Fuel type when towing

For those of you who tow what grade fuel do you use? Normally i use 87 without towing anything. Just curious if it is any difference to switch to a higher grade fuel.

 

I use 87 when towing

 

87 all the time.

 

The truck doesn't make any use of a higher octane, 87 is good for anything from tooling around town and heavy towing. Actually running higher octane than a manufacturer calls for is just throwing money in a hole.

 

87 gets the job done. Only time you'd need higher is if you have a SC

 

Alright great. I was curious if it made any difference so i guess I'll just stuck with the 87

 

Your truck is tuned for 87. Use 87, towing or not.

 

Old thread revival,

I was scouring the forum and this fit the bill without starting a new thread. I pull my Toyhauler (6600lb empty) regularly; in-state trips, 600 mile trip this past weekend, and 1900 miles last month. I have always run 87 octane, towing or not. I was (until today) a firm believer in "just run the minimum octane the manufacturer recommends".

The trip:
-Beaufort NC- Mount Pleasant SC (round trip)
-Same cargo each way, same weight, same toys, no water or waste in any tank.
-Same route, same weather, same driving conditions.
-I try to maintain 65-68 mph, seems to be where the Tundra is happiest towing.
-Tow haul On, manual shift mode 5.
-Trip down 87 octane, 10% ethanol. 7.8MPG
-Return trip, 89 Non-ethanol 1st stop, 89 10% ethanol 2nd stop. 8.5MPG


Much more than an MPG observation:
-The truck likes to hunt for gears when pulling, obvious and documented. The slightest movement of the gas pedal when cruising between 65-68 will downshift from 5th to 4th. Asking the truck to accelerate at an increase of more than 1mph per mile will always be returned with a downshift to 3rd.
-The trip to SC was normal, truck would cruise in 5th for a while, then 4th for a while, with bursts of 3rd thrown in whenever it wanted to go there. This was all on 87 octane fuel.
-The return trip was nothing short of amazing, 89 octane with one stop being non-ethanol. Gas light was on when I filled up before we returned home this morning. I based my observation on the fact that I was rolling along in 5th gear for an abnormally long time without a down shift. The reduction in shifting from 5th to 4th was unbelievable. The engine was completely content making decent power under 2500. I was humming along in 5th gear TC locked for the entire length of SC31 around Myrtle. I started to play around with the throttle a little, applying throttle to encourage a downshift. The truck was able to accelerate, slowly, in 5th gear without calling for a downshift. If I applied more throttle it would still induce a downshift to 4th. The truck only reached 3rd on the causeways/bridges, never under normal cruising/accelerating conditions.
-I filled up with 89 in SC because it was non-ethanol available at the station. I filled up with 89 for the 2nd tank just to confirm what I was feeling.

Questions:
-Anyone else out there notice something similar?

-Anyone out there with tuning knowledge on the Tundra? Is the Tundra able to real-time adjust it's timing and shift logic to mitigate detonation under different loads while running different octane fuels @dirtydeeds ? This is the only way I could understand what I imagine was happening. The truck realized, with 89 octane fuel, it was not detonating in a Low RPM/High Load situation and just kept chugging along.

 

No matter how many anecdotes you throw at it, or how many threads you start or resurrect, if your truck is tuned for 87, running a higher octane does nothing, nada, zip, zilch. Its primary effect is the faster draining of your wallet.

No seriously, I don't care, it doesn't help. And did I mention it does nothing??

because science.

Now all that said, the difference you noted could be attributable to a lot of things, Better gas, relative difference in ethanol content, humidity, altitude change, wishful thinking, all could play a part.

 

Ethanol is TERRIBLE for gas mileage. You would've probably seen close to the same gains between 87 10% and 87 0% (do they even make this?)

 

A couple comments. First, here in Texas, many of the Murphy USA stations at Walmart are selling 87 non-ethanol. I use it in my boat. Some of the Buc-EE's also sell non-ethanol, in regular and premium grades.

Second, while bobeast says the truck is tuned for 87, he's correct to a point. Thing is, the 5.7L (like many other modern engines) is "governed" to 87 octane (for lack of a better word) by the knock sensor. In other words, it will run just fine on 87 octane because when it DOES start to show signs of detonation (detonation that you can't perceive, and it WILL, more than you might think), then the knock sensor will retard the timing. By doing so, it stops any detonation, but consequently detunes the engine, lowering HP, worsening gas mileage.

I have tested the difference between 87 octane ethanol-laced gas and 93 octane ethanol-laced gas. I live in fairly hilly country and being retired and living 20 miles from the nearest small town, am in no hurry to get around (I drive to town doing 60 usually). I get 1½ MPG better mileage with the 93 octane than with the 87. Consistently. Ran the test for a year. Summer and winter. Also had the same results as @OBXTundra in the way the truck reacts to hills, pulling, downshifting, etc.

