87 or 91+ octane?

[jaymz]

Run what you want. The difference in cost is only gonna be $2-3 per tank, which likely isn’t going to send anyone to the poorhouse.

 

[WRANBO]

I am using 87 Octane and am getting good performance and mileage, 7.4L/100km, currently at 41,000km

 

[Grayrat]

Run what you want. The difference in cost is only gonna be $2-3 per tank, which likely isn’t going to send anyone to the poorhouse.

I ran 91 octane for the first couple thousand miles. My dealer service guy told me that I was wasting my money, so I switched to 87 and it has no effect on gas mileage or performance on my particular Jeep. Also, where I live in Nevada, and even more so out on the open road, going to the mountain or desert areas, 91 is typically 50 cents a gallon more, which I typically fill up with about 17 gallons, so do the math and decide whatever you want to do. I disagree with your numbers, but I do agree that based on how much more everything costs (food, labor for service and repairs, etc.) an extra $8 a week is the cost of a meal for one at a fast food drive thru, with a discount coupon.. LOL.

 

[Zandcwhite]

I ran 91 octane for the first couple thousand miles. My dealer service guy told me that I was wasting my money, so I switched to 87 and it has no effect on gas mileage or performance on my particular Jeep. Also, where I live in Nevada, and even more so out on the open road, going to the mountain or desert areas, 91 is typically 50 cents a gallon more, which I typically fill up with about 17 gallons, so do the math and decide whatever you want to do. I disagree with your numbers, but I do agree that based on how much more everything costs (food, labor for service and repairs, etc.) an extra $8 a week is the cost of a meal for one at a fast food drive thru, with a discount coupon.. LOL.

My dealer service rep argued with me for 20 minutes that our 2019 2.0t with etorque still had the auxiliary 12v battery under the fuse panel, I would put 0 faith in anything they tell you. The manual clearly states that you should run higher octane fuel for optimal performance. It's not debatable. It's 100% fact from the manufacturer. It also states that the jeep will run fine on 87. Run what you want, but it absolutely does have an effect on performance. We are likely talking 5-15hp tops, you'll likely not notice it but it is there regardless. People spend $400-800 on cold air intakes for about the same gain.

 

[Grayrat]

My dealer service rep argued with me for 20 minutes that our 2019 2.0t with etorque still had the auxiliary 12v battery under the fuse panel, I would put 0 faith in anything they tell you. The manual clearly states that you should run higher octane fuel for optimal performance. It's not debatable. It's 100% fact from the manufacturer. It also states that the jeep will run fine on 87. Run what you want, but it absolutely does have an effect on performance. We are likely talking 5-15hp tops, you'll likely not notice it but it is there regardless. People spend $400-800 on cold air intakes for about the same gain.

I get what you are saying.....but truthfully, and I am a total performance fanatic, but my Jeep is plenty fast enough on the street. Considering all of my modifications have been directed toward offroad performance and durability. BTW, the Mishimoto high performance air intake which I have, and is really not a "cold air intake" was never intended to be used as you would on a hot rod. It is there to provide increased airflow in the dirt, with a larger filter housing and a fabric material (dry is my preference because the dust sticks too much to the oiled filters in my neck of the woods). And I feel it is essential to replace the stock paper filter which is already restrictive, with something that turns to junk quickly when driving with a bunch of off roaders out in the desert or up in the hills. Every vehicle I own gets the stock paper filter element replaced within the first month of purchase. So just as a word of advice, don't buy a filter system for your off-road Jeep, that has a big fully exposed, oiled element. I have a K&N oiled type on my street only Mustang GT which is located to pull in fresh air instead of hot air under the hood from the front, and it has to be scrubbed every few months, blown out the bugs and re-oiled with the car never touching a dirt road. That filter has lasted the last 5 years, and it is still serviceable. I would never consider one for a Jeep, unless you wanted to convert it into a street rod, or a mall crawler. In that case, go for it.

