Octane query (no, not the same old about using el cheapo)
12-10-2004, 06:58 AM
#1
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Octane query (no, not the same old about using el cheapo)
Here's a different octane-related question.
On Monday I stopped at a Sunoco out at Fairfax Circle because I was low on gas, it's the cheapest around except for the no-names, and I wanted to see how the TL liked their 94 octane. I was surprised to find that they no longer sell the 94. Instead, they now have 87, 89, 91, and 93. This is the first place I have ever seen 91 octane gasoline. I know they have it out west, but I have never seen it anywhere on the East Coast or in eastern Canada. Every other station in the DC area sells 87, 89, and 93 (many used to sell 92 instead of 93, but 93 has become standard in the past 8 to 10 years). I filled up with the 93.
So my question is this--do cars develop a "tolerance" for the octane you normally feed them? Kind of like how if you consistently drink a lot, you develop a tolerance for booze and it takes more to get you smashed. In other words--the TL's owner's manual says "91 or higher." Given that 91 is not generally available around here, I use what is--i.e., 93. I briefly considered whether to put in 91 on Monday, but I went ahead and used the 93 because (1) it was only 3¢ a gallon more than 91 and (2) I wasn't sure if the car is now "used to" 93 and wouldn't like the 91. (I suppose after only 5200 miles it is likely too soon for that.)
What prompts me to wonder about this is that I remember that when my father bought a 1982 Accord as a new car, the only grades of unleaded gas were 87 and 92 (this was prior to the phase-out of leaded) and it never ran quite right on 87 for whatever reason. For a while he mixed grades, but then when they went to the electronic pumps he switched to straight 92. Once they came out with middle-grade unleaded we tried that and it never worked as well either, so we always figured that the engine was used to the 92 octane.
Anyone have any thoughts? As a practical matter I would not be using the Sunoco 91 on a regular basis since the only Sunoco near my house/commute was closed for a road-widening project.
On Monday I stopped at a Sunoco out at Fairfax Circle because I was low on gas, it's the cheapest around except for the no-names, and I wanted to see how the TL liked their 94 octane. I was surprised to find that they no longer sell the 94. Instead, they now have 87, 89, 91, and 93. This is the first place I have ever seen 91 octane gasoline. I know they have it out west, but I have never seen it anywhere on the East Coast or in eastern Canada. Every other station in the DC area sells 87, 89, and 93 (many used to sell 92 instead of 93, but 93 has become standard in the past 8 to 10 years). I filled up with the 93.
So my question is this--do cars develop a "tolerance" for the octane you normally feed them? Kind of like how if you consistently drink a lot, you develop a tolerance for booze and it takes more to get you smashed. In other words--the TL's owner's manual says "91 or higher." Given that 91 is not generally available around here, I use what is--i.e., 93. I briefly considered whether to put in 91 on Monday, but I went ahead and used the 93 because (1) it was only 3¢ a gallon more than 91 and (2) I wasn't sure if the car is now "used to" 93 and wouldn't like the 91. (I suppose after only 5200 miles it is likely too soon for that.)
What prompts me to wonder about this is that I remember that when my father bought a 1982 Accord as a new car, the only grades of unleaded gas were 87 and 92 (this was prior to the phase-out of leaded) and it never ran quite right on 87 for whatever reason. For a while he mixed grades, but then when they went to the electronic pumps he switched to straight 92. Once they came out with middle-grade unleaded we tried that and it never worked as well either, so we always figured that the engine was used to the 92 octane.
Anyone have any thoughts? As a practical matter I would not be using the Sunoco 91 on a regular basis since the only Sunoco near my house/commute was closed for a road-widening project.
12-10-2004, 07:39 AM
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FWIW, I filled up my TL on Sunoco 91 yesterday in Towson, MD, must be a Sunoco thing. Most all newer cars will not benefit from anything higher than the manufacturer's recommendation (aside from those equipped certain aftermarket performance parts). Putting 93 in a car that only needs 87 is a waste of money, same thing for putting 93 in a car that requires 91. I only put 87 in my old Jeep and my Talon gets 116 octane leaded gas regularly 
and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
12-10-2004, 08:00 AM
#3
Originally Posted by boosteddsm
FWIW, I filled up my TL on Sunoco 91 yesterday in Towson, MD, must be a Sunoco thing. Most all newer cars will not benefit from anything higher than the manufacturer's recommendation (aside from those equipped certain aftermarket performance parts). Putting 93 in a car that only needs 87 is a waste of money, same thing for putting 93 in a car that requires 91. I only put 87 in my old Jeep and my Talon gets 116 octane leaded gas regularly and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
12-10-2004, 08:52 AM
#4
Octane tolerance..
Vehicles don't develop a tolerance to octane, but, depending on how clean or dirty the combustion chamber is, they can develop a need for higher octane.
Build up in the chamber can increase compression and cause predetonation. The resolution is to either pull the heads and have the deposits cleaned out or use higher octane fuel.
I don't think this problem is as common as it used to be, but can happen after a long period of time.
