It's time to put a bottle of fuel injector cleaner in the gas tank when I fill up today, and I got to wondering about the directions:

"For best results, add entire bottle to nearly empty gas tank"

So in theory, if I fill up when my tank is half empty, do I need to add a bottle of this stuff for my next two fill ups?

What do you think? <img src="/images/graemlins/confused.gif" alt="" />

Say what? I always add it to a freshly FILLED tank.

I believe a nearly empty tank is suggested so that the act of filling it (after putting in the cleaner) stirs up the contents. Five miles of road travel would have the same effect.

It should mix up on it's lonesome just letting it sit long enough (time depends on temperature). But if your tank is completely full and you put it into the top of the fill pipe, it might take a while to get down to the tank. "For Best Results" being the key term. It just means with a nearly empty tank, you get faster mixing, and presumably a more spread-out concentration. But I can't imagine that half a gallon burned without the stuff makes that big a difference either way. I'd say "marketing" was involved in the language. <img src="/images/graemlins/smile.gif" alt="" />

I ran out of gas in a TR2 roadster. Oddly enough, I had possession ( illegal at my age of 17) of a bottle of EVERCLEAR grain alcohol. I was just far enough from the station to rule out pushing the beast and to proud to walk past my foes with a gascan. Into the tank and SUs went the everclear. The resulting backfire looked something like Sir Whittle's first flight of his jet engine. I think the SUs had to be rebuilt soon after. <img src="/images/graemlins/blush.gif" alt="" />

Marketing is ALWAYS involved I think. Almost every bottle of shampoo says "Lather, Rinse, Repeat"...how many people actually repeat? You'd use twice the amount of 'poo, and not much difference in the cleaness of your hair!

Another point I forgot to mention in the original post is I was wondering about diluting the concentration of the additive. I fill up the tank and put in the juice, which is designed to treat no more than 21 gallons of gas. Then my tank is half empty and I fill up again. So now the additive is diluted even further. Does it do what it's intended to do, or does it only work while the gas in going through the system that the additive originally treated, and the rest gets "watered" down to where it does no good?

Does that make sense?

I read the term "splash mix" once in regards to full strength antifreeze and water. I understand the reasoning about putting the stuff in and letting the new gas splash mix it, but I'm wondering more if I'm getting my money's worth out of the additive, or whether it is only working for the half a tank before I refill.

Ideas?

I'm quite sure it depends on the specific product. It probably has a dosing based on a certain number of gallons (small 15-25gal or larger 25-35gal). So, mix it in with a full tank, burn off as much of that tank as you can before refilling (so you get the full concentration) and then do it again at the next recommended interval. The weak concentration left over may do some good, but they are usually formulated to dispense their cleaning or lubricating powers in one tank.

STP Fuel Injector & Carburetor Cleaner: "Upon opening, pour entire contents in gas tank. One bottle treats up to 21 gallons."

Prestone Fuel Injector Cleanrer: "Add entire contents to tank of gasoline. One bottle treats up to 20 gallons."

If you have a 40-gal gas tank, add two.

Sue

The directions to add to a near empty tank has to do with it being mixed well with the fuel you put in immediately after the additive, dumping a full tankful on top mixes better than dropping the additive into a full tank... make sense???

Troy

Fuel injector cleaner works better if you pour it into a nearly empty tank because there is less gas to dilute the cleaner. It will do a quicker job of cleaning the injectors with a higher concentration of cleaner. If you are using gas treatment there is a lot of alcohol in it to remove any water in the tank. If you don't dilute the alcohol it can degrade compontents in your fuel system.

Of course if you are running with SU's the odds are that there was going to be an overhaul in the near future anyway.