That Annoying Engine Shut-off

AstroKats said:

Higher octane fuel won't make a difference. You'll get more power but only of the car is tuned for it.

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It's my experience that the vehicle is already "tuned for it." There is no where level where I live, no where. It's all either an up or a down while turning. Experiments with both octane and octane enhancing fuel mixes has provided me with optimum performance and optimum fuel mileages over the course of several newer vehicles.

I've also tuned and datalogged every mile of a variety of stock and extensively modified Subarus and am intimately familiar with real world, data backed, engine performance in this environment. I'm not guessing.

I also don't give a floating feather's energy to worry about pennies. I want the best on hand 100% of the time even if it's not used. So far I exceed estimates on all estimable parameters.

Others? Y'all, do youse.

Fate said:

It's my experience that the vehicle is already "tuned for it." There is no where level where I live, no where. It's all either an up or a down while turning. Experiments with both octane and octane enhancing fuel mixes has provided me with optimum performance and optimum fuel mileages over the course of several newer vehicles.

I've also tuned and datalogged every mile of a variety of stock and extensively modified Subarus and am intimately familiar with real world, data backed, engine performance in this environment. I'm not guessing.

I also don't give a floating feather's energy to worry about pennies. I want the best on hand 100% of the time even if it's not used. So far I exceed estimates on all estimable parameters.

Others? Y'all, do youse.

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Sounds like you have a really good handle on your use case ... and also like you have a very different use case from most of the folks on this forum. (For what it's worth, I do a lot of "up and down while turning" too, living in a mountaintop suburb about 1300 feet higher than Chattanooga, where I work and do most of my shopping and social activities.)

In the end, each of us has our own typical driving scenarios, and they may be quite different. It's interesting to hear from people all over the country and the world, but in the end, we all have to go with what works best in our own environment. I look forward to continued, spirited, and informing discussions.

Fate said:

It's my experience that the vehicle is already "tuned for it." There is no where level where I live, no where. It's all either an up or a down while turning. Experiments with both octane and octane enhancing fuel mixes has provided me with optimum performance and optimum fuel mileages over the course of several newer vehicles.

I've also tuned and datalogged every mile of a variety of stock and extensively modified Subarus and am intimately familiar with real world, data backed, engine performance in this environment. I'm not guessing.

I also don't give a floating feather's energy to worry about pennies. I want the best on hand 100% of the time even if it's not used. So far I exceed estimates on all estimable parameters.

Others? Y'all, do youse.

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Unless your car was knocking going up those hills you won't get a benefit from higher octane gas, it'll just cost you more.

It was my '19 Impreza's mini-motor that made me "worry about" the lowest margins of performance. It was a disappointment until I did a little of this and a little of that, then added octane to the mix. It struggled less. Then I discovered a passage in the OM concerning alternate, oxygen enriched, cleaner burning fuels... and added 5% methanol to my fill regimen.

That did it. The little motor that almost could didn't balk at the whip anymore, purred like a kitten, and became essentially flawless. The update to it's fuel maps that came later only gilded it's little lily.

That passage is in many OMs, BTW, including the '24's. Strange no one takes advantage of what is both a money saving as well as performance enhancing option... not to mention "more Green."

MountainJoe said:

Sounds like you have a really good handle on your use case ... and also like you have a very different use case from most of the folks on this forum. (For what it's worth, I do a lot of "up and down while turning" too, living in a mountaintop suburb about 1300 feet higher than Chattanooga, where I work and do most of my shopping and social activities.)

In the end, each of us has our own typical driving scenarios, and they may be quite different. It's interesting to hear from people all over the country and the world, but in the end, we all have to go with what works best in our own environment. I look forward to continued, spirited, and informing discussions.

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Beautiful area. My parents just moved out in that area, and I'm in Dallas Georgia.

AstroKats said:

Unless your car was knocking going up those hills you won't get a benefit from higher octane gas, it'll just cost you more.

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I have yet to hear a Subaru knock. Their ECUs are far more sophisticated than that, further enhanced by our later motors' addition of another knock sensor to augment the previous models' only one. The ECU anticipates knock before it occurs, and seamlessly reduces torque to the level below the calculated knock threshold. IOW, waiting to actually hear KNOCK is way too late to address it.

Of course, without a background in correlating data with the empirical one is left to rely on theory.

As for "costing more," that's a "compared to what" situation, IMHO. That's no one's business but mine.

Fate said:

I have yet to hear a Subaru knock. Their ECUs are far more sophisticated than that, further enhanced by our later motors' addition of another knock sensor to augment the previous models' only one. The ECU anticipates knock before it occurs, and seamlessly reduces torque to the level below the calculated knock threshold. IOW, waiting to actually hear KNOCK is way too late to address it.

