CarTalk.com Blogs Car Info Our Show Deals Mechanics Files Vehicle Donation

How much gas to fill up with?

When at the pump, should I stop filling when the pump automatically stops, or should I put extra gas in? I basically want to know if the emissions system on my 2006 car will evaporate the gas if extra is added or if it will be usable?

Thank you for your time.

Always stop when the pump stops. Putting more in can force gas into the evaporative control system, and can damage it.

Stop when the pump stops. It stops for a reason.

It depends. On my Mustang when the pump clicks off the first time, the tank is about 97% full, you can get about another 1/4 gallon in and that’s it, after that it starts pooling at the top of the filler neck. On F-150 it’s quite a bit different, when the pump clicks off, the first time you can still get another 3 or 4 gallons in easily, it’s been like that since I’ve owned the truck. On my TR6, the filler neck is vertical and it lacks any type of evap system, when the pump clicks off , it’s totally full.

Curiously when I had my Bronco, it too wasn’t quite full when the pump clicked off the first time. I could get another 3 gallons into it after the first automatic stop.

With that said, it’s a good policy to simply stop pumping after the first click off.

If that is my car, don’t put gas in there, I have a diesel.

Yea, don’t try to top it off. It is very possible that you could do some damage, even if it is not a sure thing. On the other hand, you have nothing to gain by stopping when you should.

JEM, I think you meant this: "On the other hand, you have nothing to gain lose by stopping when you should. "

It varies with the car. On my old Dodge I can fill it up until the fuel level is visible at the top of the filler neck. Never had a problem in 18 years.

Many recent cars will strongly object to this method. I don’t know why they can’t build 'em to prevent such problems, but that’s what’s out there. If you’re not sure, quit early.

FoDaddy, you’re certainly free to top off all your tanks if you want, but understand that you do so at your own risk. In addition to possible damage to the EVAP system, upir gas needs room to expand. It expands as the car sits in the sun, and it expands as you drive (agitated fluids take up more room than still fluids). Besides which, you just may want to park on an incline.

I recommend against it. I’ll fight for your right to do it, but I recommend against it.

When on a long trip or when encountering a low gas price, I have packed the gas tank on various GM cars over the years and have never had a problem. Some brands might not like it, however. Be careful to not do this on a day when the outdoor temperature is rising and you must park the car immediately after filling.

I stop at the first click. I really had to bite my tongue when the girl next to me kept clicking and clicking and clicking it. Maybe I should have said something but then she probably would have told me to mind my own business. She was too young to be a carryover from watching her dad do it on non emissions controled cars back in the 50’s. I did the next best thing and told my wife who just kind of looked at me like I was over-reacting again.

Yes stop stop stop. What difference does it make?

I always stop at the first click. This way I get better gasoline mileage because pumping in the extra fuel adds weight. I set up a differential equation and estimated that by stopping at the first click of the pump rather than to fill the tank to the brim that I gain .000001 mpg. Every little bit helps.

Quote from Triedaq: “I set up a differential equation and estimated that by stopping at the first click of the pump rather than to fill the tank to the brim that I gain .000001 mpg.” unquote

If you can put more gas into your tank then you don’t burn gas as often going to the gas station to fill again. Did your equation incorporate that too? If not, cancel that .000001 mpg gain.

The question of whether or not to keep forcing more gas into your tank after the pump clicks off for the first time probably comes down the issue of where you will be driving that vehicle. If I was about to drive across the trackless wastes of the Atacama Desert, I would probably try to force as much gas into the tank as was possible, simply because it would be–literally–a survival issue.

On the other hand, if I was driving in the more settled areas of the lower 48 states, I would err on the side of caution and do exactly what most Owner’s Manuals state regarding this issue, namely…Do not continue to fill the tank after the gas pump clicks off for the first time.

Why do I say that? Because I have observed the outcome of doing the click-click-click routine with the gas nozzle.

I repeatedly warned a friend of mine about this practice, but he ignored me. A couple of months later, when he began to have problems fueling his Toyota Highlander (circa 1999), it turned out that the carbon canister in his Evaporative Emissions System had been saturated with liquid gasoline, rather than the gasoline vapor that it was designed to deal with.

The bottom line is that he wound up paying over $300 for replacement of that carbon canister, which was a totally avoidable expense if he had just followed the advice provided by both his Owner’s Manual and by me. In case you were wondering, he never has the occasion to drive more than…perhaps…10 miles from a gas station.

Yup!
Repair costs that were totally avoidable…and that were the result of totally foolish behavior.

"I always stop at the first click. This way I get better gasoline mileage because pumping in the extra fuel adds weight. I set up a differential equation and estimated that by stopping at the first click of the pump rather than to fill the tank to the brim that I gain .000001 mpg. Every little bit helps. "

I sincerely hope that’s a joke. Doing the math I find that this saves you 0.06 inches per gallon (assuming, of course, that your method does anything at all). Assuming 20 gallons of gasoline per fuel stop you’d save about an inch and a quarter per tankful. Over the entire lifetime of the car there isn’t enough of a saving to drive from the street to a fuel pump at a gas station.

@JayWB–“I sincerely hope that’s a joke”. I was being sarcastic. I don’t think it makes a bit of sense to continue beyond the first click. When I fill up, I put the nozzle in the tank and, as the tank is filling up, wash the windshield. I watch to make certain that the nozzle doesn’t pop out of the tank. When it clicks off, I remove the nozzle, hang it up on the pump and then often raise the hood and check the oil.
Unless service stations are few and far between, I see absolutely no reason not to stop filling when the nozzle first clicks off.

FIRST CLICK!!!

Mopars don’t seem to care if you top them off in my experience, but my newest car is 7 years old. Fill it till it clicks and squeeze a few cents more if you want to make the total neat, but don’t cram as much gas as you can possibly fit in your car.

TSM, I know about the evap system and the charcoal canisters and such. But the truth, it’s I’ve never had an issue with it, and this included topping off my Bronco for over 200k miles. Theoretically, I should’ve had to replace a canister or two by now, but there have been no check engine lights, no evap OBD II codes, no anything. Maybe I’m just living a charmed life.

+1 with all the comments to stop filling when the pump stops.

Why add the extra gas anyway?
What’s the advantage?
Will it allow you to cruise that much further?
Why even ask the question?

RemcoW, with my Mustang, I just pump enough in after the automatic stop, to get to the next even dollar amount, it makes record keeping a bit easier, and at $4 a gallon or whatever at most we’re talking 1/4 gallon so extra. Nothing to worry over. For the F-150 for some reason it trips the automatic cutoff well before it’s full, usually 3 or 4 gallons before it’s full. So I just manually feed more (at about 1/4 of the full flow rate) in until the automatic shutoff happens again. It’s always done this, I’m not sure why though.