Octane / Towing

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HAL9001

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I have a 2021 1500 Limited with the 5.7 Hemi. With the skyrocketing cost of gas, I've been using 87 octane gas (regular). I sometimes get occasional very light knocking only when the engine is in ECO mode (MDS) but other than that it runs great.

However, when I recently tried to pull my travel trailer that weighs around 8,000 lbs for the first time, I got moderately heavy knocking during acceleration. This of course is unacceptable. The owner's manual states:

"This engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high-quality unleaded gasoline having an octane range of 87 to 89 as specified by the (R+M)/2 method. The use of 89 octane “Plus” gasoline is recommended for optimum performance and fuel economy".

So, it's rated to run on 87 octane but 89 (mid-grade) is recommended. I'll switch to 89 when towing the trailer and hopefully, that will cure the knocking.

Has anyone else seen this issue when pulling a heavy trailer? Will 89 be enough or do I need to switch to 91 octane (premium) for towing?

Any insight is appreciated.
 

MADDOG

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It really depends on temperature, percent grade and GCVWR. If it's hot, hilly and you are close to max combined weight you may find 91 octane will work better.

If it's not as hot, not as steep or you aren't near your max GCVWR then you can try 89.

My 6.4L did fine on 87 when not towing. Add a load to that truck and it pinged quite a bit. I just went right to 91 and the pinging pretty much stopped. I'd get a little on the steepest grades during the hotter summer days.
 

IdahoDen

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I have a 2021 1500 Limited with the 5.7 Hemi. With the skyrocketing cost of gas, I've been using 87 octane gas (regular). I sometimes get occasional very light knocking only when the engine is in ECO mode (MDS) but other than that it runs great.

However, when I recently tried to pull my travel trailer that weighs around 8,000 lbs for the first time, I got moderately heavy knocking during acceleration. This of course is unacceptable. The owner's manual states:

"This engine is designed to meet all emissions regulations and provide satisfactory fuel economy and performance when using high-quality unleaded gasoline having an octane range of 87 to 89 as specified by the (R+M)/2 method. The use of 89 octane “Plus” gasoline is recommended for optimum performance and fuel economy".

So, it's rated to run on 87 octane but 89 (mid-grade) is recommended. I'll switch to 89 when towing the trailer and hopefully, that will cure the knocking.

Has anyone else seen this issue when pulling a heavy trailer? Will 89 be enough or do I need to switch to 91 octane (premium) for towing?

Any insight is appreciated.
Although octane rating may make a difference when pulling a trailer of that weight, I think your biggest issue is pulling a trailer that is 80% of your towing capacity. Obviously at that weight it has some size to it so you were also increasing wind drag as well. We had a 2014 1500 Longhorn with the 5.7 L engine and when towing our 2 horses with tack, we were pulling about 5500 pounds. When going up hills and over passes we could really feel the load. So I cannot imagine what it’s like pulling an 8000 pound trailer, bigger in size, with that same engine. Most of all, remember going downhill, you have weight behind you that’s almost twice the weight of your vehicle pushing you downhill.
 

69GWC

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I run 91 when I know I am going to pull anything and never have a problem.
If I know Iam just going to burn a tank of gas running down the hwy I will run 87.
 

Wyo72

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Pretty hard to find 89 around here, most stations have 85, 87, and 91. There are a couple that have 88 which is what I run most of the time. Usually when towing my camper I run 91 but with prices the way they are not sure thats going to happen this summer.
 

MateoQueFeo

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If lower octanes are preferred for higher elevation driving, does that also hold true for towing?
 

msedly

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If I know I'm going to be pulling anything substantial I always use 93. A few thousand pounds or less and 89 seems to be fine.

I like to run 89 all the time but I've been using 87 lately with fuel prices being as bad as they are. I don't regularly tow anything over 1k lbs so it works alright. With 87 I notice a little knock when it's hotter out and I'm in the throttle more than 25% or so.
 
