3.6 engine and 87 octane a no-no

[Petey]

So you're saying the difference in octane rating between diesel and gas are the reason a diesel won't run on gas?

BTW octane does not affect air/fuel ratio.

on rare occasions diesels apparently can run on gas to a certain degree ...original diesel was a mix of oil and gasoline 50/50....however , doesn't mean one should ... octane saves me from a poor AFR I don't see where your latter statement has to do anything directly with what I said .

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[Soggybottomboy]

Poor Petey has been jousting at this windmill since 2020. I don't believe his logic, but I am extremely impressed by his total commitment to it.

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[bmpcamry09]

Love me a good octane thread. Amazing how many people don’t truly understand what high octane is for and what it actually does.

I always tell people to stand on a sidewalk near a stop sign for a few hours and listen to how 90 percent of modern DI/turbo cars run as they pull away. You can always tell which ones put 87 octane in the middle of 100 degree weather because they all ping like mad on tip in.

The same people that will scream “but the owners manual says 87”. Sure it’s okay, but most modern ECUs “sniff out” the highest spark possible and have both high octane and low octane spark tables. They will ride that knock sensor to get the most advance possible and when knock is picked up, they will use a knock modifier of sorts to make it “safe” for 87 octane.

Even my basic cars get 89 minimum for this exact reason, but if tuned/turbo/forced induction, I put the highest at the pump.

 

[cripton805]

I haven't read the entire thread.

Higher Octane fuel reduces the likelihood of Pre-ignition in the cylinder. Compression can Pre-Ignite the fuel before the spark plug properly produces a spark at the right timing. Higher Octane fuel also reduces the likely hood of Detonation "aka Knock" due to heat, compression, load, etc.

Utilizing the proper Fuel Octane Rating provides peak performance (especially under load), has less chances of Pre-ignition or Detonation, and provides slightly better mpg. "ONLY" if the vehicle was designed for that specific Fuel Octane Rating.

**My Opinion on the 3.6L Pentastar**
I believe that this engine "can" run on Regular 87 Octane fuel and the knock sensor will retard the timing as needed. Although, due to its High Compression, a lot of people will experience different outcomes. In hot weather, towing, adding weight, not regearing diff, large tire / wheels, etc.

If you're just driving on the highway and your Jeep is completely stock and you're not running it hard. You may possibly get by with running 87 Octane rated fuel. If you're running your rig at 90+ Degrees Fahrenheit, crawling steep hills, pulling a trailer, running 40s on stock gears, have a rooftop tent, steel bumpers / rock rails, etc. You should probably run 89-93 Octane. Would the knock sensors kick in running 87 Octane? Yes they will, but why would you want to stress your engine and have less performance?

Hope this helps.

 

[bmpcamry09]

I haven't read the entire thread.

Higher Octane fuel reduces the likelihood of Pre-ignition in the cylinder. Compression can Pre-Ignite the fuel before the spark plug properly produces a spark at the right timing. Higher Octane fuel also reduces the likely hood of Detonation "aka Knock" due to heat, compression, load, etc.

Utilizing the proper Fuel Octane Rating provides peak performance (especially under load), has less chances of Pre-ignition or Detonation, and provides slightly better mpg. "ONLY" if the vehicle was designed for that specific Fuel Octane Rating.

**My Opinion on the 3.7L Pentastar**
I believe that this engine "can" run on Regular 87 Octane fuel and the knock sensor will retard the timing as needed. Although, due to its High Compression, a lot of people will experience different outcomes. In hot weather, towing, adding weight, not regearing diff, large tire / wheels, etc.

If you're just driving on the highway and your Jeep is completely stock and you're not running it hard. You may possibly get by with running 87 Octane rated fuel. If you're running your rig at 90+ Degrees Fahrenheit, crawling steep hills, pulling a trailer, running 40s on stock gears, have a rooftop tent, steel bumpers / rock rails, etc. You should probably run 89-93 Octane. Would the knock sensors kick in running 87 Octane? Yes they will, but why would you want to stress your engine and have less performance?

Hope this helps.

Yep. Good stuff.

Developing tuning on these I learned how aggressive the spark maps are. They are very aggressive. 87 octane barely works in the 3.6. It’s constantly having to pull timing on 87. Even tuning for 93, the most extra timing I could add in the tune comfortably was 3-5 degrees depending on where in the curve it was.

 

[jbcrane]

Yep. Good stuff.

Developing tuning on these I learned how aggressive the spark maps are. They are very aggressive. 87 octane barely works in the 3.6. It’s constantly having to pull timing on 87. Even tuning for 93, the most extra timing I could add in the tune comfortably was 3-5 degrees depending on where in the curve it was.

Thanks for the additional information/confirmation.
I don't care what anyone says, especially the owner's manual who - because of ESS - has proven beyond any doubt they're not interested in my engine's longevity. Every car I've had runs the highest octane I can find, which here in Colorado is 91. And it's always top tier - preferably Shell. Doing anything different is adding to potential problems developing and that's just no bueno. And I always change my oil long before it's due. My cars have routinely lasted a long, long time.

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