Came to the conclusion that for regular driving, the MPG increase didn't justify the increase in cost per gallon. Would have to get 23 MPG average to equal the same cost/mile.

But when I pull 4500# of boat 280 miles to the gulf coast (and back) in 100°+ weather, I DO use the 93 octane. The 5.7 just doesn't have to work as hard, has more power, doesn't have to downshift nearly as often, and is much smoother overall.

 

@Ericsopa this is exactly what I've found while browsing the web this AM. I don't think there is a benefit to running higher octane all of the time. But for towing I believe it does make sense. Primarily because the engine is operating in the peak knock-zone of the RPM range most of the time. Thanks for the post and your experience.

The 5.7 is known to show symptoms of detonation in different climates, elevations, and driving situations. This is documented here and many other forums. But, the truck will run perfectly fine on 87 octane almost all of the time, thanks to the knock sensor. I wouldn't say that my truck ran "bad" while towing on 87 octane, but it ran better and shifted much less running on 89. This was not in my head and there were no other factors at play. An engine that might have detonation symptoms under average driving conditions will have them accentuated under towing/high load situations. What I experienced was the PCM doing exactly what it was supposed to do and the truck would run/tow fine on 87 octane. I believe that what I stumbled onto by running 89 octane is that the PCM did not feel the need to intervene in a low RPM/ High load situation that may have been inducing knock.

The science behind this is the fact that towing creates the perfect storm for an engine that is already prone to detonation. While towing the engine is under a higher load at low RPM, where almost all detonation/pinging would normally occur. The knock sensor communicates this to the PCM and forces the engine to make changes, usually timing, to prevent the knock. This change in timing creates decreased power at that time and forces a downshift. Or another possibility is that the knock sensor communicates to the PCM and actually forces a downshift in effort to counteract knock, the PCM realizing that an increase in RPM would mitigate knock since an engine is much less prone to knock at mid to high RPM.

 

I would be curious if you took note of other factors on your return trip. Which way was the wind blowing? Driving a giant brick down the road, especially towing, the wind makes a world of difference. If the wind picks up here and I'm heading into it, my truck downshifts. What about temperature difference? Was it hotter one way then the other? Did one way have more uphill and the other way have more downhill?

 

I believe one of the tuners on this forum made a post regarding the relation between timing retard and fuel octane rating.

 

He did, and that is why and when I decided to test it out.

 

I hear you.
-I'm very aware of the affect that even a slight breeze has on the camper. There was no noticeable wind during our trip down on Thursday and no tail wind on the return trip Sunday. Elevation is very much the same, the entire trip is at sea level. I also pull this camper pretty regularly on different terrain, wind, no-wind, interstate...that's why this was so noticeable.
-Temps have been steady for the last 10-14 days here.
-No other time, ever, has the truck stayed in 5th gear with the TC locked for so long while towing. And to be able to accelerate in 4th was never possible, the truck would always require a downshift to 3rd to regain any lost speed.
-My entire return trip was spent thinking to myself about how/why the engine/tranny was behaving so differently. If I could have explained it away to some other reason then I would not have come here.

I already had a pretty good idea in my head about what was happening. I'm really looking for others with the exact same experience or tuner/engineers with an extensive knowledge of how the Tundra PCM reacts and if this scenario is plausible.

There is mention in 2 other threads on this forum about the Tundra PCM modifying timing in an effort to mitigate knock. There is other evidence spread throughout other forums about what the Tundra PCM is capable of. My train of thought was very logical, if the PCM and knock sensor communicate to mitigate knock then an increase in octane wouldn't require said mitigating factors. The mitigating factors being either reduced power due to modified timing, a forced downshift, or both. If the PCM doesn't need to mitigate knock this would equate to a more enjoyable towing experience with increased MPG.

I will also clear up that I don't believe the increase in octane had a direct correlation to increased MPG. I believe the immediate increase in MPG comes from the truck being able to maintain a lower RPM at cruising speed while towing.

 

not at all scientific, but the last two times towing the raffle jeep (mildly built xj on old steel/wood deck trailer) between western slope and denver, i've run e-free (maverick 87) and averaged between 10.5 and 10.9 ish mpg. i don't do 90mph but i'm not doing 50mph either.

not towing, with e-free, i'm often over 17 mpg.

don't have any across the divide towing with ethanol 87, but i'm lucky if i break 16mpg empty

i don't bother bumping octane as i don't have anything fancy like a supercharger and toyota designs their engines to run on the urine from camels