What grade fuel do you pump?

Your dad was/is wrong. It's simple chemistry. Think of it this way. When you mix your Jack and Coke does all the Jack magically turn into Coke???

Think before you type.

 

Same here, had the truck for about 6 weeks now. I have been using 87 and after this thread yesterday I filled up with mid grade. I can't really tell any difference in power from just normal driving. I go back to 87 next tank.

 

Was. or I would have checked.
As I said, it makes sense.
I do not sully my Jack.
Perhaps a splash of water; but coke; never!

 

A lot of stations do that. They have 2 tanks, 1 low, 1 high. Pumps draw from both to create mid. At least the ones I worked at did that. Cut down on the amount needed to be delivered. Some even offered high at low price when they ran out of low (because you couldn't pump low or mid).

 

I think I figured out those that do not notice the advantage to 91 plus
This is with just turning 300 miles... the dealer musta had 87 in it. I noticed some pinging (per say) while punching it. Those that drive normal will never notice the difference.. with 87 pickup is still good, just when you floor it... mine at least pings
Filled up tonight with 93 from bp... the ping is gone and the punch is all that much smoother...
Can't wait till the motors broke in so I can really whale on it

 

SO, what I understand so far is that if u use 87 you'll get more milleage but less power, and if u use 91 you'll get more power but less milleage??

Is that right??

 

No, you should get better mileage and power with higher octane fuel. But there's a catch - when you have more power you tend to abuse it, therefore reducing mileage. If you drive the same with either 87 or 91 you should get better mileage with the 91.

 

So, can somebody explain how higher octane gas gives more power when there's more energy in lower octane gas?

 

It's probably due to VVTI. I haven't found a good explanation of what exactly VVTI does though.

My guess, is your not getting extra power per say, but rather designed power. As in, the engine is designed to run on 91, but the VVTI adjust valve timing (retards it if I understand correctly) to allow you to run lower octanes without pinging. So you don't get extra mpg, power, etc. You're getting what the engineers designed it to get, and when running lower octane you just get less than it was designed to get (less than optimal performance). This going by the fact my manual says something like "for optimal performance use 91 octane gas", and my Corolla (pre-VVTI) states to use 87 octane. The Corolla manual also states it won't benefit from higher octane gas IIRC.

 

Think of it like older carburetted cars. I've never had one, but seems like you had to put a specific octane in them. If it pinged, you simply ran a higher octane (or adjusted the carb I guess). So you had to keep using the same octane, or keep adjusting the carb. If it ran on 87, the engine couldn't take advantage of higher octane and could detonate too early. Now, the VVTI does those adjustments automatically as needed so you can run just about anything without damaging the engine or tweaking things yourself.

I'm no motor head though so this is all just a guess from what I've read or heard people say. Makes sense to me though!

 

I found this article interesting.

6.16 What happens if I use the wrong octane fuel?

If you use a fuel with an octane rating below the requirement of the engine,
the management system may move the engine settings into an area of less
efficient combustion, resulting in reduced power and reduced fuel economy.
You will be losing both money and driveability. If you use a fuel with an
octane rating higher than what the engine can use, you are just wasting
money by paying for octane that you can not utilise. The additive packages
are matched to the engines using the fuel, for example intake valve deposit
control additive concentrations may be increased in the premium octane grade.
If your vehicle does not have a knock sensor, then using a fuel with an
octane rating significantly below the octane requirement of the engine means
that the little men with hammers will gleefully pummel your engine to pieces.

You should initially be guided by the vehicle manufacturer's recommendations,
however you can experiment, as the variations in vehicle tolerances can
mean that Octane Number Requirement for a given vehicle model can range
over 6 Octane Numbers. Caution should be used, and remember to compensate
if the conditions change, such as carrying more people or driving in
different ambient conditions. You can often reduce the octane of the fuel
you use in winter because the temperature decrease and possible humidity
changes may significantly reduce the octane requirement of the engine.

Use the octane that provides cost-effective driveability and performance,
using anything more is waste of money, and anything less could result in
an unscheduled, expensive visit to your mechanic.

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

 

It makes sense sometimes the benefits of a higher octane are just all in your head, since i got my truck i have only used mdgrade, i will see if regular works fine thanks for the info

 

I don't mean to be difficult, but none of this is really convincing to me. I'm sure part of that is my limited understanding of engines.

I decided to go find more info at wikipedia and I think that helps. It still leaves me unconvinced that going higher octane than regular (with my driving habits) would make a difference. One of the points in that article, is that unless you are pushing the limits of the engine's performance (high RPMs) the advantage of higher octane is reduced. Since I try to keep my RPMs under 2K for gas mileage purposes, higher octane still doesn't seem to make sense. But now I can see how more power is possible in higher octane, you just have to be pushing your engine to get it. Higher octane for better fuel economy still isn't clear to me though.

Also, oddly enough, on my last tank I decided to give myself a break from the 2K goal for fuel economy. I still wasn't crazy flooring it from every stop light or anything, but I drove it harder than usual. I went to fill up the other day and my MPG was the highest I've seen on the truck yet: 19.25 in 100% city driving. I'm going to see if this is repeatable.

 

I am confused now!!!

What should I use then??????????????

 

I'm happy to share

 

I think what he was trying to say in the article is that if your engine was designed to use higher octane (i.e. you get the best mileage and performance), but decide to use lower octane, your engine will automatically adjust itself to operate a little below its optimal settings. Therefore you would get less mileage and performance would decrease.

As for the new Tacoma's, when a lower octane fuel is used, the engine automatically retards the timing to prevent knocking. To me that is saying that the engine is actually designed to use a higher octane fuel, and that is why I use 91.

 

Yeah, there was that part, but also the part that the higher octane matters the most at higher RPMs. So, running higher octane with lower RPMs means you're not really getting the most out of the fuel, so mileage and performance also decrease in that scenario. I don't know which decrease is bigger and haven't heard a discussion about that.

Then to throw more variables into the ring, elevation and weather matters too.

I have some interest in all this in the abstract, but more practically, I want to know about it for my engine. My 07 owners manual says 87 octane. The only reason to question that is because I've heard the 05 owners manual (same engine) said a higher octane. I've heard others say the compression ratio on the engine straddles the fence between a rule of thumb for which octane to run. It just all seems so iffy here. Part of me just wants to trust the Toyota engineers who changed their mind on what to recommend for this engine. I can't see them having any advantage in recommending a lower octane than what is optimal for the engine.

 

The 06 manual says 91 too. So maybe they tweaked the engine settings and changed the manual in 07+.... Maybe they changed some ECU settings after seeing gas prices shoot up again or people complained about it "requiring" 91...