 

[jjvincent]

@stumblinhorse,

Keep being curious, there should never be a 'last' question. That's how science works (really). Question everything all the time. At some point as your knowledge grows, this curiosity becomes more than just that. You develop an interest or a passion and deeper understanding then only expands exponentially. The human brain is a remarkable thing. Always seek answers to whatever questions you can dream up.

I always say that education isn't formal it's inherent. College very rarely teaches you many answers, but it does teach you where to go look them up. You don't need specialized degrees to truly understand.

As for your continued curiosity in all things engine related, this answer is tricky because there are several approaches based on what you have to work with. Not all engine controllers are created equally. It generally depends on the 'horsepower' of the CPU and it's available memory and overall hardware architecture.

Since sophistication requires cost, the cheaper the vehicle, typically the more simple the controller. In fact in many low-end automobiles, the engine, transmission and body management are all performed in a single Powertrain Control Module (PCM). In more higher-end products the control is more distributed and each component has it's own dedicated computer. Each implementation has it's particular pros and cons. Such as simple information coordination vs complicated communication signalling, typically over several Controller Area Network (CAN) buses throughout the entire vehicle.

Given a powerful enough processing platform where lots of control logic is built into the controller along with high bandwidth CPU's, the spark timing equations are many orders of magnitude more sophisticated. The lower bandwidth engine control schemes offer a wholly different spark timing approach.

Since our JL's have a really decent engine control solution, I'll just briefly explain the more fundamental, (simpler) approach first.

On controllers with only the most marginal amount of information available, spark timing is more 'reactionary' rather than 'predictive'. In this scenario, spark is incrementally advanced until 'badness' starts to happen such as lower performance, more emissions or even knock. At which point the controller reverses this advance and begins to then retard it. It does this until once again 'badness' begins to happen yet again. This time, it will be almost totally dependent on performance and emission monitors since pre-detonation is more unlikely.

This ping-pong of 'too advanced' or 'too retarded' is always going on to some degree. The computer software algorithms are generally designed to learn a sweet spot' where the engine is running optimally. However, there are of course many factors that will alter this sweet spot. Things like engine load, stochiometric fuel/air dynamics, emissions, fuel quality, octane value and others. So the spark equation is continually hunting for and ever changing this sweet spot. Of course there are maximum and minimum spark timing thresholds which are constrained to certain absolute piston positions in relation to Top-Dead-Center (TDC) in order to prevent engine damage. But, this solution typically ping pongs back and forth as engine dynamics change, which they do all the time.

Now moving on to the more sophisticated approach. This invests in more of a predictive model. This requires a lot more monitoring of just about anything the auto company is willing to invest in. Typically more pressure, emissions and knock sensors or at least a way to derive them through statical analysis performed in real time.

Within this environment, the Calibration Team (the true engine scientists) perform all the math and physics modeling to monitor, track and predict what the most optimal spark timing needs to be. Rather than the trial and error (ping pong) approach, spark timing is always advanced just enough to provide the most optimum combustion, but no more. This timing should (in theory) prevent or minimize knock. However, we know from a previous post, that with low octane, the probability increases to where the fuel/air mix may pre-detonate on it's own before the optimal ignition point within the piston's cycle, outside of software control.

If knock happens, as within the more simple algorithm, the spark timing will be retarded along with more aggressive fuel/air mixture adjustments.

The benefit of this sophistication however is to greatly minimize knock and undesired emissions generation while improving performance. Modern Engine Controllers excel at this. Essentially because the ever increasing CAFE and emmision regulatory mandates provide the auto companies with essentially no other options.

So the Calibrators are hired and tasked with solving all the very complicated calculus and statistical math in real time. They do this though the use of various data structures defining one dimensional vectors, two dimensional surfaces, three dimensional maps and higher dimensional abstractions. The differential and matrix algebra equations are necessary to solve the physics of predicting not only the fuel/air mix but the most optimal piston position in order to deliver the most beneficial ignition point with the never ending goal of producing Stochiometry.

Without this sophistication, all ICE vehicles would immediately fail the latest emission regulations. The lower-end products would still have to pay the 'carbon' fines, but the car companies get somewhat of a pass as long as their fleet averages satisfy EPA thresholds. So over time even more sophistication will be required until every vehicle running on dinosaur goo is phased out.

