Octane rating advice

Sorry for the somewhat silly question but it's something that has been bugging at me since I bought my truck. I'm pretty sure I know the answer but I have been going off my salesman's answer since I purchased it in April.

Here's my question.
In the city I live in there are only 2 Chevron gas stations and that's my fuel of choice. Problem is their octane ratings are as follows: Regular 86, Mid 88, and Premium 90. Price difference between the 3 are crazy, like almost a dollar per gallon. So... Is the 1 point difference really a huge factor? Should I be running the 88 rather than the 86 (salesman said the extra money for the 1 point wasn't worth it) since our manual recommends 87?

 

Define "worth it" for us. It's completely subjective. The manual recommends no less than 87 octane, and all a higher octane does is reduce the fuels tendency to knock (detonate early). Modern vehicles will run on just about anything, and the computer will adjust the timing and such to account for lower octanes, but running and running well are two different things. I'd suggest doing a bit of reading on why there are different octanes and what they do in order to find out if it is "worth it" for you.

 

Completely understand it's a subjective question. I am really just looking for thoughts and opinions on the topic that's about it. I could care less if it gave me better fuel mileage and I probably won't keep this truck for longer than 4-5 years, but if I could save from some costly repairs or maintenance down the road that might catch my ear

 

If the new trucks are anything like the old models, you won't likely see the results of lower quality fuel rearing up as a major issue in the first 5 years. It'll be something the second owner would be saddled with.

The octane question is pretty simple IMO. Pre-detonation is undesirable at best and damaging at worst. An extra 10 bucks per fill up to never worry about it is worth it for me to know that I'm never going to have any of the problems that it could cause. Like I said, modern vehicles will compensate for it and avoid most of the troubles, but it won't run as well. I'd rather have it run at it's best with minimal risk. I pay a stupid high price for zero ethanol 91+ octane, and my truck seems to love it.

 

Im guessing it would run fine on 86(ie not blow up) but it would probably have to reduce power, especially at lower rpm, to prevent predetonation. Basically limit boost to ensure cylinder pressures stay low enough.

The Ecoboost engines have a octane adjust ratio, which is basically a learned octane based on how much spark it can run over time. The oar can be anywhere from +1 to -1. Then there are 3 tables that limit air load corresponding to +1, 0, -1. If you were to run like 85 or 86 octane in the truck it would probably end up at a +0.5 oar and would blend two of the tables and limit power accordingly.

I def wouldn’t attempt to tow or do anything similarly strenuous on lower octane though.

 

^ This.

Alternatively find a different tier 1 fuel station that has 87 Octane if it is priced decently. If this were a naturally aspirated engine and you live at higher elevations the 85 or 86 Octane would be a non issue since the ambient air density is lower and cylinder pressures will be correspondingly lower. Since it is a turbocharged engine your altitude is likely not relevant since the turbos are probably able to make full manifold pressure where you live, and will need that 87 Octane to make rated power under load safely.

@mass-hole can comment a bit more on towing with a TTV6 since he's coming from an EcoBoost, but it might not be a bad idea if you are towing to spring for the 91 Octane fuel particularly in hot weather, just to hedge against detonation from hotter incoming charge air and reduced cooling capacity due to higher ambient temps. He also has some insightful observations of modifications to the EcoBoost Fords to increase the cooling capacity and improve thermal management of the truck to avoid issues on a hot day when working the truck hard.

 

This guy knows more about the tundra engine than the Toyota engineers. He has also done the tests to back up what he says.
https://daptuning.com/faqs

Do Ineed to run Premium Fuel?
As we have reported with every truck we have tested on, 4.6L, 4.7L, 5.7L, all run best on 91+ octane whether they are completely stock with stock tune, or tuned. These engines pull 8-12 degrees of timing due to knock retard on 87 oct, 6-10 deg on 89oct, 2-6 deg on 91oct, and 0-2deg on 93oct. That is on a completely stock truck with factory tune. If you care about the engine in your $35,000-$65,000 truck as you think you do, you wont run anything but premium in it weather you are tuned or not tuned.

And if you know engines, you know that retarding timing DOES cause accelerated wear.

So i run the highest octane i can find at the pump, which for me is typically 91.

Yes, your engine can run for many many miles without issue on 87. And if you are really struggling with gas prices, then run the cheapest gas you can find and don't worry about it. But if you do have the money, i would recommend running 91-93 octane because it is legitimately better for your engine.

This advice is specific to the Toyota tundra and NO other vehicle. So don't come at me about how your 1996 civic went 400k miles on 87 octane.

 

Doubt anyone knows better than Toyota themselves. If they say 87 then 87 I’m sure is perfectly fine. They wouldn’t recommend an octane that’s going to decrease engine life or cause excessive issues. It would have been simple to recommend higher octane if they believed that’s what was best.

 

Interesting that this question was asked, as I was just about to ask a similar question.

We just had a Sheetz gas station open right down the road from my house, and they offer 90 octane "pure gas" zero ethanol. It's only 20 cents more than 87 octane with 10% ethanol. Would I see any benefit or performance/fuel economy increase by using this fuel?

