Deciphering fuel octane at higher altitude
November 3, 2014 11:30 AM Subscribe
We just ordered a new vehicle (Volvo V60 with a 4-cylinder turbocharged engine) and I'm trying to figure out the minimum grade of fuel to use. The owner's manual says "Volvo recommends premium fuel for best performance, but using 87 octane or above will not affect engine reliability." In most places in the US, that's regular grade fuel, but we're at higher altitude in New Mexico where regular is 86. If we wanted to meet Volvo's minimum, would that be midgrade 88 to hit that minimum or would regular 86 still meet that spec since we're at higher altitude? Googling returns every answer under the sun, which may be the case here? We'll ask the dealership when it arrives. Thanks!
I previously owned a Volvo V70 T5. I had historically been a "cheapest gas I can find" driver, but the V70 was rated for premium gas - and indeed, performance of the high-pressure turbo in the V70 would really suffer when I would occasionally forget and fill it with standard-grade gas. (I wouldn't realize that I filled it with regular while standing at the pump - it would come to haunt me a few days later with diminished performance.)
Please do check with the dealership, but I don't think you're going to kill that car with 86, especially since it doesn't look like a high-pressure turbo in that car. The question will be whether or not it's enjoyable to drive with 86, and I think that'll end up being an experiment at the pump.
posted by eschatfische at 12:27 PM on November 3, 2014
Please do check with the dealership, but I don't think you're going to kill that car with 86, especially since it doesn't look like a high-pressure turbo in that car. The question will be whether or not it's enjoyable to drive with 86, and I think that'll end up being an experiment at the pump.
posted by eschatfische at 12:27 PM on November 3, 2014
The gas stations are selling lower-octane gas at altitude because the 'thinner' air means that your car is basically running at a reduced compression level already. Someone determined at some point that 86 octane at that altitude is functionally equivalent to 87 at a lower altitude, and there's no reason not to believe them.
Even if you were to fill up with 86 and drive down to a lower altitude, it is almost impossible that you are going to "hurt" the car. I think that most theories about low-octane gas causing damage are from the era before computerized engine control, and the concern is that you could cause predetonation (knocking). It is very hard to get a modern car to predetonate, particularly on an engine like the Volvo's (which has direct injection and variable valve timing, as well as variable spark advance). The car has a lot of ways to compensate, and it will as you descend into 'thicker' air, as measured by the car's mass air flow sensor. That is basically one of the major jobs of the ECU.
You may or may not get noticeably worse performance with the lower grade of gas, but that really depends on how aggressively you are driving, the altitude, etc. Some people will tell you it makes a huge difference, other people may not ever notice. Personally, I have never been able to tell the difference between 87 and 93 octane gas in my car (which has a 1.8L turbo-4 with about 11 psi of boost; your Volvo's engine has about 12-13) except when doing very aggressive autocross driving. So it has never seemed worth the price premium. YMMV, quite literally actually, so it's worth testing out and seeing how the car responds.
posted by Kadin2048 at 1:18 PM on November 3, 2014 [1 favorite]
Even if you were to fill up with 86 and drive down to a lower altitude, it is almost impossible that you are going to "hurt" the car. I think that most theories about low-octane gas causing damage are from the era before computerized engine control, and the concern is that you could cause predetonation (knocking). It is very hard to get a modern car to predetonate, particularly on an engine like the Volvo's (which has direct injection and variable valve timing, as well as variable spark advance). The car has a lot of ways to compensate, and it will as you descend into 'thicker' air, as measured by the car's mass air flow sensor. That is basically one of the major jobs of the ECU.
You may or may not get noticeably worse performance with the lower grade of gas, but that really depends on how aggressively you are driving, the altitude, etc. Some people will tell you it makes a huge difference, other people may not ever notice. Personally, I have never been able to tell the difference between 87 and 93 octane gas in my car (which has a 1.8L turbo-4 with about 11 psi of boost; your Volvo's engine has about 12-13) except when doing very aggressive autocross driving. So it has never seemed worth the price premium. YMMV, quite literally actually, so it's worth testing out and seeing how the car responds.
posted by Kadin2048 at 1:18 PM on November 3, 2014 [1 favorite]
I wondered the same thing too when I bought my BMW 328i wagon a couple of years ago. It's not a turbo, but it's a high-compression engine that is optimized for AKI89 (or AKI91? can't remember).
