Octane Question

[HAL9001]

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.

 

[Mountain Whiskey]

Come on. You can scroll past the first few threads. This same argument comes up every week. Some people think 87 is so bad the truck will implode on itself if near the same pump. Others see using over 87 as a colossal waste of money just empowering OPEC further.

Tap the little magnifying glass icon at the top and type octane in the blank. Prepare for amazement. With over 200 posts I would be certain you have read this 100 times.

Sorry for being a Richard,, I just couldn't help it.

 

[HAL9001]

Come on. You can scroll past the first few threads. This same argument comes up every week. Some people think 87 is so bad the truck will implode on itself if near the same pump. Others see using over 87 as a colossal waste of money just empowering OPEC further.

Tap the little magnifying glass icon at the top and type octane in the blank. Prepare for amazement. With over 200 posts I would be certain you have read this 100 times.

Sorry for being a Richard,, I just couldn't help it.

This is not yet another octane thread. I've read the general arguments of octane choices many, many times, but that is not what I'm asking here. My question is much more specific to a problem I'm having.

In normal use, my 1500 runs fine on 87 but when heavy towing it pings considerably, so obviously I can't use 87 then. I assume the pinging is normal when the 5.7 tries to pull a heavy loan when using 87 octane, but I can't be sure of that unless others tell me the same.

So, what I want to know specifically is if I need to use 89 or 91 for heavy towing and if so, do I need 91 or can I get away with 89?

I need to pull an 8,000-pound travel trailer thousands of miles yearly, so the cost difference between 87, 89, and 91 is significant especially with gas prices skyrocketing.

I was hoping that someone here who has experience heavy towing with the 5.7 Hemi can help.

 

[vincentw56]

Since 89 is recommended, you should be fine using it while towing and 87 any other time. You could also put in an octane boost if you already filled up although it might not get fully mixed.

 

[bigdodge]

Since 89 is recommended, you should be fine using it while towing and 87 any other time. You could also put in an octane boost if you already filled up although it might not get fully mixed.

best answer

because if you have ever seen an engine after a knocking failure you would make sure it knocks the least amount.

 

[vincentw56]

best answer

because if you have ever seen an engine after a knocking failure you would make sure it knocks the least amount.

That's why I won't run anything less than the recommended, but that's just me and how I feel.

 

[BowDown]

This is not yet another octane thread. I've read the general arguments of octane choices many, many times, but that is not what I'm asking here. My question is much more specific to a problem I'm having.

In normal use, my 1500 runs fine on 87 but when heavy towing it pings considerably, so obviously I can't use 87 then. I assume the pinging is normal when the 5.7 tries to pull a heavy loan when using 87 octane, but I can't be sure of that unless others tell me the same.

So, what I want to know specifically is if I need to use 89 or 91 for heavy towing and if so, do I need 91 or can I get away with 89?

I need to pull an 8,000-pound travel trailer thousands of miles yearly, so the cost difference between 87, 89, and 91 is significant especially with gas prices skyrocketing.

I was hoping that someone here who has experience heavy towing with the 5.7 Hemi can help.

When you are only driving with 87, the load isn't as great on the engine as it is when you're towing so you're hearing that in the form of pinging. Yes, If I were you, Id use 89 or higher when towing and 87, if its not causing you any knock problems during normal use.

 

[Mountain Whiskey]

Just had a really interesting trip towing my boat. I tow a 4000 pound pontoon - so say 5-6000 pounds loaded with gear gas and trailer - but the main issue is it’s a giant wind sail. 3.92 limited with e torque.

Anyway I left town, full tank of Costco 91 gas (because it’s cheaper than most other 89). Towed around 400km and averaged around 23L/100 (10 us mpg). Doing 110 the whole way, truck was almost always in 7th - sometimes even 8 - and no wind. I was pretty happy with this as my 17 was usually around 26-28 towing.

Stopped for gas in some ****hole town and only had 87 so I filled up anyway as it was shell at least. Within 5 minutes I noticed the truck wouldn’t go into 7 and was pretty much riding in 6 even 5 rest of the trip. Computer tells me I’m doing 28.5L/100 (8mpg). Stayed constant whole trip. Similar geography. No wind. Truck felt just weak and definitely used more gas. I can’t think of any other real variables that changed. I topped up with premium at around half a tank and it seems to be running better again but I’m only about 50k into this tank.