 

They would, and they do.

It isn't that simple to recommend higher octane. The Tundra already is one of the lowest selling full size trucks on the market, how many fewer do you think they would sell if they slapped a "requires 91 or higher octane" sticker on it?

And as I pointed out previously, Toyota doesn't care if your engine lasts 300k miles. All they care about is that it lasts through the warranty period.

and as with ANY mechanical contraption, there are trade-offs in the design. The engineers make a big list of specifications and as long as the engine can meet those minimum specifications, they go with it. Even if making a slightly more expensive change would make the engine twice as good in that specific aspect.

And so, when Toyota designed the engine, they decided that the ECU retarding spark timing to 10-15 degrees would fall within their acceptable specifications, knowing full well that would decrease longevity and increase maintenance costs. But it didn't matter because those issues would not show up until Toyota was no longer responsible for the repairs.

So go ahead and run 87 if you want. And sure, your engine might run for 250k or even 450k miles. But don't make the mistake of assuming that you are going to get the absolute best performance and life out of your engine by running the minimum recommended octane.

 

I’ve seen it theorized that the 87 octane spec could be more of a marketing decision rather than a engineering one.

If consumers are comparing trucks that are similar in price, capability, etc. and one advertises that it runs on 87 octane and the other requires 93, people may be driven towards the lower octane truck since that has a lower cost of ownership. It’s like comparing two trucks with similar specs but one gets 20MPG and the other 16MPG.

So it’s possible the truck makes full power on higher octane, but will run just fine on regular gas too if that’s what you decide to put in it.

 

Depends on the situation but there’s some potential. Toyota uses a torque request style of control so the engine won’t make any extra torque because of how it’s tuned no matter what octane you run. But if you’re getting spark timing pulled due to hot air temps or anything else, you can recover the spark timing with better octane. Higher octane lets the engine use the maximum brake torque spark timing which can yield very slightly better fuel economy.

 

My truck has 120,000 miles on it. Has run regular fuel the entire lifespan.

Using fuel prices today, it has consumed about $31,000 ($3.65/gal) in fuel. Had I used premium ($5.21/gal) it would’ve consumed $44,000 in fuel. Over 200,000 miles you are looking at over $20,000 difference in regular fuel vs premium ($52,000 vs $74,000).

The truck was only $33k new. I’ll keep using regular.

 

If you have 86 and 88 available, you could make your own 87 mix, if you are interested in the lowest cost to meet the minimum recommendation.

 

The 87 octane requirement is at sea level. At your elevation, 86 is equivalent to 87 at sea level. You have less oxygen, the flame path in the combustion chamber is slower than it would be at sea level, thus there would be no predetonation under normal circumstances. You don't need the 87 at high elevations, like in most of NM, CO, WY, etc. Your power output will be lower, not because of detuning by the ECU to prevent predetonation, but because you don't have the oxygen at that elevation to support the power output at sea level. Don't sweat it.

However, just now noticing that you have a '22 model, turbocharged, you'll likely run into some timing pulldown to prevent knocking while in boost. When I lived in Albuquerque, I had a turbocharged Volvo. 86 octane won't hurt your engine, but it will run better (i.e. stronger) with higher octane. If you drive reasonably, and stay out of the turbo, the octane difference won't matter. Then again, I'm not sure how easy it is to stay out of the turbo on a 6 cylinder engine pulling a 6000 pound truck. Still, the 86 will not hurt your engine. The ECU will see to that.

 

lol nice slight of hand there. You use todays ridiculous gas prices and apply them to the life of your truck, and then compare that over-blown number to the low purchase price of your truck.

Remember, just 2 years ago, gas was HALF the price it is now. And right NOW, the price of a new Tundra is above $50k.

And sure, I guess if you like buying a new truck every 3-5 years, it doesn't matter what octane you run. You aren't the one that has to deal with the repairs down the road. But for those of us looking to get every last mile out of our trucks, then 91+ octane is the way to go.

Because paying an extra $1.2k a year in gas is still much less money out of my pocket than buying a new truck every 5 or even 10 years.

 

It’s odd that it bothers you so much that someone may use other than 91 in their truck. I’m not denying that it’s mechanically superior. I’m saying your fear mongering over use of regular fuel is unnecessary and completely downplays the added costs of premium fuel.

I bet you love a good extended warranty. It’s only a little more each month!

 

That’s not how turbocharged engines work. They generally produce the same absolute manifold pressure despite outside pressure. So if 70 mph cruising at 1500 rpm requires 5 psi of boost, at 7000 ft the turbo will produce 8.5 psi to compensate for the 3.5 psi drop in pressure. The boost doesn’t really run out until very high rpms (both engine and turbo rpms).

 

The highest octane we can get here is 94 but I'm pretty sure it's just 91 (which had no ethanol) that's been dosed with enough ethanol to boost the octane. Does he say anything about the ethanol content of the fuel he tested?

 

Probably a small fuel economy boost as ethanol has less energy density. Run a tank of each in similar driving conditions and hand calculate the fuel economy for each one to see if it's worth it but my guess is that it is. That's a pretty small price difference.

