Topping off Fuel Tank

[BSeevers]

Being the cheap and paranoid fellow I am...........................

My local gas station is associated with a large automotive/parts/tools chain. The store has had a reward program for the last 70 years, in the form of store cash coupons. The gas bar also offer the coupons, and include a multiplier coupon in thier weekly flyer.

Being a two car family, I fill up one vehicle and three 20L gas cans, using the coupon, and walk away with 2-3 dollars a fill up in store coupons. When the next vehicle needs fuel, I dump as much of the stored gas as possible into the other vehicle, and again fuel up the empty van and the gas cans.

In that way, I try to keep 60L on hand for emergencys, and rotate the fuel. However, I confess to being guilty of running too low.

Ok the real question is how many primers do you have and where are they?

[Y. Koester]

It is true. In some cars, it can fill the EVAP lines and the carbon canister, along with the rest of the EVAP system. In all OBD2 cars, the EVAP system is sealed. Some cars use leak detection pumps that pressurize the system. Other cars use engine vacuum to 'negatively' pressurize the system. Purge and vent valves then open and close to vent the fumes from the gas tank into the intake manifold. If the system gets plugged or a leak forms, the check engine light will come on to notify the driver there is a problem. By filling this type of system with liquid while it is meant to carry fumes, you can make the system think there is a problem, even causing permanent damage to components of it.

Moral of the story - don't do it. You may get away with it, but it's just not worth the risk.

I hate having to fix evap codes!! People leave their caps loose all the time. Plus if you ask them if they have left it loose lately, you always get a stupid answer.

[Canuck223]

Being the cheap and paranoid fellow I am...........................

My local gas station is associated with a large automotive/parts/tools chain. The store has had a reward program for the last 70 years, in the form of store cash coupons. The gas bar also offer the coupons, and include a multiplier coupon in thier weekly flyer.

Being a two car family, I fill up one vehicle and three 20L gas cans, using the coupon, and walk away with 2-3 dollars a fill up in store coupons. When the next vehicle needs fuel, I dump as much of the stored gas as possible into the other vehicle, and again fuel up the empty van and the gas cans.

In that way, I try to keep 60L on hand for emergencys, and rotate the fuel. However, I confess to being guilty of running too low.

Ok the real question is how many primers do you have and where are they?

Only 6k at the moment on the bench. 5k loaded on the shelf. It's mid season.

[Dave Gundry]

On the opposite end of the tank . . .

I have heard it's bad to run a tank down to the last few drops. Whether I like to admit it or not, I tend to let the tank get pretty low before I refill. I've had some folks tell me that running it much below half a tank is worse for the car than refilling at half a tank. I generally get down to less than a quarter tank before I visit the petro station.

Anyone heard of this? Is it legit? If I thought there was impact to my vehicle I might actually start filling up a little sooner.

Jack

This depends on the design of the system. You will hear different answers from (fairly) reputable sources. Most of the folks I've heard this from are talking about GM cars/trucks - some of which you are almost guaranteed a fuel pump failure no matter what you do. I believe that it doesn't really matter when you fill up - just don't run it dry. Every car I've ever had a pump out of has a pretty decent filter (strainer) on the pickup, and unless foreign objects/debris are introduced to the system, any modern car should have a pretty clean tank (i.e. not enough crap to clog the pickup strainer). If the pump runs dry, it can overheat. The electric motor is designed to run at a certain RPM range under a certain load. If it runs dry, load decreases and the pump speeds up.

The brushes and commutator are sealed in an in-tank electric fuel pump - it will not be able to ignite the fumes in the tank.

[Miranda]

good to hear the intank pumps have the brushes and commutators sealed.

the ones I fixed were not in the tank and the fuel definitely ran past them.

when I saw that, I decided that I was never going to run dry.

miranda

[noidlight]

A mechanic told me today to never top off my fuel tank in my car/truck beyond the auto shutoff because it will put raw gasoline into the vapor canister and cause major problems with the engine performance. I never heard this before. Thoughts? I have been cramming gas into my tank beyond full for 30 years.

Thanks

Your mechanic is right. The vents for the fuel tank are on top of the tank. If the vents fill with gas, from topping off, the fuel will go into the carbon canister and render it useless. This will throw an evaporative emmissions code, set the check engine light and cost you allot of money to fix. You will not be able to get an inspection sticker either, as OBD2 reddiness moniters will fail for evap if a DTC is stored. In short, DO NOT TOP OFF FUEL TANKS!! Also, do not fill when engine is running. If the PCM is running a leak check monitor in the evap system while fillin, the open fuel cap will prevent the engine from drawing a vacuum on the fuel system. The PCM will see this as a"gross leak" in the system and set a DTC (check engine light on)

[Sarge]

A mechanic told me today to never top off my fuel tank in my car/truck beyond the auto shutoff because it will put raw gasoline into the vapor canister and cause major problems with the engine performance. I never heard this before. Thoughts? I have been cramming gas into my tank beyond full for 30 years.

Thanks

Your mechanic is right. The vents for the fuel tank are on top of the tank. If the vents fill with gas, from topping off, the fuel will go into the carbon canister and render it useless. This will throw an evaporative emmissions code, set the check engine light and cost you allot of money to fix. You will not be able to get an inspection sticker either, as OBD2 reddiness moniters will fail for evap if a DTC is stored. In short, DO NOT TOP OFF FUEL TANKS!! Also, do not fill when engine is running. If the PCM is running a leak check monitor in the evap system while fillin, the open fuel cap will prevent the engine from drawing a vacuum on the fuel system. The PCM will see this as a"gross leak" in the system and set a DTC (check engine light on)

I have read enough here to not doubt what all are saying but I have been topping off forever and never had any of the problems described. But I must admit that I filled up today and only rounded to the nearest buck. Hard habit to break also.

[Miranda]

Hi sandman,

you have a car that handles being topped off.

there are cars that dislike that treatment.

the EPA made it very clear a few years back that auto fuel fumes are BAD for the enviroment.

among other things they decided to fight topping off fuel tanks.

this is because it causes avoidable fuel spills.

:-) stop doing it. the Government wants you to save your fuel.

miranda