Anyone else notice this? Does 89/91 really perform this much better than 87 - especially towing?


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The truck is optimized for 89, but 87 is fine. However, you are putting more strain when towing, I would highly recommend you go with 89 or Costco 91 (since cheaper than regular 87) if you tow or are looking at the best performance for your engine.

I would run 87 if I was cruising along on the highway, but towing, go with 89 at least.

Firsthand experience - no. Understanding why this is - yes.

The knock sensors detected pinging so they retarded the ignition timing. Probably a lot. Retarded timing will cut the horsepower. Less horsepower means lower gears to move the load.

Yes, 89+ is the way to go for towing

Yup 89 for towing heavy loads, gives you the max HP/TQ. 87 is fine for normal driving

I tried 91 octane and got about 8-9 mpg pulling about 6000lbs total load. I could see 2mpg at WOT on the freeway accelerating tho!

I run 89 most of the time because I seem to be towing most weekends, or even tonight when I'm going fishing on the Mississippi with friends.

Like you said, pontoons are like pulling a sail and cause a lot of wind drag. It's not the weight at the wheel at that point but the additional power required to deal with the drag. When towing I sometimes run into the stations that only sell two types of gas - 87 octane with ethanol or 91 octane (non-oxy). I'll fill up enough to get to the next station and then get some 89 in there.

Even with 89 I'd bet it's knocking and pulling timing. When Towing I'd be putting 91-93 in.

I am not an engine expert, so don't take this as argumentative. However, don't you think Ram would advise owners to use 91/93 when towing if they felt that would extend the life of their product? I thought that to properly utilize higher octane fuels, the engine needed to be tuned for a higher detonation point.

It probably also depends on the load. There is certainly a difference between not towing, towing small boats/trailers, and towing close to the max towing capacity.

10.9:1 compression. That's a lot for 89 octane under stress IMHO.

The HEMI is 10.5:1 compression ratio.

89 octane fuel is recommended for optimum performance and fuel economy by Mopar.

Fuel Based On Compression Ratio

87 Octane
Gasoline with this octane number is proper for engines with compression ratios of 7:1 to 9:1.

89-90 Octane
Gasoline with this octane number is good for engines with compression ratios of 9:1 to 10:1.

93 Octane
Gasoline with this octane number is advisable for car engines with compression ratios of 10:1 to 11:1.

Based on this information our trucks will run optimally with 89-93 Octane fuel. Without having to advance or retard the timing.

From my experience, I have +1 MPG with Costco 91 comparing to 89 at Safeway or Arco. Since price is the same, Costco 91 is a no brainer.

When using any 87, I can hear a tick (not loud, but noticeable) when engine switches to 4 cylinder mode ("eco"), but it quickly disappears after filling the tank with Costco 91.

And yes, I really want to save ~$10 on every fillup (30-40 cents difference between 87 and 91 at Costco, filling 30 gallons into 33 gallon tank), but then I remind myself that it is a truck, it needs a lot of gas anyway, and I have Tesla Model Y in my garage for daily driving that consumes $9 of electricity for 300 miles of range.

You guys are convincing me to stick with 91! I save almost $30 a tank filling with Costco 91 vs shell 89 so that’s a no brainer, but next time I’m out on the road pulling I’ll spend the extra $10 for 91 instead of 89. It’s a 90k truck I really don’t mind spending $20-30 a month to keep it running better, and really if it even gets 1mpg better it’s basically a wash. If I really wanted to save money I could cut my speed by 10kph and save money that way. Or buy a Tesla.

Fun fact when I filled my truck it cost $120…..then I filled my boat for $400. Makes you care less about the 89 to 91 cost difference.


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Sadly it appears the answer is "no". FCA has made decisions that benefit it over us, the other major one being oil weight. We need to be running 5w-30 in our hemis but they need to get their corporate MPG up so they picked a watery oil to eek out a little better MPG.

