1500 hemi towing with 87 vs 89octane

Has anyone tested their towing mpg with these two octane rated fuel? I'm curious to know if it's worth the extra 8bucks to add 89octane when towing. We will be going on a 3200km round trip in July so I'm hoping to see if its worthwhile running the mid range fuel.

Historically, we get around 8-9mpg towing a 6000# 25ft travel trailer with our 2017 1500 5.7 8spd 3.21 with at 276/65/20LT.

Gero said:

Has anyone tested their towing mpg with these two octane rated fuel? I'm curious to know if it's worth the extra 8bucks to add 89octane when towing. We will be going on a 3200km round trip in July so I'm hoping to see if its worthwhile running the mid range fuel.

Historically, we get around 8-9mpg towing a 6000# 25ft travel trailer with our 2017 1500 5.7 8spd 3.21 with at 276/65/20LT.

Click to expand...

I'm not concerned about MPG when towing, and you're drinking so much fuel with that trailer that any tiny gains you get from octane will be completely offset by the brick you're pulling.

But I'd never tow with < 91 octane, because for best performance (no pinging) especially for hours on end at high temps its going to be better for the engine to burn the fuel it really wants.

The way these engines are tuned, they "want" 89 but will fall back to a lesser tune when they detect knocking on 87. Even with 89 it's not enough on the crummy gas we have in my area, 91 it still does it a bit.

I run 91 all the time these days. The engines come with short term trim tables and long term trim tables and I could be wrong but it seems to do the best on 91 permanently. Otherwise it gets confused as it bounces around from octane to octane before the long term tables get updated. If you keep it 91 then its ready to tow at all times as well instead of having half 87/89 or whatever.

So no, I don't think its worth it or noticable from a MPG perspective but my truck definitely pings on the lower octanes and I'd never tow a heavy load when its doing that.

Just my 2 cents.

ramffml said:

I'm not concerned about MPG when towing, and you're drinking so much fuel with that trailer that any tiny gains you get from octane will be completely offset by the brick you're pulling.

But I'd never tow with < 91 octane, because for best performance (no pinging) especially for hours on end at high temps its going to be better for the engine to burn the fuel it really wants.

The way these engines are tuned, they "want" 89 but will fall back to a lesser tune when they detect knocking on 87. Even with 89 it's not enough on the crummy gas we have in my area, 91 it still does it a bit.

I run 91 all the time these days. The engines come with short term trim tables and long term trim tables and I could be wrong but it seems to do the best on 91 permanently. Otherwise it gets confused as it bounces around from octane to octane before the long term tables get updated. If you keep it 91 then its ready to tow at all times as well instead of having half 87/89 or whatever.

So no, I don't think its worth it or noticable from a MPG perspective but my truck definitely pings on the lower octanes and I'd never tow a heavy load when its doing that.

Just my 2 cents.

Click to expand...

I've used 89 and 91 before and I really can't notice anything other than the psychological aspect. Burning 30L/100km means refuel every 300km which is very annoying even with a 121L tank. But I guess this is the trade off for not having to deal with DEF of then diesels.

Gero said:

I've used 89 and 91 before and I really can't notice anything other than the psychological aspect. Burning 30L/100km means refuel every 300km which is very annoying even with a 121L tank. But I guess this is the trade off for not having to deal with DEF of then diesels.

Click to expand...

I see you're in ON as well, nice!

I pull a very similar load to you, almost same length at 6000 pounds, 8 foot wide dual axle. If I keep my speed at 103 km/h, with light or moderate wind (typical summer day in ON) I can usually get about 10 to 11 mpg? If the light wind is behind me its closer to 12. If the wind is in front I can drop to (worst) 8.

Most often my gauge is saying 10 mpg (22 l/100 km).

As soon I get in a hurry the mileage drops severely. So if you can take it slower that will probably save you more fuel than the 91 octane, but honestly I'd run the high octane anyway.

And agreed, all gassers seem to drink fuel when towing but I'll take it any day over diesel issues, guys being without their truck for weeks/months waiting on parts etc. My cousin's husband has a GM 6.6 duramax and his was gone for 3 months at < 6 months of ownership waiting on parts. That would drive me nuts, all covered under warranty and they gave him a 1500 as a rental but he has a business and needs to tow heavy too.

Gero said:

Has anyone tested their towing mpg with these two octane rated fuel? I'm curious to know if it's worth the extra 8bucks to add 89octane when towing. We will be going on a 3200km round trip in July so I'm hoping to see if its worthwhile running the mid range fuel.

Historically, we get around 8-9mpg towing a 6000# 25ft travel trailer with our 2017 1500 5.7 8spd 3.21 with at 276/65/20LT.

Click to expand...

Yes, it's worth it. Especially, going uphill with those gears.

If you can't afford the $ you shouldn't go.

I've been as low as 6 mpg with a headwind in Texas.

ramffml said:

The way these engines are tuned, they "want" 89 but will fall back to a lesser tune when they detect knocking on 87.

Click to expand...

^^^ this
Pre-detonation and lugging the engine can destroy an engine while towing. Use fuel with enough octane and enable the Tow/Haul mode to mitigate the issues.

ramffml said:

I'm not concerned about MPG when towing, and you're drinking so much fuel with that trailer that any tiny gains you get from octane will be completely offset by the brick you're pulling.

But I'd never tow with < 91 octane, because for best performance (no pinging) especially for hours on end at high temps its going to be better for the engine to burn the fuel it really wants.

Click to expand...

My manual states:

6.4L ENGINE

Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine.

This engine is designed to meet all emissions
regulations and provide satisfactory
fuel economy and performance when using
high quality unleaded gasoline having a
posted octane number of 87 as specified by the
(R+M)/2 method.