The change in octane you see may have to do with refinery capacity or a decision to reformulate their fuels since 94 octane isn't needed by that many cars - a purely marketing driven decision.
Using more than the recommend 91 is a waste of money, it won't improve the performance of car. Using less than 91 will result in poorer performance.
Build up in the chamber can increase compression and cause predetonation. The resolution is to either pull the heads and have the deposits cleaned out or use higher octane fuel.
I don't think this problem is as common as it used to be, but can happen after a long period of time.
The change in octane you see may have to do with refinery capacity or a decision to reformulate their fuels since 94 octane isn't needed by that many cars - a purely marketing driven decision.
Using more than the recommend 91 is a waste of money, it won't improve the performance of car. Using less than 91 will result in poorer performance.
12-10-2004, 09:08 AM
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Sunoco is having to cut 94 in many markets because of anti-MTBE regulations. This is the first I've heard of a state south of PA having 94 cut, but I know that many of the northern states have already had it disappear.
Everyone wondering about this read the above twice-- it's right on target.
And Nice DSM, BoostedDSM!, I've always loved those cars.
Scott
Originally Posted by boosteddsm
FWIW, I filled up my TL on Sunoco 91 yesterday in Towson, MD, must be a Sunoco thing. Most all newer cars will not benefit from anything higher than the manufacturer's recommendation (aside from those equipped certain aftermarket performance parts). Putting 93 in a car that only needs 87 is a waste of money, same thing for putting 93 in a car that requires 91. I only put 87 in my old Jeep and my Talon gets 116 octane leaded gas regularly and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.And Nice DSM, BoostedDSM!, I've always loved those cars.
Scott
12-10-2004, 09:28 AM
#6
Three Wheelin'
Here in central FL we can only get 87, 89, and 93 octane. I use 93 but I would use 91 if it were available. However, I can go two counties over from us and they sell 91 there. I don't get it unless individual counties stipulate what octanes to sell.
12-10-2004, 09:29 AM
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Originally Posted by Scott GN231
Sunoco is having to cut 94 in many markets because of anti-MTBE regulations. This is the first I've heard of a state south of PA having 94 cut, but I know that many of the northern states have already had it disappear.
I was a little disappointed to see the 94 go, though, because I occasionally drive my brother's 1974 Beetle and that car seems to love the higher-grade stuff. Maybe it's the issue kosh2258 raises.
Thanks, guys. I may try the 91 next time I need gas and there's a Sunoco around. I don't think it's worth driving out of the way just to get the 91 instead of ordinary 93, though. It seems like a more of a waste of money to drive 10 miles out of the way just to get 91 octane than it would be to spend 3¢ a gallon more on the generally-available 93 octane. If 91 were to become more common, I suppose then I would try switching.
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12-10-2004, 01:02 PM
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Ya I was choked when ESSO stopped using 92 octane, and now use 91 octane.. This was the reason I chose esso... same gas price, better octane levels... . argh.. anyways, they are now 91 for supreme 
.
I have also heard many things that the vehicles that you drive DO get 'used to' a specific gas that you run through... even the different brands, not even looking at the same company dif octane... I know that a lot of gas comes from the same place, but each gas has different attributes to it, and changing gas stations all the time is not the best for the engine.. any1 confirm or dispute this?
.I have also heard many things that the vehicles that you drive DO get 'used to' a specific gas that you run through... even the different brands, not even looking at the same company dif octane... I know that a lot of gas comes from the same place, but each gas has different attributes to it, and changing gas stations all the time is not the best for the engine.. any1 confirm or dispute this?
12-10-2004, 01:31 PM
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Originally Posted by Scott GN231
And Nice DSM, BoostedDSM!, I've always loved those cars. Scott
12-10-2004, 05:58 PM
#10
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While engines cannot develop a tolerance for a particular fuel type, they can do something which would seem to someone that this is the case.
If you have a car with, say, an 8.8:1 mechanical compression ratio that is designed to burn 87 octane fuel and you start using 93 octane, several things will happen. Your engine will produce a higher level of emissions. You fuel economy will drop a little. And your engine will produce less power.. for a while.
I say for a while because of the fact that less of the higher octane fuel will be burned in the combustion chamber and this will create more carbon deposits. These deposits will adhere to the tops of the pistons, the head, and the valve faces. And this will raise your mechanical compression ratio which will then require a higher octane fuel to be used.
If you have a car with, say, an 8.8:1 mechanical compression ratio that is designed to burn 87 octane fuel and you start using 93 octane, several things will happen. Your engine will produce a higher level of emissions. You fuel economy will drop a little. And your engine will produce less power.. for a while.
I say for a while because of the fact that less of the higher octane fuel will be burned in the combustion chamber and this will create more carbon deposits. These deposits will adhere to the tops of the pistons, the head, and the valve faces. And this will raise your mechanical compression ratio which will then require a higher octane fuel to be used.