Unfortunately (IMHO), the battery tech that is being offered is still not a practical viable alternative. We need something better, not worse before we eliminate our current 'horse' power.

I know I really touched on a lot of things here. I really hope it helps you towards a better understanding.

Stay inquisitive.
Jay

What's interesting is one of the crew members that I work with in racing has a day job working as an engineer at a large company that designs and tests OEM engines. So he has up to date knowledge of that is going on when it comes to testing (he works in the test lab). We literally had this conversation about octane and engines.

According to him, manufacturers know people will not use the best of the best. Thus they have to calibrate the engine for a wide range of conditions and that includes fuel. Plus, the general public cannot actually determine what is going in their tank, thus they can get a sub par tank of fuel but last thing a manufacturer needs are engines detonating themselves to death. As you know today, we can get that warning on the dash and the engine can go into limp mode when needed.

With that, being a forced induction engine actually give them an extra part of their kit to adjust and keep detonation from happening. Then we have advancements in processing power vs cost. Top it off, the testing (as you have seen) it over the top as compared to what the general public does. Most manufacturers will run as low as 82 octane for calibrations. I would consider the motor in the Jeep as a run of the mill engine. Nothing special.

In the real world, these engine will be mistreated and in the end, outlast the rest of the vehicle. End up in a salvage yard where it just becomes the increasing pile of mass where very few get bought (unless there's a race application for it then people buy them up). If people would just treat the rest of their vehicle like they do with things like motor oil and gas, maybe they will be able to wear out that big hunk in the front. As a fellow engineer, you look at numbers. When you look at the number of failures of powerplants vs the rest of the vehicle, the powerplants now win. 40 years ago, not the case. Times have turned.

We need to keep up to date.

John

 

[Zus]

Where I live at altitude, octanes available are 85, 87 and 91, so if Jeep says 87 is ok at lower elevations where octanes available are 87, 91, and 93, am I correct to assume 85 would work fine at higher altitudes?

 

[tk1700]

Where I live at altitude, octanes available are 85, 87 and 91, so if Jeep says 87 is ok at lower elevations where octanes available are 87, 91, and 93, am I correct to assume 85 would work fine at higher altitudes?

I live at 7000ft and most of my driving is between 5000 and 9000 ft. I use 85/86 in a 2019 3.6 and 2021 2.0. I haven't had any problems and average 20-24 mpg.

 

[Shibadog]

The thread that never dies. READ the manual, put on your grown up clothes and buy what YOU want. The “gotta have 91“ folks will never convince the “87 only” folks. The engineers who developed the darn thing should know more about it than the armchair quarterbacks. READ what they say in the manual and decide what works for you-know need to try and justify your decision either way…

 

[JP29]

The thread that never dies.…

Someone literally asked a new question yesterday, so if you're tired of it, move along.

 

[Pinky Tuscadero]

Run what you want. The difference in cost is only gonna be $2-3 per tank, which likely isn’t going to send anyone to the poorhouse.

$2-3 per tank I'd get it every time for sure
Here in SE Wisconsin it's 80-90 cents more per gallon so
even at 80 cents x 21 gallon tank = $16.80 per tank
I suppose it depends on your location then for the extra cost so I can see why this wouldn't be an issue for some then - thanks

 

[JP29]

$2-3 per tank I'd get it every time for sure
Here in SE Wisconsin it's 80-90 cents more per gallon so
even at 80 cents x 21 gallon tank = $16.80 per tank
I suppose it depends on your location then for the extra cost so I can see why this wouldn't be an issue for some then - thanks

Also have to factor in two door versus four door, or 17 versus 21 gallons at empty

 

[Grayrat]

The main reason this is becoming such a sensitive issue, is that ALL GAS has gone up so dramatically, that "we" as enthusiasts have to decide whether it is worth getting into the car to get something at the store, running an errand, or should I wait until I have 3 or 4 places I need to go and save them up for a single trip out of the driveway. My fillups are now $100 per tank in my county. Makes me have to decide whether I need to go to the store, go out to eat, or whether a weekend playing out in the dirt is going to effect the rest of my lifestyle. Should I go out with my girl for a nice dinner out, and maybe drinks or a show, or do I go Jeeping? Should I give up on buying a couple steaks, so I can keep my weekly budget closer to what it was a year ago? And for anyone who is reading this thinking "I should have waited for the electric version"? I saw on the news last night that this summer is going to potentially have a lot of brown outs, with no electricity, so how is that going to effect those who chose that route. I think we should be thankful that our Jeeps can run on 87. As 87 seems to be the least affected price of all the grades, and diesel is absolutely insane. I just drove by a few stations, they were within a few cents of each other. Best price on 87 was $4.87/gallon and diesel was $5.59/gallon. These were the cheaper stations. The Chevron and Shell stations were all over $5.00/gallon for 87, and these advertised prices most with a caveat: some were cash only and some were with car wash. When I was paying $3/gallon, an extra 20 cents for premium was no big deal. My Jeep is my daily driver and I put 1000 miles a month on it, without including vacation trips. So at 15 mpg average, which does not include my offroad mileage which is less because I'm playing in the loose and slippery dirt, sandwashes, hill climbs, rock quarries, which don't register a lot of miles but are burning up a tank of gas in a 30 mile area, I am only spending an extra $33/month for premium, but if you look at what I was paying a year ago, I am now spending $132/ a month not including the $33 premium upgrade. Factor in the price of food, which seems to have gone up 50% in the real world, and compromises have to be made. All my other vehicles 4 m/c's, RZR Turbo, Mustang GT all say 91 octane minimum, and they all have performance upgrades that make it essential, no cheating. My Jeep doesn't have tuner or a remapped ECU or a cat-less full exhaust, or cams, etc. like the m/c''s do, but it merely has an intake (which is basically for better dirt protection over the stock paper element, a Borla cat back exhaust which just improves ground clearance and makes more sound, and a intercooler tube, which is cast aluminum replacing the stock plastic one, which makes it a little more efficient, but seriously, with the heat and pressure generated by the small turbo engine, it was a cheap and easy upgrade, compared to replacing a turbo prematurely. (I had a Volve back 20 years ago that blew a Turbo at 60K and it was $3500 to replace back then. Now it is probably double that. For the first time in a long time, I'm looking at the overall big picture of how much it costs to use, maintain, and upgrade my vehicles of the life of the vehicle. I put money into skid plates, because I don't want to even think about the cost of what a rock can do to the coolant lines for the trans, oil pan, differentials/ axle housings. Check with your local dealer and ask what the availability of those parts are currently from Jeep. They suck. Plan on 2,3,4 months, heck upgrading your axles from the 2 main manufacturers are a year or more backordered. I know I am going off in a different direction, but as a fellow member of the 2.0Turbo family, take a look under your Jeep and ask yourself what parts look vulnerable that could cause major parts failures under your car. I was shocked. Fortunately, M.O.R.E. in Colorado has a full set of skids that clean up all those spots that are not too expensive, and are easy to service, especially around the oil pan and trans. They even have an opening tor changing the oild without removing anything. And you can get the owner of the company on the phone if you have questions or installation issues.

 

[Zus]

I live at 7000ft and most of my driving is between 5000 and 9000 ft. I use 85/86 in a 2019 3.6 and 2021 2.0. I haven't had any problems and average 20-24 mpg.

Thanks TK, I appreciate it.

 

[Paulcardona]

@stumblinhorse,

Keep being curious, there should never be a 'last' question. That's how science works (really). Question everything all the time. At some point as your knowledge grows, this curiosity becomes more than just that. You develop an interest or a passion and deeper understanding then only expands exponentially. The human brain is a remarkable thing. Always seek answers to whatever questions you can dream up.

I always say that education isn't formal it's inherent. College very rarely teaches you many answers, but it does teach you where to go look them up. You don't need specialized degrees to truly understand.

As for your continued curiosity in all things engine related, this answer is tricky because there are several approaches based on what you have to work with. Not all engine controllers are created equally. It generally depends on the 'horsepower' of the CPU and it's available memory and overall hardware architecture.