I read lots of arguments both for and against. At the end of the day, the argument that made the most sense to me was: if I can afford a BMW, I can afford premium fuel. The cost difference is trivial, and I'd rather not risk more expensive maintenance/repairs in the long term than usual because I skimped on the fuel.
posted by wutangclan at 1:30 PM on November 3, 2014
I read lots of arguments both for and against. At the end of the day, the argument that made the most sense to me was: if I can afford a BMW, I can afford premium fuel. The cost difference is trivial, and I'd rather not risk more expensive maintenance/repairs in the long term than usual because I skimped on the fuel.
posted by wutangclan at 1:30 PM on November 3, 2014
As a sidenote/bonus for those who find ECU nerdery interesting, here is an article on how automatic knock control works. (The article is specific to Hondas but virtually all modern engines work similarly, plus or minus some additional complexity based on the variables the engine has control over.)
In older cars, you had to do this by messing with the distributor if you heard the engine knocking; if you ignored it, that could cause damage — from thence comes all the cultural baggage about killing your car by using the wrong gas, I think.
Since the Volvo 2.0L engine is a "global powertrain" (used worldwide), it is almost certainly tested over a very wide range of fuel qualities. I'd be fairly comfortable betting that there is no gasoline sold in the US that would be completely out of bounds of the ECU's ability to compensate. (Lowest octane sold in the US is 85 R+M/2 octane and that's in Colorado, IIRC.)
posted by Kadin2048 at 1:31 PM on November 3, 2014
In older cars, you had to do this by messing with the distributor if you heard the engine knocking; if you ignored it, that could cause damage — from thence comes all the cultural baggage about killing your car by using the wrong gas, I think.
Since the Volvo 2.0L engine is a "global powertrain" (used worldwide), it is almost certainly tested over a very wide range of fuel qualities. I'd be fairly comfortable betting that there is no gasoline sold in the US that would be completely out of bounds of the ECU's ability to compensate. (Lowest octane sold in the US is 85 R+M/2 octane and that's in Colorado, IIRC.)
posted by Kadin2048 at 1:31 PM on November 3, 2014
Even if you were to fill up with 86 and drive down to a lower altitude, it is almost impossible that you are going to "hurt" the car.
Yea, but it'll work like crap.
A friend of mine has an older 5 cylinder v70. From what i've seen/heard from him, and what i've read online when i almost bought an 850 turbo, you not only get crappy performance but also lose enough in gas mileage that it's not even a savings.
What they mean by "regular gas wont damage anything" is just that, it's like how eating a gas station hotdog won't damage you. It doesn't mean it's what you actually should be eating.
Just buy premium the entire time. Whatever their equivalent of 92 is. You're just not saving that much getting the cheaper stuff, and you won't be getting the performance that's the point of getting a turbo car(barring tiny engines and turbodiesel stuff) nor the mileage it could get if driven conservatively.
posted by emptythought at 1:44 PM on November 3, 2014 [1 favorite]
Yea, but it'll work like crap.
A friend of mine has an older 5 cylinder v70. From what i've seen/heard from him, and what i've read online when i almost bought an 850 turbo, you not only get crappy performance but also lose enough in gas mileage that it's not even a savings.
What they mean by "regular gas wont damage anything" is just that, it's like how eating a gas station hotdog won't damage you. It doesn't mean it's what you actually should be eating.
Just buy premium the entire time. Whatever their equivalent of 92 is. You're just not saving that much getting the cheaper stuff, and you won't be getting the performance that's the point of getting a turbo car(barring tiny engines and turbodiesel stuff) nor the mileage it could get if driven conservatively.
posted by emptythought at 1:44 PM on November 3, 2014 [1 favorite]
I've lived in Colorado fro the last 6 years and have found that my vehicles run better/smoother and get better gas mileage with higher octane gas. I also notice an increase in power when driving into the mountains.
The cost is trivial between the low and the high octane, at most it might be a 4 dollar difference if I am filling up my whole tank.
posted by Divest_Abstraction at 2:21 PM on November 3, 2014
The cost is trivial between the low and the high octane, at most it might be a 4 dollar difference if I am filling up my whole tank.
posted by Divest_Abstraction at 2:21 PM on November 3, 2014
You might want to do the math on this one. Run a few tanks of regular and premium and hand calc your fuel economy. Make sure that the lowered fuel economy from your engine running on a lower performance map than it was optimized for doesn't cost more than the add'l cost of premium gas.