Of course, without a background in correlating data with the empirical one is left to rely on theory.

As for "costing more," that's a "compared to what" situation, IMHO. That's no one's business but mine.

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As you like to say, you do you. I'm commenting for others who might come here looking for help. Here's a AAA article about it:

AstroKats said:

As you like to say, you do you. I'm commenting for others who might come here looking for help. Here's a AAA article about it:

Don't Confuse Gasoline Octane And Quality

Is there a difference between regular and premium gasoline? If you don't use the gasoline required or recommended by the manufacturer, could it cause problems? To understand the answers to these questions and to save yourself thousand in auto repair bills you need to understand the differences...

www.aaa.com

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That is the exact same reason for my posts as well... to help others looking for information, not to argue nor contradict, but to offer my PERSONAL experiences. If I differ from the blurbs of AAA, Powers, or any other middle of the road, lifeless, data crunchers then, well, that justifies my posts as a consideration for those readers whose situations may also not fit the size 6 speculations of the paid mouths. Those are everywhere one looks. This is a FORUM after all, not a bibliography of statistically relevant scholarly papers.

If you want more information about the background from which I come, PM me. I've said enough here.

Fate said:

That is the exact same reason for my posts as well... to help others looking for information, not to argue nor contradict, but to offer my PERSONAL experiences. If I differ from the blurbs of AAA, Powers, or any other middle of the road, lifeless, data crunchers then, well, that justifies my posts as a consideration for those readers whose situations may also not fit the size 6 speculations of the paid mouths. Those are everywhere one looks. This is a FORUM after all, not a bibliography of statistically relevant scholarly papers.

If you want more information about the background from which I come, PM me. I've said enough here.

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I'd prefer you post some links to back up your theories, from respectable organizations. Otherwise, they are just that, your own theories. And not about race cars, about ordinary consumer vehicles recommended to use 87 octane.

Here's another one by Consumer Reports:


I use Premium in my Lotus but it has a twin turbo V8 and is essentially a street legal race car.

Or you can be like me and live at 7,000 feet and LOWER octane is just fine! Mostly stations here sell 86 and I've never had an issue. (I read that Denver, situated at a lowly 5,000 feet sells 85 octane as regular.)

Concerning AS/S (2024 Crosstrek) I sort of like it. Kind of disconcerting the first few times it kicked in! But, it's super easy to keep it from coming on just by using light pressure on the brake pedal when at a stop light or whatever. What I do find somewhat bothersome is it seems to be somewhat random in operation, generally in when it comes on. If the A/C is on it usually won't engage, other times it doesn't come on when I want. Rarely does it engage when I don't want it.

charliefreeman said:

Or you can be like me and live at 7,000 feet and LOWER octane is just fine! Mostly stations here sell 86 and I've never had an issue. (I read that Denver, situated at a lowly 5,000 feet sells 85 octane as regular.)

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That makes sense, the air is less dense, so less oxygen. Do you guys up there get a special tune? I've found the Crosstrek to be very sluggish over 7K in the Sierras, especially in the summer when the air is warmer so even less dense.

I have no idea if we tune cars differently. My 2024, purchased 3 weeks ago, came off the truck and into my hands with exactly 1 mile on the odometer, so it's unlikely the factory tuned it differently just because it was coming to New Mexico. And, we never get below 5,000 feet, so I can't compare performance between altitude and the flats. Having lived here for almost 26 years and having owned a number of different makes and models, include now 4 Subarus, every single mechanic, dealer or independent have said regular, lower octane is just fine. The only exception was with cars designed for premium the recommendation was almost always stick with the highest octane.

MountainJoe said:

Right. Unless you are experiencing engine knock with regular fuel, paying extra for the "good stuff" isn't really accomplishing anything except emptying your wallet faster.

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If you are experiencing engine knock in these cars, you have a problem that needs to be repaired. Solving it with premium gas is a Band-aid on a broken leg.

MA Subie said:

If you are experiencing engine knock in these cars, you have a problem that needs to be repaired. Solving it with premium gas is a Band-aid on a broken leg.

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I speak only from experience with driving older cars (my current Trek is the first car I ever bought brand new). I had a couple in the past (1983 Corolla, 2000 Forester) that ran OK on regular fuel when I first got them, but eventually (I suppose due to engine wear/loss of compression) got to the point where I had to run premium in them to avoid knocking and other performance issues. Maybe it was "a Band-Aid on a broken leg," but it got me by when I couldn't afford a newer car or rebuilding an engine.

