist. lol
It's inexcusable for doing something you don't understand? lol
You can run 87 Octane in the 991 Turbo. You just won't get optimum performance out of it. It doesn't hurt the engine though.
I've noticed many people over the years not realizing how much technology has changed. Cars have MANY more sensors now and are controlled by pretty advanced computers. If the knock sensor senses a knock, it will adjust the timing accordingly.
This technology has been around since at least 2001. I bought a 2001 325ci and did some research back then. I learned that the computer will simply adjust the timing if you run lower octane. I've been running 87 octane for 18 years this coming Feb. No issues at all. Plus, I have a lot more cash in my pocket from not paying for premium gas.
TC