Sometimes the politics or bean counters get in the way. No doubt the engineers would tell us what is best if they could, sometimes you need to read between the lines or look at past history/decisions or talk to other engineers etc.

My mileage 91 octane with 3.21 and 6600 travel trailer was 8 on the nose mountain driving 300 mile trip 70 mph. BUT, the 3.21 gears did great for all you doubters. Plenty of power The only weakness was the Falkens...too soft "wallowing" been there done that before and KO2'S solve that and only 900 bucks...on sale. Anyone want a deal on 20 inch falken AT's... great tire if you don't tow.

I was a huge believer in the 3.92 with my 2010 Ram and the 5 (really 4) speed transmission. With an 8 it’s basically obsolete and you’re just losing the extra overdrive of the 3.21 and the truck will find a gear to match any load between second and seventh with either diff. Nobody is struggling to pull anything in the first few gears that really necessitates the 3.92 anymore. I would have taken the 3.21 if it was available for me but it wasn’t a deal breaker either way. Just my opinion, but the 3.92 has been obsolete since the new transmission.


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My wife asked if something was wrong when we stopped on a hill at a stop sign. When we started to go with the 6000lbs loaded trailer, the tires squealed for quite a few feet as I pulled away gently. See sig line.

Pretty much been answered it seems. Stick to 89 or higher if under heavy load...otherwise 87 is fine for light duty driving.

As someone mentioned above, Sams/Costco 93 premium is typically close to 87 and cheaper than 89 at other stations. I do the mix method as well with tanks of regular and premium alternating.

Efficiency does go down a hair but not too bad. I lost about 1 mpg by switching to 87, and I don't fee a performance difference at all

Some people worry about the mpg loss of using 87. I was one of them so I did some math. I posted the following calculations in another thread, but here it is again in case anyone interested hasn't seen it.

If 89 cost $0.30 more than 87 (which is average here), how much better mpg do you have to get to offset the cost?

Octane	Cost per gal	mpg	miles	gallons used	Cost of trip
89	2.80	20.00	300	15.00	$42.00	actual	highway
87	2.50	17.85	300	16.80	$42.00	break even calc	highway
89	2.80	17.50	300	17.14	$47.99	actual	city
87	2.50	15.63	300	19.19	$47.99	break even calc	city

In the above chart I used 300 miles for a "trip."
I was averaging 20 mpg on the freeway and 17.5 around town when running 89. To figure out if 87 was less cost effective I calculated what my mpg would have to be to cost the same (or worse).
I highlighted the calculated values in red to show where the break-even point is. If I use 87 and lose more than about 2 mpg I'm actually better off running 89.
I am currently averaging 16.7 around town, and that's with the slightly bigger tires, and lift/level. So that 0.8 mpg loss may not be entirely a result of the octane change. Even if it is, I'm still well ahead of the break even mark. No reason at all for me to run 89.
Just something to consider.

Welcome to the forum . Generally speaking the Hemi is ok on 87 octane but is recommended 89 octane . I've run 87 , 89 and 91 with no noticeable difference in performance . I don't think you would have to worry about any damage unless it's been pinging and/or knocking a lot . I think once you switch to the higher octane you'll be fine .

There's no reason to go to 91. I'm not sure what's available in your area, but you'd be fine with 87 or 89 octane. From what I've read, 85 at altitude is like 87 at sea level. Does the noise go away with higher octane fuel? If so I wouldn't worry about it. If not,

Run a few tanks of premium 91 through there. If the ping noise goes away, then thats your proof your engine wants something better than 85. It takes a few tanks to get all the "old" gas out of there, so don't get frustrated if you have no results after the first tank of 91.

Every engine can be different. I'm doing the same thing with mine right now. Mine seems to hate ethanol more than most, which is in most fuels up in my area, even Costco. I used to run 91 with 10% ethanol usually (Costco), and she will ever so slightly ping under moderate throttle if I hit the right RPMs/speed, usually merging onto the highway. I started running 91 non-ethanol (only 1 tank so far) from a different station, and after two or three tanks, we'll see if there is a difference. I know my MPG is up by about 0.5-1 (in city), which I expected, as ethanol hurts your MPG as well.

