Is it better to fill up at the half way mark or to wait until empty?

[anon9]

Pretty simple. Should you fill up once you hit half a tank and bring yourself back up to full or just wait till empty?

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.

I want to know if there's any truth to that.

I had a Honda Accord for about 2 years and did that with no problems, but I just bought an 05 neon and I don't want to risk any long term problems.

[theclencher]

What gunk? :confused:

[hybriDatsun350]

The only time that it would be beneficial to wait until empty is when you are figuring your gas mileage manually. Burning the whole tank would give you a more accurate estimate of your mileage.

[R.I.D.E.]

half full when prices are rising, empty when they are falling, if that ever happens!

regards
gary

[JanGeo]

Actually to be more accurate - you want to fill it when prices are rising since you are buying it at the lowest price before it goes up and then you want to put more in sooner or until the price levels off then run it down to empty until the prices start to drop and then put in as little as needed to make it to the next price drop/day.

I get hit once a month so last week - 8 days ago - I paid 3.219 and now it is 3.509 or more. The 18 month price graph shows a peak then decrease around the 25th of May so we have another 30 cents to go before the peak - looks like $4 a gallon!

[swng]

I am not for waiting until the tank is almost empty to refill. Yet, IMHO, refilling too often may mean carrying a full tank too often and hence a heavier average load for the car over the time.

[kamesama980]

I fill any time under 1/2 to prevent what the driver almost did on a big trip last week....NOT fill up at 1/4 tank and the next 2 service stations were closed. luckily there was another guy stopped filling his gas tank with some cans and had some diesel cans too. DONT want to run the diesel empty. granted this was (very) limited access highway in the middle of nowhere northern PA

[Robin Hood]

Well, being in the tech field a bit, I don't know about saving gas and all, but bringing the fuel too low will wear out the fuel pump faster. Most pumps actually use the fuel in the tank to keep the pump cool and lubricated. Just thought I'd throw that in there for you guys.

[ihatemybike]

While it is true that a lot of fuel pumps use the engines fuel to keep them cool, most current fuel pump assemblies are designed to keep it submerged in a small cup even when the fuel level in the tank is much lower than the height of the pump. Knowledge gained from I've been replacing these in my vans recently.

[civic lover]

Well, being in the tech field a bit, I don't know about saving gas and all, but bringing the fuel too low will wear out the fuel pump faster. Most pumps actually use the fuel in the tank to keep the pump cool and lubricated. Just thought I'd throw that in there for you guys.

Good point. I was talking to a mechanic one day and he told me when it gets really hot out, and people don't fill their tanks up (now that gas is so expensive) they burn their fuel pumps up. He said the Ford Aerostar van is really bad for this.

[Danronian]

I try to fill up when I have around a 1/4 tank left since I know the sloshing of the gas can allow more air to get in the fuel pickup and decrease MPG. I always seem to get better MPG if I don't run it to the "e." That being said, it's right above the E right now... :( I've been pushing it off hoping that gas would go down a few cents.

[BBsGarage]

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.



Never heard of this. I can see if it is an older car that has been sitting around for a while and the fuel tank has started rusting, but otherwise theres not much gunks to be had. Plus most modern tanks are some type of plastic.

Personally I fill up when I hit a 1/4 because I dont like going to the gas station any more often then I absolutely have to.

[dkjones96]

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank, but I've heard that doing that is bad because you're not cleaning out all the gunk in the bottom of your tank and in the long-term, you will have to get a new gas tank.

The fuel inlet is always at the bottom of the tank, the only 'gunk' to be had would be stuff floating on top and since gasoline is so thin not much floats on it.

[PaleMelanesian]

The reason I'm asking is because everyone knows you get better gas mileage from a full tank to half a tank

That's only because the gauge is not linear. It doesn't mean you're getting better mileage. Almost all cars read above half for the majority of the time.

Here are my results from the last year. About 500 data points, logged from the Scangauge. My car has a little hiccup/stumble when it starts running low.
1267

[theholycow]

bringing the fuel too low will wear out the fuel pump faster. Most pumps actually use the fuel in the tank to keep the pump cool and lubricated.

Agreed, The fuel pump in my GMC died prematurely at 140,000 miles due to my habit of running it down to fumes before filling. Since then I try to fill at 1/4 tank, leaving enough to cool the pump but not having to drag around the weight of a full tank all the time.

That's only because the gauge is not linear. It doesn't mean you're getting better mileage. Almost all cars read above half for the majority of the time.

That's so annoying. I've observed it on vehicles from many manufacturers. Any guesses why they do that? It's not like you'll notice on a test drive that you're down to half a tank and have gone 250 miles. :confused: