3.6 engine and 87 octane a no-no

[Pape]

Alas- soon we will have to resurrect oil threads, I haven’t seen one in days, heck weeks— Whose Gonna Fill His Shoes ? Now, what about this controller Thingy ?

are you experiencing the Stockholm syndrome or what, lol :P

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[DanW]

Here is what Kevin, a former Jeep powertrain engineer who was on the gen 1 Pentastar design team, told me about running higher octane than 87 in the Pentastar. You can search him on BITOG as Oil_Udder and see if you can find some similar discussions.

He said first of all, there is zero power benefit. Not 1 additional horsepower will come from running 93 octane compared to 87. Some 93 octane gas, like Shell V-Power, has additional additives to clean fuel injectors, valves, etc, but the octane itself does nothing in that arena. Many brands of gas have the same exact additive detergent package as their 87 gas.

But there is one advantage of which he told me. I will do my best to describe it, but I will try to find the conversation (I believe it was via PM on BITOG, but I am not sure). Anyway, he said the way the higher octane gas explodes is very VERY slightly gentler on the engine....in other words, it ¨softens¨ the mechanical impact of the combustion process on the pistons, rods, and crank shaft. It is so slight that he said only the multimillion dollar testing equipment used in the development and testing of the engine can detect it. But it is definitely there.

So, when someone says their engine runs smoother on higher octane gas, it is actually true. The part that is debatable is whether they can detect it. From our conversation, I´d conclude that Kevin would believe a human being would not be able to sense the difference.

In my JL and JT Pentastars, I run 87 almost exclusively. Mainly Top Tier gasoline brands. I will on rare occasion run a tank of Shell V-Power through them instead of paying for a fuel system cleaner. I´ve had no knocking or pinging, even when under a hard load at any rpm, including towing up steep hills in hot weather.

As others have said. If it makes you feel better or you sense the engine is smoother running higher octane, by all means do it. Is it a waste of money? Hell, I´ve had people tell me driving a thirsty Jeep is a waste of money. And I don´t care. I enjoy it, so that´s all that matters to me.

 

[Bob Burd]

I run cheapest gas I can find, and change the oil when my Jeep tells me to. 220Kmi so far.
But I do run an RPM fan controller and change the auto trans fluid every 60Kmi or so.

 

[Kracka]

Does Amsoil make gas?

Asking for a friend.

 

[Wabujitsu]

What tires are the best? And what pressure should I run?

It depends on what weight of oil and octane of fuel you are running. For instance, the lower the octane, the higher your tire pressure should be - unless you use 10W40 or above. In that case, you divide by the number of tires and multiply by the number of accessories installed on your Jeep.

 

[desmo2]

It depends on what weight of oil and octane of fuel you are running. For instance, the lower the octane, the higher your tire pressure should be - unless you use 10W40 or above. In that case, you divide by the number of tires and multiply by the number of accessories installed on your Jeep.

OK, but does each individual duck on my dash count as a separate accessory? They are all precious to me so I think they should, but I don't know if the science agrees?

 

[Wabujitsu]

OK, but does each individual duck on my dash count as a separate accessory? They are all precious to me so I think they should, but I don't know if the science agrees?

Dave, it depends on whether the ducks are attached to your dashboard, e.g. Velcro, or not. Any aftermarket thingie (now I’m channeling @Jeep_Junkie) is counted as an accessory, even if it serves no useful purpose, if it is attached.

 

[Fatbob Frank]

We run 87 (no Eth) exclusively cause 91 is nearly $.80 more per gallon and thus reserved for my motorcycles or General..
It gets 2mpgs better on average on regular than the cheaper 10-15% Ethanol stuff.
And the dreaded "low speed hesitation" is almost non existent too...

 

[WranglerMan]

I have ran the cheap 87 for years in my 2018 and no issues that I’m aware of.

 

[Fish]

I run Diesel in my 3.6 it loves it, no pings or doorbells.

 

[ASSFROW]

It depends on what weight of oil and octane of fuel you are running. For instance, the lower the octane, the higher your tire pressure should be - unless you use 10W40 or above. In that case, you divide by the number of tires and multiply by the number of accessories installed on your Jeep.

Ok, so using that formula I came up 1344. I hit a speed bump this morning in the mall parking lot and now I'm in orbit. The positive part of my journey is with the weather in Maryland rn it's warmer in space.

