82 votes
Accepted

Top off gas with old oil, is that bad?

It's a BAD idea! The oil is contaminated with impurities that will not do the fueling system on your car any favors. Further, it's bad for the environment because your car is NOT designed to burn ...
  • 10.1k
46 votes
Accepted

Do cars consume less gasoline when the tank is full?

No. If anything you'll get worse gas mileage with a full tank because you're carrying a heavier load (more fuel = more weight). What you are most likely experiencing is the top half of the tank is ...
30 votes
Accepted

How to (relatively safely) store a small amount (200 milliliters) of gasoline for up to a month?

You can use a camping fuel bottle. They are usually made of aluminum, they are made to hold flammable liquids including gasoline, and they do not leak. I have seen them as small as 500 ml, and you ...
  • 1,618
29 votes

Small amount of wrong fuel type put in the tank

The main concern with using petrol in diesel systems is that diesel is used to lubricate the fuel pump, which petrol cannot perform adequately, which will shorten the useful life of the fuel system. ...
  • 39k
28 votes

Should I really keep my gas tank at least half full?

I'd suggest there's credence for all of these Your fuel pump overheating if it runs dry Unbeknownst to most, the fuel in the tank cools the fuel pump in most vehicles. The pump sits in a ...
22 votes

Why does stopping and starting a car in heavy traffic burn more fuel?

If you think about what the car is doing in both cases you'll see why you burn more fuel when accelerating. General theory F = mA (Force is equal to mass times acceleration), and in this case the ...
  • 9,286
18 votes

Driving on full tank

No. Vehicle weight is only one factor of fuel economy. The most important factor is air resistance. Vehicle weight comes as the second most important factor. My ~1700 kg (car + driver) Toyota RAV4 ...
  • 14k
16 votes

Why does stopping and starting a car in heavy traffic burn more fuel?

Every time you brake, the energy is wasted. Brakes convert mechanical energy of a moving car into heat via friction (they heat up). This is where the energy is ultimately "lost". Then, when the ...
  • 805
16 votes
Accepted

Small amount of wrong fuel type put in the tank

The main problems from misfueling a diesel car with petrol stem from the fact that (as Zaid points out) petrol doesn't provide the lubrication effect of diesel fuel and as a solvent it can actually ...
  • 9,777
16 votes
Accepted

Are these holes at the bottom of a 1965 VW Beetle Fuel Tank part of its design? Does something go there?

Those holes are not meant to be there. This photo of a new tank doesn't have the holes. The holes look like someone has drilled into the tank to remove the fuel at some point. Whether that was to ...
14 votes

Do cars consume less gasoline when the tank is full?

The best way to determine the actual fuel consumption is to brim the tank, drive till nearly empty then brim the tank again. Then you have an exact volume of fuel and a specific distance. Repeat over ...
  • 34.4k
13 votes

Top off gas with old oil, is that bad?

All modern cars scavenge blow-by including oil vapour and a mist of droplets. This is good for upper cylinder lubrication and does extend ring and bore life. If you have to, you can install a catch ...
  • 406
13 votes

Top off gas with old oil, is that bad?

Aside from the numerous reasons not to do this to your car I would like to offer you a solution to your perceived problem. Don't take the old oil back to the store. At least not right away... Your ...
  • 1,187
12 votes
Accepted

What is this pipe coming out of the petrol tank under the seat

It's a gasoline vent tube, serving three purposes. Gasoline vapors can be especially dangerous under pressure (pretty much why it is useful), and as the temperature fluctuates it is safer to relieve ...
  • 2,674
12 votes
Accepted

Why is there a hissing noise when I open my petrol cap?

Regulations limit the amount of unburnt hydrocarbons that can be released into the atmosphere, therefore fuel tanks on cars now have to be sealed to stop these emissions. The noise you hear is air ...
12 votes

Getting Stale Gas Out of a Gas Tank w/out Dropping the Tank

If there is under a gallon of stale gas and you filled your tank up with fresh, I don't think there'd be an issue with the stale gas. It would dilute enough you shouldn't have to worry about it. If ...
12 votes

Do cars consume less gasoline when the tank is full?