 

It doesn't bother me and I'm not fear mongering. I've said several times now to run whatever you want. The ONLY thing I am doing is pointing out the fact that higher octane is better.

And no, I don't buy the extended warranties. But I do take care of my stuff. And wouldn't you know it? All my stuff lasts a long time. Weird.

 

I towed for a while using 87/88 here in Utah and the truck did ok. I never noticed anything bad. However, in the last 5 years the price of 87/88 and 91 has compressed to only being 10-15 cents more per gallon. So at some point I just started running 91 every single tank because the cost difference was minimal.

Now, when I tow, I dump Boostane into the tank as well and run 94 octane. Boostane only costs 15 cents per gallon of fuel for the 3 octane points, so its not that expensive. Especially at higher loads, the engine can absolutely take advantage of the extra octane. These engines can realistically take advantage of E50 or E85 if you let them.

The thing is, when you are towing, using the higher octane allows the engine to operate at lower boost because its making the required power with spark vs just trying to cram more air in. The reduces heat from the turbos, and just lets the engine operate in a happier mode. It also makes the engine a lot more consistent.

The engine can operate totally fine on 87. Its not grandpas port injected 1994 Camaro. The direct injection, turbos and super fine control they have over spark makes them extremely tolerant to octane. I bet the truck could run on 85 octane just fine, although I wouldnt recommend it.

All they have to do is reduce the amount of boost to be able to run lower octane. It won't make the advertised power or drive as well, but it will run. It would be like saying an NA 3.5L with a 10.5:1 compression ratio can't run 87. We all know they can. GM's 5.3L V8 runs 87 with an 11:1 compression ratio.

To get to MBT in these engines at WOT you likely need over 100 octane. The Ecoboosts are able to utilize E85 to get to MBT and they run the same compression ratio.

So yeah, any additional octane you feed them will likely improve power and efficieny to some degree, but there will be a limit. Eventually they won't allow the engine to run additional spark because it will eventually create more torque than they want it too for a given air load.

They likely designed the engine to operate at MBT at light load like you would see in the EPA MPG testing. Anything above that average state probably loses MBT spark on normal octanes. By running a lower or higher octane you are just moving at what load MBT occurs. My F150 Ecoboost can run MBT at steady state 55 mph driving but once I start climbing hills, driving faster, or towing, it can no longer hold MBT without insane amounts of octane. Even on 94 its not MBT under anything much more than steady state cruising.

I don't think these engines(GTDI's in general) dislike ethanol the same way a NA V8 might. The added cooling effect of the ethanol in the cylinder I think may help things even though the octane might be the same.

 

I recommend running aviation fuel.

 

Dang this thread blew up overnight!
Thanks for all your responses, I think it is just good information to have when you have a bunch of knowledgeable people giving their thoughts and opinions. Cost isn't a problem, I will likely start using the higher octane fuel from here on out. Not necessarily for me (as I only tow and work the truck hard a few times a year) but more for the peace of mind and benefit for the person who buys my truck from me in 4 or 5 years.

With that here is another question! It would be safe to say, there is nothing wrong with running the 88 octane from here on out and switching to the higher 90 or 91 when I know a camping trip or towing event is coming up right?

 

What exactly is the price difference? At almost $1 difference per gallon it won’t pay off in the long run to use the higher grade.

 

I wonder if tundras who made million miles used premium fuel?
@Medic343 , how is 5+4+3=2?

 

I was going to ask the same thing. I was trying not to distract this thread from the 3rd Gen but it looks like we're already there.

 

Thats exactly what I would do. Run the cheaper fuel for daily driving and when you tow run higher octane.

 

You won't notice anything bad. It is a long, slow, process. Like drinking coke or smoking. You can do it for years, feeling absolutely fine the entire time, until you wake up one day not feeling quite right, then a few months later your doctor tells you that you have diabetes or lung cancer.

What the lower octane fuel does is cause the ECU to retard spark timing. Meaning the spark is not igniting the air/fuel mixture at the optimal time, meaning not all of the fuel is being burned. This causes carbon deposits to slowly build up in the combustion chamber and exhaust manifolds. The carbon build up eventually builds up enough to cause scoring on the cylinder walls, piston rings, and exhaust valves and valve seats. And again, this is a long, slow, process. Your engine will likely run for a couple hundred thousand miles before you notice anything bad, and by then you'll chalk the problem up to age or normal wear and tear.

 

That's not really how it works.

It is the daily driving that does the damage. Your engine works the hardest and gains the most wear while driving in city traffic. Rush hour, stop and go, red lights, drive through lanes, etc.. Every mile driven in the city is worth 100 miles driven on the highway.

Also, your ECU can't just switch from running 87 to 91 immediately. It takes 3-5 full tanks of gas before your ECU adjusts the timing and other specs to most efficiently run higher octane gas.

If you really want to swap back and forth, I would run the low octane gas for 20 tanks, then run high octane for 5 tanks. That will prevent the low octane gas from building up too much carbon, and allow the high octane gas (that also usually has more detergents) to clean out some of what does build up.

It still isn't ideal, but it is definitely better than just running 87 all the time.