I have an 11 year old truck and I know it does not require the higher octane gas. With that said, my truck does get better mileage and runs smoother on the higher octane. My question is, if I added the octane boost to regular gas give the same results or am I throwing money away?

 

I've never put a whole lot of faith in the "pour-in" octane boosters, and have heard a few horror stories. Mainly because you can easily add too much or not enough, and it's virtually impossible to know exactly how much gas is in the tank. Adding not enough will have no noticeable effect, and is just wasting money. Adding too much can be dangerous to the motor.

If you find that medium(89) or hi-test (93 or 94) makes it run better, then it's fine, and not hurting anything, though I've never noticed that putting premium in motors not designed for it gains any benefits. Otherwise, the manufacturer would just require premium from the factory if it ran better with it.

 

x2 on RaWarrior's comments, with one additional comment.

If you're running higher octane than necessary, there is some risk of carbon buildup. Octane is essentially a measure of resistance to ignition. If the motor is not designed for the higher octane and doesn't otherwise need it, there may be an increase in incompletely burned residue left behind.

On one hand, you may already have some combustion chamber deposits making the higher octane beneficial towards any pinging or knocking issues. You may wish to consider running some combustion chamber cleaner through.

On the other hand, I think the limits are being pushed to get gas out as cheaply as possibly while still striving to meet the various spec's. Another consideration is that 'winter' gas is coming out. This fuel is supposedly a slightly lower octane and who knows what all else, meant to help with cold weather starts and operation due to its higher volatility.

Unfortunately, higher volatility relates to lower mileage. Some people who track their gas mileage to the Nth degree will notice a slight drop in mileage in the fall, which picks back up in the spring when 'summer' gas comes out.

 

I really see the difference driving on the highway. Also I live up on a mountain and its about 2 miles diving up to the house and the motor seems to be smoother going up with the higher octane.

 

If it runs better and gets better mileage with high octane, use it if you want and can justify the higher cost. Don't try to do the same thing with additives, it's not the same.