Run regular in 6.4 hemi

[JohnWedell]

Does anyone run regular in the 6.4 hemi. i will be going to Florida towing my fifth wheel and it would save a lot on gas if I could run it on regular instead of midgrade. They say you can use regular but recommended mid-grade.

[PlayersZ28]

Don't know about the 6.4 Hemi but the 5.7 in the Magnum wagon we had called for premium. I mostly ran regular and it just detuned the motor to accommodate any knock.

I would think when you're towing it'll be working harder and need the full power. You could try a tank full and see if you notice a difference.

Easier on the way to FL from NY as it's downhill

[Camper_bob]

I ran regular gas in my 6.4 Hemi for 3 years, no problem. Towing or not.

I tried to run mid-grade as much as possible, but didn't notice any difference, so I went with regular most of the time.

I did learn that you have to be careful what octane rating is considered "regular" based on where you are. There were places on our way to Colorado a couple years ago that "regular" meant 85 octane. "Regular" IMO means 87, plus or mid is 89, and premium is 91 octane. It was a little annoying going from "regular" to "plus" to get at least 87 octane fuel in the truck, and sometimes the price disparity was significant.

[spoon059]

Originally Posted by JohnWedell

Does anyone run regular in the 6.4 hemi. i will be going to Florida towing my fifth wheel and it would save a lot on gas if I could run it on regular instead of midgrade. They say you can use regular but recommended mid-grade.

From NY to FL is all flat ground (give or take 100' of rise or fall). I don't think you'll have any issues using the lower octane. The engine might detune or have minor knocking, but level towing won't strain it. If you were gonna climb the Rockies, I might put a couple tanks of higher octane for the ascent...

[DNelson]

I always run 87 octane in our 6.4. The few times I tried higher octane gas I couldn't tell the difference in either power or mileage.

[smurfs_of_war]

I have been running regular 87 in mine since I bought it from a crappy gravity fed farm tank. Towing or not, runs fine. Just finished a trip hauling a 3500 GM on a deck over 900km on 87.

[ttavasc]

Looks like 89 octane being recommended for the 6.4L started in 2015. The 1500/2500/3500 manual that came with my '14 1500 states 87 for both the 3.6L and the 6.4L engines and 89 for the 5.7L.

While I prefer to run the recommended 89 in my 5.7L there are times when we are out with the trailer and we run into a station with only 87 and 91 so I take the 87. Looking over my fuelly.com data for those tanks with 87 I don't really see any difference in fuel economy. In fact the last trip of this season I had some tanks of 87 through Idaho and into Utah - one ended up at 11.54mpg and the other at 13.98mpg.

The 2018 manual now includes the following language regarding the 87 octane in the 5.7/6.4L engines:

"While operating on gasoline with an octane number of 87,
hearing a light knocking sound from the engine is not a
cause for concern. However, if the engine is heard making
a heavy knocking sound, see your dealer immediately."

[PlayersZ28]

Originally Posted by ttavasc

"While operating on gasoline with an octane number of 87,
hearing a light knocking sound from the engine is not a
cause for concern. However, if the engine is heard making
a heavy knocking sound, see your dealer immediately."

Translation: A bit of tapping is just fuel quality, keep driving. A loud knocking is parts trying to move to where they shouldn't be. Visit your dealer sales department for further assistance.