# Gas Weight and Gas Mileage **URL:** \ **Category:** Factual Questions\ **Created:** [May 25, 2006, 6:03pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214 "2006-05-25T18:03:39Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![Hampshire](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/hampshire/32/4887_2.png) [@Hampshire](https://boards.straightdope.com/u/Hampshire)\ **Post date:** [May 26, 2006, 4:57pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214/21 "2006-05-26T16:57:09Z")
> [@Ludovic](#): > > Is there any truth to the notion that a fuller gas tank will help the pump get fuel to the engine via pressure? That never made much sense to me, and the notion that it would save fuel (in terms of not having the car’s pump work as hard,) versus the gas spent by lugging the extra weight seemed odd to me, but this is as good a time as any to mention that. Maybe with older engines but everything nowdays seems to have fuel injectors and fuel pumps so I doubt it. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [May 26, 2006, 5:33pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214/22 "2006-05-26T17:33:50Z")
> [@Ludovic](#): > > Is there any truth to the notion that a fuller gas tank will help the pump get fuel to the engine via pressure? That never made much sense to me, and the notion that it would save fuel (in terms of not having the car’s pump work as hard,) versus the gas spent by lugging the extra weight seemed odd to me, but this is as good a time as any to mention that. Maybe yes even with fuel injected cars. On some fuel injected cars, the main fuel pump is external to the fuel tank. Electric pumps push great, but don’t suck worth a damn. So to get the fuel out of the tank, the car makers install a pre-pump inside the tank to push the fuel out and supply the main pump. On some car the combonation of extreme heat, high fuel demand, and a low tank can cause a fuel starvation problem. Having a full tank does not “save” fuel in this case, but does prevents driveability problems. ---
**Author:** ![Omegaman](https://avatars.discourse-cdn.com/v4/letter/o/e480ec/32.png) [@Omegaman](https://boards.straightdope.com/u/Omegaman)\ **Post date:** [May 26, 2006, 5:47pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214/23 "2006-05-26T17:47:08Z")
I would like to second what Rick said. I see many premature fuel pump failures caused by running 5 dollars worth of gas in vehicles. Although I have no site , I can’t imagine that having a full tank would affect mileage an appreciable amount. I think considering the average price of pump replacement , even if it did save money, t would take quite a lot to offset the difference . ---
**Author:** ![spingears](https://avatars.discourse-cdn.com/v4/letter/s/ebca7d/32.png) [@spingears](https://boards.straightdope.com/u/spingears)\ **Post date:** [May 26, 2006, 6:47pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214/24 "2006-05-26T18:47:23Z")
> [@Spartydog](#): > > One of our idiot founding fathers (I think it was Ben somebody) made the absurd observation that “time is money”. Not that I have to believe it but some people do. What’s your husband’s time worth? Not much, I’d have to assume. > :smack: :smack: :smack: > It’s like driving 20 miles out of your way to save 3 cents a gallon. > [@Missy2U](#): > > … This results in me having to go to the gas station like every day. This also results in me being very annoyed. … Since it’s not his time it isn’t important to him. Get the mules attention with a 2 x 4 up along side his head. > [@Gary T](#): > > It sounds penny wise and pound foolish to me. It is. Amen! ---
**Author:** ![Balthisar](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/balthisar/32/2825_2.png) [@Balthisar](https://boards.straightdope.com/u/Balthisar)\ **Post date:** [May 28, 2006, 1:52pm UTC](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214/25 "2006-05-28T13:52:18Z")
As **Rick** says, the internal-to-the-tank fuel pump is a low pressure pump that delivers fuel to the high-pressure pump in your engine compartment. There are screens and filters to keep junk out of your injectors. The big particulates will stay in your fuel tank happily for years without any effect on your car. Water, though, is denser than gasoline and stays on the bottom of your tank, right where the fuel pump is. So it gets sucked into the fuel line with the gasoline. The amount of water is so miniscule that you and your car should never, ever notice it. Yeah, there’s condensation, but how much condensation are you talking about? Or is one of the neighbor kids filling your tank with liters and liters of water? In normal operation – even with those $5 fill-ups – the condensation is consumed. Your tank, then, is probably plastic, so there’s no rust to worry about. If you have a steel tank, it’s painted on the inside and there’s still no concern for rust. [Previous page](https://boards.straightdope.com/t/gas-weight-and-gas-mileage/358214.md?page=1)