# Topping off the gas tank... good or bad? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [October 10, 2008, 6:51pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584 "2008-10-10T18:51:10Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![criscris](https://avatars.discourse-cdn.com/v4/letter/c/35a633/32.png) [@criscris](https://community.cartalk.com/u/criscris)\ **Post date:** [October 10, 2008, 6:51pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/1 "2008-10-10T18:51:10Z")
The other day I was at my local gas pump and a friend of mine noticed I topped off my tank. He said I shouldn’t do that because of some gunk build up in the hose that will get into my vehicle and ruin something-or-other in my car ( maybe my catalytic converter). I’m driving a 2002 Honda CRV if that makes a difference. I have always topped it off so that I have the same amount of gas each time to accurately compare my mileage. To top or not to top, that is my question. ---
**Author:** ![jayhawkroy](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/jayhawkroy/32/33_2.png) [@jayhawkroy](https://community.cartalk.com/u/jayhawkroy)\ **Post date:** [October 10, 2008, 6:55pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/2 "2008-10-10T18:55:56Z")
Don’t top it off. Excessive topping off can lead to charcoal canister failure, which is expensive to replace. Top to one click so long as the nozzle fills you full and doesn’t shut off prematurely. ---
**Author:** ![Docnick](https://avatars.discourse-cdn.com/v4/letter/d/ecae2f/32.png) [@Docnick](https://community.cartalk.com/u/Docnick)\ **Post date:** [October 10, 2008, 7:09pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/3 "2008-10-10T19:09:05Z")
We’ve had several posts on this; on a modern car, topping off the tank is really bad; it screws up the evaporative control system and may lead to expensive repairs, such as the charcoal canister replacement. Most instruction manuals tell you NOT to top off the tank. If you tank at the same pump, and stop at the first click, you can get an accurate figure of you gas mileage. ---
**Author:** ![hoffmalr](https://avatars.discourse-cdn.com/v4/letter/h/bc8723/32.png) [@hoffmalr](https://community.cartalk.com/u/hoffmalr)\ **Post date:** [October 10, 2008, 7:20pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/4 "2008-10-10T19:20:01Z")
Your friend has a silly reason, but he’s right. Don’t top it off. Jayhawkroy and Docnick told you why - it’s bad for the evaporative system and will cost you a bundle to have it fixed. As for mileage, a small difference in the amount of fuel in your tank won’t make any difference at all averaged over a few fillups. ---
**Author:** ![the\_same\_mountainbike](https://avatars.discourse-cdn.com/v4/letter/t/c89c15/32.png) [@the\_same\_mountainbike](https://community.cartalk.com/u/the_same_mountainbike)\ **Post date:** [October 10, 2008, 8:47pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/5 "2008-10-10T20:47:54Z")
They’re all correct. Topping off the tank creates the risk of saturating the charcoal bed in the charcoal canister, part of your evaporative emissions system. Do that and you’ll be out hundreds of dollars. ---
**Author:** ![Wha-Who](https://avatars.discourse-cdn.com/v4/letter/w/9f8e36/32.png) [@Wha-Who](https://community.cartalk.com/u/Wha-Who)\ **Post date:** [October 10, 2008, 9:15pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/6 "2008-10-10T21:15:35Z")
Possibly some brands are more tolerant of this than others. I have repeatedly topped off the tank on a 90s Chevrolet Cavalier and three recent Chevrolet Malibus from 1999 to 2005 with no apparent problem; no check engine light. Our newest GM car, a 2008, will not permit topping. When the filler nozzle clicks off, no more gas will go in. ---
**Author:** ![tardis](https://avatars.discourse-cdn.com/v4/letter/t/f0a364/32.png) [@tardis](https://community.cartalk.com/u/tardis)\ **Post date:** [October 10, 2008, 9:36pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/7 "2008-10-10T21:36:55Z")
Yes, my two Lincoln LS’s have never had a problem and we top them all the time. The same was true of the Grand Marquis’ we had before. ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [October 10, 2008, 11:42pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/8 "2008-10-10T23:42:18Z")
That is true. Some cars don’t share this problem. You can identify them because the owner’s manual does not say anything about it and there are no stickers on the car (usually in the glove box or under the cap covering the filler) warning you not to do it. Personally I recommend not topping off the tank on any car so you don’t get in the habit and then overfill someone else’s tank. After all what do you gain. It does not get any cheaper when you add more. ---
**Author:** ![lenjack](https://avatars.discourse-cdn.com/v4/letter/l/f475e1/32.png) [@lenjack](https://community.cartalk.com/u/lenjack)\ **Post date:** [October 11, 2008, 2:31am UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/9 "2008-10-11T02:31:05Z")
Cannister repair about $400. Not worth getting that very last drop! ---
**Author:** ![pleasedodgevan](https://avatars.discourse-cdn.com/v4/letter/p/51bf81/32.png) [@pleasedodgevan](https://community.cartalk.com/u/pleasedodgevan)\ **Post date:** [October 11, 2008, 4:19am UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/10 "2008-10-11T04:19:41Z")
Don’t top off. Get the average mileage from your last five fillups if you are fussy. ---
**Author:** ![thecarguy](https://avatars.discourse-cdn.com/v4/letter/t/ea5d25/32.png) [@thecarguy](https://community.cartalk.com/u/thecarguy)\ **Post date:** [October 11, 2008, 9:52am UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/11 "2008-10-11T09:52:49Z")
ive never had any trouble topping mine off. ---
**Author:** ![Joseph\_E\_Meehan](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/joseph_e_meehan/32/21_2.png) [@Joseph\_E\_Meehan](https://community.cartalk.com/u/Joseph_E_Meehan)\ **Post date:** [October 11, 2008, 10:08am UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/12 "2008-10-11T10:08:06Z")
Some cars don’t have the problem. Older car’s don’t have the problem and it will not cause a problem every time, but I would suggest you are likely to have a problem with your next car if you continue with it. It’s your choice, but consider that you apparently value having that extra fuel in there and if you damage it you can’t get even the normal fuel in there. ---
**Author:** ![B.L.E](https://avatars.discourse-cdn.com/v4/letter/b/848f3c/32.png) [@B.L.E](https://community.cartalk.com/u/B.L.E)\ **Post date:** [October 11, 2008, 4:03pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/13 "2008-10-11T16:03:41Z")
Even in older cars without vapor recovery systems, filling all the way to the top can cause your tank to run over when you park your car out under the hot sun. Liquid gasoline expands a lot when it gets warm. ---
**Author:** ![ken\_green](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/ken_green/32/816_2.png) [@ken\_green](https://community.cartalk.com/u/ken_green)\ **Post date:** [October 11, 2008, 4:25pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/14 "2008-10-11T16:25:16Z")
See “p1443 p0174 ford thunderbird” posted today. Problems will arise when top filled into the neck. ---
**Author:** ![criscris](https://avatars.discourse-cdn.com/v4/letter/c/35a633/32.png) [@criscris](https://community.cartalk.com/u/criscris)\ **Post date:** [October 11, 2008, 11:52pm UTC](https://community.cartalk.com/t/topping-off-the-gas-tank-good-or-bad/20584/15 "2008-10-11T23:52:10Z")
Wow, thanks everyone! What a great resource. I’ll be a one click gal forever more because of you.