I noticed that my gas cap recomends premium gas, but I cant afford to be filling up on premium every few days. So I went out and bought some Octane boost but is it worth the price. Also can it do any damage to my engine?

Those bottles of octane booster won't add a significant amount of octane - it really depends on which you buy (see here).

The difference per fill up of regular vs. premium fuel really isn't such a large difference in my opinion and is well worth it for the improved performance. I'd just buy higher octane fuel in the first place.

better to pay a little extra than risk your engine's life or performance

From the '01 owner's manual:

NISSAN does not recommend the use of any
fuel additives (i.e.: fuel injector cleaner, octane
booster, intake valve deposit removers, etc.)
which are sold commercially.

But the '01 PF has a knock sensor. Running regular gas probably won't hurt the motor,
but you'll get a bit better gas mileage on premium, which willl make up for the price
bump.


Chuclk

I was about to chime in and say 87/regular is fine, but looks like the '01 manual is pretty strict about only using 91/premium in the 3.5L. The 03 and 04 manuals say you can use regular or premium. Weird, since it's the same engine in both.

Does anyone know why they changed? Just curious; like how in 01 and 02 they OK the use of synthetic oil, and in 03 and 04 they say NOT to use synthetic.

I know this subject (regular vs. premium) has been discussed before, so I'm going to share my personal experiences and results in this area, as opposed to just posting an opinion or guess.
I have a 2002 Pathfiner with 255,000 kms, that I've had since almost new.
I've tried all different grades of fuel, and for the past five years, I've been running 87 octane regular fuel.
First of all, It has NOT ruined my engine, as some seem to think it should.
It still runs perfect, and uses no oil.
I've tried using mid grade and premium, and honestly saw no difference in performance. It runs just as good on regular as it does on premium.
As for gas mileage being that much better on premium so that I'll recover the cost difference....Absolutely NOT.
Gas mileage is the same, regardless of what I run.
With Canadian gas prices being what they are, I cannot see a single reason why I would switch back to premium.
Sorry to rain on the parade, but for me, the proof is in the pudding. Regular gas all the way.
Thanks.

I don't recall anybody claiming 87 octane would cause engine damage or other ill effects. My Pathfinder ran 87 for most of its life (about 110k out of its current 132k miles) and there have never been any fuel related issues. I feel a performance difference between 87 and 93 octane, so I will continue to run 91 or higher octane gasoline.

I decided to try out the octane boost and see no increase in performance but note that the octane boost I used is the cheapest brand I found at car quest.