I went on a fairly long trip this morning to a meeting and back (~100 miles each way). I stopped by the gas station on the way home to fill 'er back up. I was pumping gas, and the pump cut off what seemed like WAY too early. So I tried it again (even though you're not supposed to "top off"). It gets about another gallon in there, and cuts off again. I still don't think it's full, but I decide not to push it because I was thinking about how extremely conservative the gas gauge is (as we all know). So I get in the car, and the gauge only goes up to about 2/3 full. What gives?

My only guess is that that the pressure in the fuel tank (which is what causes the pump to cut off) might have been artificially high due to my trip (I was doing about 80/3500RPM almost the whole way). I haven't gassed up again since, so I don't know for sure. Any ideas? Anyone else had this happen with their TSX or other car?

 

I have typically found this has more to do with the pump and not the car. Try your next fillup at another station and pump and my guess is you will not have this problem again.

Just my

 

I agree. Probably the pump.

 

My guess would be the pump as well, I've had it happen with my old car a couple times.

 

What is the harm in "topping off"? Is it bad for the car, for the environment or what?

 

The same thing happened to me, except my car was actually full. I got a nice stream of gas running out of the little hole under the filler. It exits the car RIGHT near the hot exhaust.

 

From what I've read, here are some reasons not to top off your car (note: some of them may be inaccurate; i'm only repeating what I've heard/read)

1) You could completely fill the tank, causing excess gas to splash all over the car and possibly onto yourself.

2) If the pressure in your fuel tank increases (for example, due to heat), then your fuel system will automatically vent some fumes. If your car's tank is completely filled when this happens, your car will leak gas instead of air (which is dangerous as well as a waste).

3) It can screw up the pump for the person that uses it after you. I can't remember exactly what it does (maybe it cuts off too early?)

4) Topping off releases more fumes (including benzene, a carcinogen) into the air, which affects your health and increases pollution.

5) On some systems, if you try to top off, the extra gas will go back into the nozzle, yet you will be charged for it anyway.

 

It is supposed to be bad for the environment... a contributor to smog. I personally think it is a bunch of crap.

 

Gas is subject to volume changes due to temparature. If you top off in extremely cold weather at your corner gas station the "cold" gas will have a certain volume. When you park in your heated garage the gas will expand in volume and spill out from the opening.

This happened with my '93 Civic DX. I filled up with gas on a cold canadian winter morning several blocks from my indoor parking lot at the office. Once in the lot the gas heated up, expanded and spilled all over the floor. The 7 story building filled up with the smell of gas and someone, to my embarrassment, called the fire dept.

Don't top up.

 

I have had that problem, but it would cut-off every pint or so even though the tank is far from full.

According a gas station person, it's caused by these dolts who insist on topping-off their full tanks. Air or pressure or someting gets into the pump's fuel line, and that screws up things for customers who pump after the dolts.

There's a reason why gas station tanks often include signs, "Do not top off."