At the very least, never tell your dealer that you run 86, because they will try to use that fact to deny potential future warranty work.
posted by hwyengr at 5:01 PM on November 3, 2014
At the very least, never tell your dealer that you run 86, because they will try to use that fact to deny potential future warranty work.
posted by hwyengr at 5:01 PM on November 3, 2014
Kadin2048 is on the right track your car has essentially a Ford ecotec engine in it and running 85 through it will cause zero issues with that engine. The engine management controls fuel air mix so driving at high altitude is like driving with a dirty air filter - there will less oxygen available to burn so less fuel is put into the engine. You'll get roughly the same mileage high or low octane. The additional octane will change the engines timing to provide more power which why all of the power ratings for the engine are burning 93, to juke the stats favorably. However you'll find no authoritative source listing improved mileage and and folks like Consumers reports claiming no improvement. Try a couple tanks to see if the added cost is worth the added power- I suspect it won't be because the difference will be only few percent.
posted by zenon at 6:48 PM on November 3, 2014
posted by zenon at 6:48 PM on November 3, 2014
We have a new V60 and have only used 95 because that's what is recommended. Also, I think the engine is designed to use a specific octane level
posted by mattoxic at 2:31 AM on November 4, 2014
posted by mattoxic at 2:31 AM on November 4, 2014
Many European cars have the recommended octane inside the gas cap expressed in RON, which is a slightly different measurement from what is used on the pump in the US. 95 RON is equal to about ~90 AKI, which is what is marked on the pump in the US and Canada. (AKI is [RON+MON]/2, where RON and MON are two methods for measuring octane.)
I ran higher-than-necessary octane gas in my VW for a while before realizing that the "octane" they were recommending, when you read the fine print, was actually more like mid-grade at best. (And it didn't make a difference in casual driving anyway.)
It is not hard using a mileage-tracking app (or Fuelly) to keep tabs on your mileage and try a few different grades of gas. In my area, the price difference between different grades of gas is quite significant. There is no matching increase in mileage in my car. I do not dispute that in some cars, perhaps there is a difference in mileage, but I am very suspicious that anyone could say a priori that a particular engine is going to experience a decrease in fuel economy sufficient to justify the cost of higher-grade gas, without knowing a lot about the engine's internals and how it is going to compensate for octane.
At any rate, OP quotes directly from the Volvo manual in the question: "using 87 octane or above will not affect engine reliability." So the engine is clearly designed to accommodate 87 octane gas. It may be that the ECU is programmed for zero spark advance using 95RON/91AKI, but that's very different than an old carb'd engine which was really designed and tuned around a very particular octane and would run poorly on anything else.
posted by Kadin2048 at 12:08 PM on November 4, 2014
I ran higher-than-necessary octane gas in my VW for a while before realizing that the "octane" they were recommending, when you read the fine print, was actually more like mid-grade at best. (And it didn't make a difference in casual driving anyway.)
It is not hard using a mileage-tracking app (or Fuelly) to keep tabs on your mileage and try a few different grades of gas. In my area, the price difference between different grades of gas is quite significant. There is no matching increase in mileage in my car. I do not dispute that in some cars, perhaps there is a difference in mileage, but I am very suspicious that anyone could say a priori that a particular engine is going to experience a decrease in fuel economy sufficient to justify the cost of higher-grade gas, without knowing a lot about the engine's internals and how it is going to compensate for octane.
At any rate, OP quotes directly from the Volvo manual in the question: "using 87 octane or above will not affect engine reliability." So the engine is clearly designed to accommodate 87 octane gas. It may be that the ECU is programmed for zero spark advance using 95RON/91AKI, but that's very different than an old carb'd engine which was really designed and tuned around a very particular octane and would run poorly on anything else.
posted by Kadin2048 at 12:08 PM on November 4, 2014
I used to sell new Nissans for a living. They bring all the sales people out to these launch events when they introduce a new model or a major redesign and they usually have professional race car drivers that have driven Nissan factory cars somewhere and a couple of engineers. Nissans are another car where the manufacturer says, "Premium fuel recommended for highest performance." And somewhere else it says that regular is required. Lots of people were confused about it. At one of these launches, one of the Nissan guys there was a drive-train engineer so I asked him about it and he said to run them on regular.
If, at higher elevations, "regular" is 85 octane, use that.
I also remember reading a Car and Driver article where they got some cars that only required regular and some that required premium and then tested them on all three grades.
What they found was that all of them ran just fine on all fuels, cars that require regular don't gain anything by running on higher grades, and cars that require premium ran fine on regular but their mileage went down so far that it saved money to run them on premium. It was only a short term test though.
posted by VTX at 5:14 PM on November 4, 2014
If, at higher elevations, "regular" is 85 octane, use that.
I also remember reading a Car and Driver article where they got some cars that only required regular and some that required premium and then tested them on all three grades.
What they found was that all of them ran just fine on all fuels, cars that require regular don't gain anything by running on higher grades, and cars that require premium ran fine on regular but their mileage went down so far that it saved money to run them on premium. It was only a short term test though.
posted by VTX at 5:14 PM on November 4, 2014
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posted by mosk at 11:39 AM on November 3, 2014 [3 favorites]