Owners manual calls for 89 use 89. No reason to spend more money on premium.

If you’ve been letting this happen for a while under moderate to high loads, then you probably have some minor pitting on the pistons and valves from detonation; however, it’s not the end of the world. Just move the octane up to the next higher rating and see if it resolves it.

After reading a couple posts. It seems the general consensus is trucks run fine on 87. Some people like to run 89 because it makes them feel good.

Trucks under load may ping using 87. Switching to 89 may help. Trucks computer is not programmed for 91 so it does nothing.

If more power is needed under load, unlock the PCM and get a tune. Truck will run better all around. Warranty will be voided though.

So the real answer after reading weekly postings is...... It all depends.....

 

[djevox]

Did your typing finger just have a stroke, or did you mean to reply to every person in the thread?

 

[theblet]

After reading a couple posts. It seems the general consensus is trucks run fine on 87. Some people like to run 89 because it makes them feel good.

Trucks under load may ping using 87. Switching to 89 may help. Trucks computer is not programmed for 91 so it does nothing.

If more power is needed under load, unlock the PCM and get a tune. Truck will run better all around. Warranty will be voided though.

So the real answer after reading weekly postings is...... It all depends.....

If more power is needed under load (towing) run 89, no need for a tune. Otherwise 87 is fine.

 

[UnloosedChewtoy]

Just to update you all, I have confirmed... 91 octane (no ethanol) after a few tanks has completely eliminated any pinging. I would run lower octanes, like 89, but they do not offer that ethanol-free in my area. Only ethanol free octane is usually 91.

I really wish our Costco was like many others I've seen in other states, which offered an ethanol-free option. It will hurt the wallet a bit, but no more Costco ethanol laced stuff for the truck.

So again, if you want to test if its the octane or ethanol causing ping, try some 89 or higher ethanol-free gas for at least two or three tanks.

 

[devildodge]

I have been running 88 Octane. I haul at GVWR often and tow my camper. It was 20 cents cheaper...but right now rutters and Sheetz are having a gas war with it I guess. Sheetz went to 25 cents cheaper...just saw rutters is 26 cents cheaper

It is what I will be using for now on..both towing and normal driving.

 

[theblet]

I wish we had gas wars around here.

 

[HAL9001]

After reading a couple posts. It seems the general consensus is trucks run fine on 87. Some people like to run 89 because it makes them feel good.

Trucks under load may ping using 87. Switching to 89 may help. Trucks computer is not programmed for 91 so it does nothing.

If more power is needed under load, unlock the PCM and get a tune. Truck will run better all around. Warranty will be voided though.

So the real answer after reading weekly postings is...... It all depends.....

Thank you very much for compiling these answers. You were right, I should have searched first!

 

[HAL9001]

Thanks to all who took the time to reply. I'll switch to 89 and see if the pinging stops when towing. Hopefully that should solve the issue. I'm just glad it's not something wrong with the engine.

 

[Mr.Grid]

I’m towing across WV / VA Tuesday with enclosed 7k# car hauler and new 1000 mile Hemi. Doing the same as I did with my 2011 Hemi and it’ll be with 93-91. Better mileage and power compared to when I used 89 octane in that truck towing. The difference in fuel cost is less than 30¢ a gallon. When not towing I’ve always used 87 -89. I only purchase Top Tier gas when possible.

 

[Neurobit]

If you drive a lot of miles, 89 is a good compromise without breaking the bank.

 

[Mr.Grid]

I have been running 88 Octane. I haul at GVWR often and tow my camper. It was 20 cents cheaper...but right now rutters and Sheetz are having a gas war with it I guess. Sheetz went to 25 cents cheaper...just saw rutters is 26 cents cheaper

It is what I will be using for now on..both towing and normal driving.

View attachment 111048

How much Ethanol is in that 88 octane…… 15% ?

 

[devildodge]

How much Ethanol is in that 88 octane…… 15% ?

Yes up to 15%. So quite possibly the same as E10 lol

 

[Shark875]

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.

I actually started to run only 89 in mine as well, I noticed I seem to get better fuel economy so I waive the additional .15- .20 cents extra per gallon. The Hemi definitely like to drink the higher octane fuel better