No other recommendation other than 87 octane. It doesn't even say "at least" 87 octane - just 87 octane.

Tulecreeper said:

My manual states:

6.4L ENGINE

Do not use E-85 flex fuel or ethanol blends greater than 15% in this engine.

This engine is designed to meet all emissions
regulations and provide satisfactory
fuel economy and performance when using
high quality unleaded gasoline having a
posted octane number of 87 as specified by the
(R+M)/2 method.

No other recommendation other than 87 octane. It doesn't even say "at least" 87 octane - just 87 octane.

Click to expand...

You have the 6.4. It has a different compression ratio, different tune. I haven't towed with the 6.4, but my comments were with respect to the 5.7.

I can't speak for the newer 5.7's. My FIL had an '03 2500 with the 5.7, manual said run '87 minimum.

I had my 6.4, and I ran it for 3-4 years on '91/92 (depended on what station I was at, my '17 manual said run '89 minimum but that stuff SITS in the tanks around here so no telling how old/degraded it is) and it ran great. Switching to '87 when they jumped the price of premium but left regular alone (price differential is now something like $1.25 here, more at some stations), I saw no loss in mileage or power, and no noticeable knocking, so I'm sure the computer compensated for it. The first few tows of the camper I switched back to premium, then I forgot a couple times and still saw no issues towing with '87, even on 3-4 hour (250-350 mile) hauls at 65 mph. I also saw no real difference in mileage while pulling on the two different grades of gasoline.

If I were going to be pulling >50% of the time with a gas motor, yes, premium (91/92 octane) would be the way to go, just for added peace of mind if nothing else. For the occasional haul, I would say it's up to you. I personally had no issues but that doesn't mean you won't, though it also doesn't mean you will.

I always run 91-93 oct when I plan on towing and I wouldn't run anything less than 89 oct recommended in the owners manual, again, when towing.

ramffml said:

You have the 6.4. It has a different compression ratio, different tune. I haven't towed with the 6.4, but my comments were with respect to the 5.7.

Click to expand...

I should have clarified that I meant to just go by what the owners manual recommends. I don't know what the manual says to use for the 2017 RAM 1500.

My manual for my 2013 5.7 states regarding 89 octane fuel: "...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. The manufacturer recommends the use of 89 octane for optimum performance. The use of premium gasoline is not recommended, as it will not provide any benefit over regular gasoline in these engines." So, if I'm just cruising around town I typically put in 87. If I'm going on a camping trip and towing my camper, I put in 89 or 91.

Gero said:

Has anyone tested their towing mpg with these two octane rated fuel? I'm curious to know if it's worth the extra 8bucks to add 89octane when towing. We will be going on a 3200km round trip in July so I'm hoping to see if its worthwhile running the mid range fuel.

Historically, we get around 8-9mpg towing a 6000# 25ft travel trailer with our 2017 1500 5.7 8spd 3.21 with at 276/65/20LT.

Click to expand...

I tried it... made absolutely no difference. I run 87 octane all the time. My 2014 pulled about the same sized trailer over 25,000 of the 100,000+ I drove it before trading on a 2024. MPGs were the same as yours (8-9 depending on conditions).

I have never any pinging or pre-detonation from any of the 3 5.7s I've owned. When I drag my trailer its usually 70+ mph.
Heck, even my snowmobiles have knock sensors that will retard timing if/when pre-detonation is detected (those motors require 91+ to run right).

What really affects the MPGs are
1. Speed
2. Wind
3. Winter vs Summer blend gasoline (winter is lower MPG)

IMHO you're wasting your money.

when i tow, i put 91 marine fuel in my boat. oh and 87 in the truck.

Put me in the camp for higher octane fuel while towing. I live less than 5 miles from work, so I run either 93 octane E10 or ethanol-free 90 octane fuel. I have a hemifever tune, so that makes a difference on my choice of fuel. There is a noticeable difference in torque while using 93, compared to 89. I notice this mostly after burning one tank of fuel. I believe that my engine is pulling too much timing with 89 or lower fuel. That is mostly a result of the tune that I am using.

From my understanding, the timing algorithm for 89 octane is default, meaning that that timing is baseline unless the knock sensors detect preignition. Once knock is detected the ECM will switch to another algorithm for 87 and will continue to pull back timing if necessary, if knock persists, to a max retard limit set by the ECM. Switching time is in milliseconds from knock detection.

I do not know what the timing differential is in degrees between the 89 and 87 timing algorithms, and I think this value is different for different years.

In theory advanced timing without knock should produce more power, but under actual conditions any marginal difference is likely to be unobservable because it is masked by engine load.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, 18” wheels. Build Date: 3 June 2018. Now at 111890 miles.

Same year and truck configuration as the OP. My travel trailer is around 6700 lbs. 10-11 mpg on our recent trip from SC to central NY by way of the hills in TN and KY. I run 89 all the time and tow at 65 max.

I once compared 87 to 89 on my old Expedition towing. Mileage was better on 89 but not enough to make up for the difference in price. I stick with 89 on the Ram cause it's tuned for it

2018 6.4 with close to 200,000 mi and most of it was 85 octane, 2022 with over 50k mi and 87 and 85.

Gero said:

I've used 89 and 91 before and I really can't notice anything other than the psychological aspect. Burning 30L/100km means refuel every 300km which is very annoying even with a 121L tank. But I guess this is the trade off for not having to deal with DEF of then diesels.

Click to expand...

I thought the same, but MAN! I miss my 06 5.9 CRD

When I first got my 22, it was new years. I ran 87 that winter and 89 in the spring. Since then it is 89 all the time here. Manual implies that is what the 5.7 is designed for. I’ll just use it.

When towing, I might top off with 91, but not always. It depends on the difference in price and if I’m on E, lol.