Since sophistication requires cost, the cheaper the vehicle, typically the more simple the controller. In fact in many low-end automobiles, the engine, transmission and body management are all performed in a single Powertrain Control Module (PCM). In more higher-end products the control is more distributed and each component has it's own dedicated computer. Each implementation has it's particular pros and cons. Such as simple information coordination vs complicated communication signalling, typically over several Controller Area Network (CAN) buses throughout the entire vehicle.

Given a powerful enough processing platform where lots of control logic is built into the controller along with high bandwidth CPU's, the spark timing equations are many orders of magnitude more sophisticated. The lower bandwidth engine control schemes offer a wholly different spark timing approach.

Since our JL's have a really decent engine control solution, I'll just briefly explain the more fundamental, (simpler) approach first.

On controllers with only the most marginal amount of information available, spark timing is more 'reactionary' rather than 'predictive'. In this scenario, spark is incrementally advanced until 'badness' starts to happen such as lower performance, more emissions or even knock. At which point the controller reverses this advance and begins to then retard it. It does this until once again 'badness' begins to happen yet again. This time, it will be almost totally dependent on performance and emission monitors since pre-detonation is more unlikely.

This ping-pong of 'too advanced' or 'too retarded' is always going on to some degree. The computer software algorithms are generally designed to learn a sweet spot' where the engine is running optimally. However, there are of course many factors that will alter this sweet spot. Things like engine load, stochiometric fuel/air dynamics, emissions, fuel quality, octane value and others. So the spark equation is continually hunting for and ever changing this sweet spot. Of course there are maximum and minimum spark timing thresholds which are constrained to certain absolute piston positions in relation to Top-Dead-Center (TDC) in order to prevent engine damage. But, this solution typically ping pongs back and forth as engine dynamics change, which they do all the time.

Now moving on to the more sophisticated approach. This invests in more of a predictive model. This requires a lot more monitoring of just about anything the auto company is willing to invest in. Typically more pressure, emissions and knock sensors or at least a way to derive them through statical analysis performed in real time.

Within this environment, the Calibration Team (the true engine scientists) perform all the math and physics modeling to monitor, track and predict what the most optimal spark timing needs to be. Rather than the trial and error (ping pong) approach, spark timing is always advanced just enough to provide the most optimum combustion, but no more. This timing should (in theory) prevent or minimize knock. However, we know from a previous post, that with low octane, the probability increases to where the fuel/air mix may pre-detonate on it's own before the optimal ignition point within the piston's cycle, outside of software control.

If knock happens, as within the more simple algorithm, the spark timing will be retarded along with more aggressive fuel/air mixture adjustments.

The benefit of this sophistication however is to greatly minimize knock and undesired emissions generation while improving performance. Modern Engine Controllers excel at this. Essentially because the ever increasing CAFE and emmision regulatory mandates provide the auto companies with essentially no other options.

So the Calibrators are hired and tasked with solving all the very complicated calculus and statistical math in real time. They do this though the use of various data structures defining one dimensional vectors, two dimensional surfaces, three dimensional maps and higher dimensional abstractions. The differential and matrix algebra equations are necessary to solve the physics of predicting not only the fuel/air mix but the most optimal piston position in order to deliver the most beneficial ignition point with the never ending goal of producing Stochiometry.

Without this sophistication, all ICE vehicles would immediately fail the latest emission regulations. The lower-end products would still have to pay the 'carbon' fines, but the car companies get somewhat of a pass as long as their fleet averages satisfy EPA thresholds. So over time even more sophistication will be required until every vehicle running on dinosaur goo is phased out.

Unfortunately (IMHO), the battery tech that is being offered is still not a practical viable alternative. We need something better, not worse before we eliminate our current 'horse' power.

I know I really touched on a lot of things here. I really hope it helps you towards a better understanding.

Stay inquisitive.
Jay

Thanks for all your explanations.

Does that mean that in my 3.6 sometimes getting better octane fuel it will be better? even for "cleaning" purposes? I can get here even 98 octane fuel.


Thanks a lot

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