 

[alphawolff]

Here is what Kevin, a former Jeep powertrain engineer who was on the gen 1 Pentastar design team, told me about running higher octane than 87 in the Pentastar. You can search him on BITOG as Oil_Udder and see if you can find some similar discussions.

He said first of all, there is zero power benefit. Not 1 additional horsepower will come from running 93 octane compared to 87. Some 93 octane gas, like Shell V-Power, has additional additives to clean fuel injectors, valves, etc, but the octane itself does nothing in that arena. Many brands of gas have the same exact additive detergent package as their 87 gas.

But there is one advantage of which he told me. I will do my best to describe it, but I will try to find the conversation (I believe it was via PM on BITOG, but I am not sure). Anyway, he said the way the higher octane gas explodes is very VERY slightly gentler on the engine....in other words, it ¨softens¨ the mechanical impact of the combustion process on the pistons, rods, and crank shaft. It is so slight that he said only the multimillion dollar testing equipment used in the development and testing of the engine can detect it. But it is definitely there.

So, when someone says their engine runs smoother on higher octane gas, it is actually true. The part that is debatable is whether they can detect it. From our conversation, I´d conclude that Kevin would believe a human being would not be able to sense the difference.

In my JL and JT Pentastars, I run 87 almost exclusively. Mainly Top Tier gasoline brands. I will on rare occasion run a tank of Shell V-Power through them instead of paying for a fuel system cleaner. I´ve had no knocking or pinging, even when under a hard load at any rpm, including towing up steep hills in hot weather.

As others have said. If it makes you feel better or you sense the engine is smoother running higher octane, by all means do it. Is it a waste of money? Hell, I´ve had people tell me driving a thirsty Jeep is a waste of money. And I don´t care. I enjoy it, so that´s all that matters to me.

The gen 1 is completely different than the gen 2.

Gen 2 increased compression and made that octane level an important factor. On the gen 1 it made very, very little difference. On the gen 2 you can feel an immediate difference with the higher octane under certain load conditions. On my 2020 JT it was a massive difference changing to just 89 octane. I personally recommend 89 for PUG 3.6Ls.

The reason it runs "smoother" is because the combustion cycle is properly completing at its targeted engine timing. If the engine begins to sense knock due to the lower octane, it will retard timing resulting in a very unique pinging sensation from the engine. If you're experienced with it, you can easily tell the difference between the octane levels.

It also depends a lot on your climate and environmental conditions. If you're at altitude the 87 octane is just perfect even on the gen2. If you're never experiencing 90+ ambient temps (or heat soaking the engine) then the 87 is probably just fine as well.


The TL;DR: run whatever octane you want, but under certain load and environmental conditions the engine WILL retard timing which results in less effective power. For an easy demonstration on how important timing is, go unplug your VVT solenoids and drive around for a bit. You'll find it's super smooth but relatively gutless at certain RPMs.

 

[DanW]

The gen 1 is completely different than the gen 2.

Gen 2 increased compression and made that octane level an important factor. On the gen 1 it made very, very little difference. On the gen 2 you can feel an immediate difference with the higher octane under certain load conditions. On my 2020 JT it was a massive difference changing to just 89 octane. I personally recommend 89 for PUG 3.6Ls.

The reason it runs "smoother" is because the combustion cycle is properly completing at its targeted engine timing. If the engine begins to sense knock due to the lower octane, it will retard timing resulting in a very unique pinging sensation from the engine. If you're experienced with it, you can easily tell the difference between the octane levels.

It also depends a lot on your climate and environmental conditions. If you're at altitude the 87 octane is just perfect even on the gen2. If you're never experiencing 90+ ambient temps (or heat soaking the engine) then the 87 is probably just fine as well.


The TL;DR: run whatever octane you want, but under certain load and environmental conditions the engine WILL retard timing which results in less effective power. For an easy demonstration on how important timing is, go unplug your VVT solenoids and drive around for a bit. You'll find it's super smooth but relatively gutless at certain RPMs.

I have two gen 2´s, one with an auto, and one with a manual, and I cannot feel a difference with either of them between 87 and 93 octane. I´ve never owned a gen 1. And I run them hard, especially the JL with the manual transmission.

 

[Karlow17]

Does this sound like spark knock to anyone? Or something else? Only happens under load and with engine oil temp over 90C

 

[Wabujitsu]

Does this sound like spark knock to anyone? Or something else? Only happens under load and with engine oil temp over 90C

To my relatively uneducated, poor hearing - yes. After the engine is nice and hot, does it also “diesel“ when you turn the ignition off (continues to sputter and knock after shutdown)?

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