On the other hand, I never had to run premium in the 2004 Forester I was driving until March of this year; it ran just fine on regular (although I had to replace the knock sensor awhile back ... it knocked like crazy when the original one went out). Long story short, it seems to be needed (or at least help) on some older cars, but not others.

charliefreeman said:

The only exception was with cars designed for premium the recommendation was almost always stick with the highest octane.

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People confuse octane rating with power, even purported experts. The octane rating is the ability of the fuel to remain stable under compression. If a car is designed for 87 then, due to its compression ratio, 87 will be fine and there will be no advantages to using a higher octane fuel, it will just cost you more. Performance vehicles, especially turbos like my Lotus, have higher compression ratios so benefit from premium fuel. The performance increase comes from the higher compression ratio, not the fuel itself.

As @MA Subie wrote, if you're experiencing knocking with the recommended fuel then you may have other issues and if not fixed it could cause serious engine damage over time.

MountainJoe said:

Not gonna happen. My money, I spent it on my car, I want it to operate the way I expect. And I don't want that kind of wear and tear on my battery and starter, just to save some infinitesimal amount of fuel.



Well, that's a battle for the next generation to fight. I'm old enough to complain about "features" like this and also to (unfortunately have to) pay for a workaround. There will always be workarounds (legal or not) for anything that annoys enough people. All you have to do is look at the plethora of fake vax cards circulating during COVID to see what people will do when you try to force something on them that they emphatically do not want.

Time to go cue up "Red Barchetta" by Rush....

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Auto Start/Stop saves between 4% and as much as 15% of fuel used in city driving. Even at 4%, that's not infinitesimal. However, the additional use of the battery, starter and other systems is minimal and more than offset by fuel savings.

Blue Bendite said:

Auto Start/Stop saves between 4% and as much as 15% of fuel used in city driving. Even at 4%, that's not infinitesimal. However, the additional use of the battery, starter and other systems is minimal and more than offset by fuel savings.

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Not sure if anyone has done long term testing on this. For me, it would be the annoyance of the car shutting down every time I stopped. I had it on a rental car in England and hated it. Lots of roundabouts there and it was a nightmare trying to merge into the flowing traffic when the engine had just died.

There is a lot of work put into these 'start/stop' systems. When I was working with JLR projects, we were surprised to find that the engine valve train is activated hydraulically so that the valves can be open when the engine is started to lessen the load for cranking... I don't know if Subaru have a similar device to minimise impact on the the starter and battery?
We also worked investigating battery drain problems with a vehicle that was start/stop and customers were finding that their batteries were failing early. The battery manufacturers who were being blamed for a shoddy product insisted that the auto manufacturers were cheaping out on the OEM batteries that they were providing for installation in new vehicles to save a few pennies... So tricky to know - but it does seem that A/S/S cars do need an uprated battery.

Graphite said:

There is a lot of work put into these 'start/stop' systems. When I was working with JLR projects, we were surprised to find that the engine valve train is activated hydraulically so that the valves can be open when the engine is started to lessen the load for cranking... I don't know if Subaru have a similar device to minimise impact on the the starter and battery?
We also worked investigating battery drain problems with a vehicle that was start/stop and customers were finding that their batteries were failing early. The battery manufacturers who were being blamed for a shoddy product insisted that the auto manufacturers were cheaping out on the OEM batteries that they were providing for installation in new vehicles to save a few pennies... So tricky to know - but it does seem that A/S/S cars do need an uprated battery.

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Lots of battery threads here. Our OEM battery died after a year and that's without AS/S. After some research, including here, I replaced it with an Odyssey Extreme AGM. Probably overkill but didn't have a problem after that.

It's not just saving pennies, it's saving a few ounces here and there to meet CAFE standards.

Blue Bendite said:

Auto Start/Stop saves between 4% and as much as 15% of fuel used in city driving. Even at 4%, that's not infinitesimal. However, the additional use of the battery, starter and other systems is minimal and more than offset by fuel savings.

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I'd like to see some citations on that, because in my experience based on where I drive, there is absolutely no way that a/s/s would save anything close to 4%, let alone 15%. For a car that averages 30 MPG overall, 4% would be 1.2 MPG and 15% would be a ludicrous 4.5 MPG ... not gonna happen ... not unless you are in someplace like NYC and literally stopping for a red light every block at rush hour or something, and probably not even then.

Conversely, we have had plenty of reports right here on this forum of people having to replace batteries prematurely on cars with this "feature." I don't know about starters ... that would seem to be a longer-term problem ... but one I'm not willing to chance. I'll gladly pay the $27 for the eliminator cable and a few pennies more for fuel each fill-up to avoid those headaches (and expenses).