IF - the tank was uniform in its dimensions - vertical sides, etc., and IF - the gauge sender worked exactly in a linear manner, and IF - the gauge responded in that same linear manner, and IF - the ...
  • 428
11 votes

Small amount of wrong fuel type put in the tank

This will not be a problem - in fact, some of the older truckers used to add 2% of petrol to the diesel to help in winter conditions to help reduce waxing of the diesel fuel.
  • 34.4k
10 votes
Accepted

Does the mileage indicate the quality of the gas?

It is not likely the quality of the gasoline causing the change. The sensors are unable to evaluate the chemical makeup of the fuel. It could be a change in your driving habits, changes in temperature,...
  • 9,035
9 votes
Accepted

How can vehicles run on E?

The gas gauge is just an indicator and each vehicle is going to be different. I know the older Datsun Z cars had two gas gauges, one was the main one which showed the volume of gas down to 1/4 tank, ...
9 votes
Accepted

Is it necessary to turn off the engine while refuelling?

Here is a link from the API (American Petroleum Institute) website. http://www.api.org/oil-and-natural-gas/consumer-information/consumer-resources/staying-safe-pump The article is called Staying safe ...
  • 3,862
8 votes
Accepted

How easy (is it possible) for an amateur to change the drain tube of a motorbike fuel tank?

Interesting issue IF, the internal tubes have corroded within the tank that would be relatively serious. The interesting piece is, how would they corrode. As far as I know, almost ALL the fuel tanks ...
  • 32.8k
8 votes

Why does stopping and starting a car in heavy traffic burn more fuel?

Your engine is always burning gas when the car is running. When you're stationary, you are burning gas to keep your engine running, without actually moving the car, so you're actual miles per gallon ...
  • 6,017
8 votes
Accepted

Why does the engine have lesser pulling strength when the fuel in the tank is lesser?

It sounds like you have a motorcycle with a carburetor with gravity fed fuel line. (i.e. Without a fuel pump of any sort). In those conditions I can see that there is a higher fuel pressure at the ...
  • 6,529
8 votes

Are these holes at the bottom of a 1965 VW Beetle Fuel Tank part of its design? Does something go there?

Back in the day, it used to be possible (in the UK) to wander around a scrapyard and unbolt random bits off stacked piles of dead vehicles, and that was how I kept several cars going. Fuel tanks ...
  • 1,509
8 votes

How to (relatively safely) store a small amount (200 milliliters) of gasoline for up to a month?

One possibility is if you can find small engine gasoline / alkylate gasoline sold in a one-liter container. That gasoline burns very cleanly, can be stored for about 4 years with no degradation and ...
  • 14k
7 votes
Accepted

Is it bad on your fuel pump to have your tank run low?

Yes, running low on fuel can damage your fuel pump, but as IHaveNoIdeaWhatImDoing mentioned in the comments below, modern fuel tanks are sophisticated enough to prevent fuel pump starvation until the ...
  • 6,017
6 votes
Accepted

Fuel system question

That pipe probably goes to the tank too, it is just there to let air out of the tank while adding fuel down the main pipe. I believe that your additive will be in the fuel.
6 votes
Accepted

Leftover gas in the gas pump due to hose design

It doesn't really matter if there's gas left in the hose. The only way for all gas to flow out of the hose is for the hose to collapse or air to enter it. It's metered at the pump side but it doesn't ...
  • 4,910
6 votes

Can not fill gas into tank for 2004 Honda pilot

This could be a bad vent valve or a blocked vent hose located near the vapor canister under the vehicle. As this article states, A clogged up vent valve can cause trouble filling the gas tank. ...
  • 9,035

Only top scored, non community-wiki answers of a minimum length are eligible