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HAL9001

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Although octane rating may make a difference when pulling a trailer of that weight, I think your biggest issue is pulling a trailer that is 80% of your towing capacity. Obviously at that weight it has some size to it so you were also increasing wind drag as well. We had a 2014 1500 Longhorn with the 5.7 L engine and when towing our 2 horses with tack, we were pulling about 5500 pounds. When going up hills and over passes we could really feel the load. So I cannot imagine what it’s like pulling an 8000 pound trailer, bigger in size, with that same engine. Most of all, remember going downhill, you have weight behind you that’s almost twice the weight of your vehicle pushing you downhill
I've towed this trailer from VT to FL and then back again and had no issues. I resolved the pinging problem simply by going to 89 octane. In tow/haul mode the engine had no issues even with steep hills. On the highway I averaged 65mph with no problem and could have even pushed it to 70 which I did now and then when passing tractor trailers. I never felt a lack of power and was highly impressed with the performance of the 5.7. My specific 2021 5th Gen is rated to haul over 12,000 lbs so an 8000 lb trailer is well within its capability.
 

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I will sometimes use mid grade if towing on a high heat day but normally use regular. our trailer is 6000# 28' travel trailer. I have never put 91/93 in the truck and it has always seemed to run fine. as for using 91/93 in higher elevations, folks on rv sites say low grade better because of thinner air. when towing in S.D. and wyoming I still run low grade , usually 85.
 

MateoQueFeo

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Why wouldn't you treat high heat days the same as high elevation - high heat makes the air "thinner".
 

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I never thought of that. just have always heard it's better to run higher octane. in the mountains regular is 85 so evidently it works for the locals.
 

Grand Mesa

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If lower octanes are preferred for higher elevation driving, does that also hold true for towing?

Yes, 85 octane is all that's available here other than diesel. Next available gas is 50 plus miles away. It has zero issues towing heavy trailers including vehicle transport trailers up 10% plus grades on 85.
 
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HEMIMANN

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What's your definition of "enough"?
You could tow heavy with low octane gas if you keep in 1st gear and go 20 mph.

If you want the performance the truck was intended for, including tow weight, then 89 octane and limit overdrive. There are octane boost additives you can buy if 89 isn't available.
 

runamuck

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funny tho..I have gotten as much as 21-21.5 driving in the higher elevations while about 20 is my usual high in the flatlands and the truck seems to run really well. of course I have not towed in the high elevations yet. I will find out about that next week as we are towing from DFW to colorado springs and I cant wait to pay 4.50 for gas. uphill all the way from here so I expect around 8 mpg.
 

HEMIMANN

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funny tho..I have gotten as much as 21-21.5 driving in the higher elevations while about 20 is my usual high in the flatlands and the truck seems to run really well. of course I have not towed in the high elevations yet. I will find out about that next week as we are towing from DFW to colorado springs and I cant wait to pay 4.50 for gas. uphill all the way from here so I expect around 8 mpg.

Hey, maybe the lower air density reduces pressure drag on the vehicle body enough to overcompensate for leaner combustion air? I don't know, just throwing the physics out there for musing.
 

Grand Mesa

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funny tho..I have gotten as much as 21-21.5 driving in the higher elevations while about 20 is my usual high in the flatlands and the truck seems to run really well. of course I have not towed in the high elevations yet. I will find out about that next week as we are towing from DFW to colorado springs and I cant wait to pay 4.50 for gas. uphill all the way from here so I expect around 8 mpg.

I just filled up 20.5 gallons of 87 ethanol free gasoline into jugs for use in our ranch equipment. $5.099 per gallon at a Maverick in Clifton, Colorado. Cheapest around for 87. The Front Range usually offers cheaper fuel than on the Western Slope.
 
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runamuck

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I just checked in woodland park as we are headed up there and the going rate is 4.60 for regular. I tend to check a few places before I head out when towing. looks like mostly 4.30 along my route. I figure 8 mpg when towing just to be safe and with 33 gal tank I look at 250 mile stops. I also google earth a few stations to make sure they are easy in easy out for me and my 28' trailer.
 

HEMIMANN

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I just filled up 20.5 gallons of 87 ethanol free gasoline into jugs for use in our ranch equipment. $5.099 per gallon at a Maverick in Clifton, Colorado. Cheapest around for 87. The Front Range usually offers cheaper fuel than on the Western Slope.

Don't forget to add storage stabilizer to it. Then you're good for up to two years.
 

Grand Mesa

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Don't forget to add storage stabilizer to it. Then you're good for up to two years.
Yes, right when I got home it got STA-BIL. Got 45 gallons of gasoline and 30 gallons of propane in storage out in an old pole barn. Our rural mountain electric company went green. After our first power outage at negative 23F we purchased a dual power generator.
 
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