12-10-2004, 08:02 PM
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I wonder how accurate, generally, the posted octane ratings are on the pump at any station. I sorta never trust that its "policed" properly and probably are not accurate. There are not enough inspectors to even police the policy and i'm sure many gas stations know it and we probably are not getting the exact octane rating that is posted. I had a friend that worked at Mobil and he said he heard the owner had mixed the delivery in different tanks many times, and said he could always say it was an error if it was ever evaluated. Has anyone sent out a sample to a laboratory for independent testing lately?
12-11-2004, 05:55 PM
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Originally Posted by boosteddsm
FWIW, I filled up my TL on Sunoco 91 yesterday in Towson, MD, must be a Sunoco thing. Most all newer cars will not benefit from anything higher than the manufacturer's recommendation (aside from those equipped certain aftermarket performance parts). Putting 93 in a car that only needs 87 is a waste of money, same thing for putting 93 in a car that requires 91. I only put 87 in my old Jeep and my Talon gets 116 octane leaded gas regularly and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
and of course my week old TL gets 91 or higher. Oh, and cars won't "adapt" to a particular octane reading.
12-11-2004, 05:56 PM
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Originally Posted by SouthernBoy
While engines cannot develop a tolerance for a particular fuel type, they can do something which would seem to someone that this is the case.
If you have a car with, say, an 8.8:1 mechanical compression ratio that is designed to burn 87 octane fuel and you start using 93 octane, several things will happen. Your engine will produce a higher level of emissions. You fuel economy will drop a little. And your engine will produce less power.. for a while.
I say for a while because of the fact that less of the higher octane fuel will be burned in the combustion chamber and this will create more carbon deposits. These deposits will adhere to the tops of the pistons, the head, and the valve faces. And this will raise your mechanical compression ratio which will then require a higher octane fuel to be used.
If you have a car with, say, an 8.8:1 mechanical compression ratio that is designed to burn 87 octane fuel and you start using 93 octane, several things will happen. Your engine will produce a higher level of emissions. You fuel economy will drop a little. And your engine will produce less power.. for a while.
I say for a while because of the fact that less of the higher octane fuel will be burned in the combustion chamber and this will create more carbon deposits. These deposits will adhere to the tops of the pistons, the head, and the valve faces. And this will raise your mechanical compression ratio which will then require a higher octane fuel to be used.
12-11-2004, 06:00 PM
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Originally Posted by Nicki
I wonder how accurate, generally, the posted octane ratings are on the pump at any station. I sorta never trust that its "policed" properly and probably are not accurate. There are not enough inspectors to even police the policy and i'm sure many gas stations know it and we probably are not getting the exact octane rating that is posted. I had a friend that worked at Mobil and he said he heard the owner had mixed the delivery in different tanks many times, and said he could always say it was an error if it was ever evaluated. Has anyone sent out a sample to a laboratory for independent testing lately?
12-11-2004, 11:01 PM
#15
Ex-Acura Service Manager
There are a few upper engine carbon removal solutions out there that do a very effective job at cleaning soft carbon deposits from valves, combustion chambers & intake tracts.
Back in the late 80s & early 90s, not long after the elimination of leaded fuels, soft carbon buildup was a scourge for many manufacturers. Cars would sometimes crank over & not start, or develope pre-ignition on acceleration. Some makers went as far as removing cylinder heads & valves to clean the soot off of them. Many manufacturers didn't cover this under warranty, because it was due to a naturally occuring process of burning fossil fuel.
Necessity is the mother of invention, so now there are wonderful products out there to keep this sort of thing to a minimum.
Back in the late 80s & early 90s, not long after the elimination of leaded fuels, soft carbon buildup was a scourge for many manufacturers. Cars would sometimes crank over & not start, or develope pre-ignition on acceleration. Some makers went as far as removing cylinder heads & valves to clean the soot off of them. Many manufacturers didn't cover this under warranty, because it was due to a naturally occuring process of burning fossil fuel.
Necessity is the mother of invention, so now there are wonderful products out there to keep this sort of thing to a minimum.
12-12-2004, 09:12 AM
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To Bluenote;
Yep. We have a superb shop here in my little town in western Prince William County, VA, owned by a mechanic who is not only outstanding, but honest and great to work with. He has more business than he can handle and has customers even coming over from Maryland to avail themselves of his sevice.. he's that good.
He treated my wife's '96 BMW 328i to an engine purge (not BG, by the way) and a mess of crap came out of the thing. And what an improvement in the engine.
Anyway, for you people who might live in Virginia close to my area who may want to check out this man's place, send me a PM and I'll be happy to give you the info.
Yep. We have a superb shop here in my little town in western Prince William County, VA, owned by a mechanic who is not only outstanding, but honest and great to work with. He has more business than he can handle and has customers even coming over from Maryland to avail themselves of his sevice.. he's that good.
He treated my wife's '96 BMW 328i to an engine purge (not BG, by the way) and a mess of crap came out of the thing. And what an improvement in the engine.
Anyway, for you people who might live in Virginia close to my area who may want to check out this man's place, send me a PM and I'll be happy to give you the info.
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