Gas gauge issue/question

[hbsurfer]

I have noticed that after a fill-up and then 20 miles of driving the gauge shows 3/4 of a tank. That seems odd to me. Also, the gauge seems to drop rapidly and shows Empty (without light) and still has approx 5-10gallons left?? Is this common? I know the LC doesn't get the best mileage but?
OH, my LC is an 04 with 65,000,the only engine mod is the TRD air filter.
any and all suggestions would be helpful.

 

[LXPearl]

Seems rather quick. Mine have been a slower to 3/4 tank (80 miles). On E, it usually has 5 gal left. The 1/2 is likely the only accurate spot.

 

[Jim_Chow]

Mine also hits 3/4 after at least 80 mi of driving. I typically fill up at 1/4 tank and put in 16-17 gallons.

 

[hbsurfer]

The tank is 25 gallons right?

 

[KathmanduCruiser]

Mine hits 3/4 after around 40 - 50 miles of driving only.

Also, I have never gotten more than 14.5mpg even on highway driving. It is usually 13-14mpg. Could it be because it is ungodly cold here and fuel consumption is more when cold. I do not drive aggresive at all.

 

[hbsurfer]

as far as mpg so I have been avg'ng round 13 myself but got 16 coming home from Mammoth cruise control @72mph, needles to say I was pretty excited

 

[_JP_]

mine was just above E when i filled it up just now. got in 19.5 gallons. guess they set up the gauge to make it tough for people to run out of gas.

coming home from bishop i got 16.5 (per computer) and that was with several trips from bishop to pleasant valley and a bunch of driving on back roads and what not messing around the lower owens. cruise was set at between 74-76 all the way back. once we hit the 14 to 5 to 405 transitions i noticed that i was going 85 sometimes. the mileage made me pretty happy. i'm guessing without the screwing around in the snow and mud, i'd have been close to 18.

like the other guys said, i'm probably 60-80 miles in before it shows 3/4.

jp

 

[LX470Pilot]

I'm a naughty boy when I fill up, I really fill up. I'll put in $2-$3 AFTER the pump pops off as being full - haven't spilled yet.

When I get in, the gauge is slightly above F, I reset the Trip A odometer, and I know I'm being too heavy on the pedal if I haven't reached 90-95miles by the time the needle is at 3/4.

I use cruise control whenever possible, set between 70-75mph.

The most I've ever gotten was all highway from Pasadena, CA to Big Sur (just below Monterey) we pulled into the campground at 12am with 345miles on the trip odo, and the light had just come on about 5miles before. So theoretically, had I pushed to the bottom of the tank, I could have squeezed 400miles out of it - but I was nervous enough as it was - I hadn't planned that.

Note to anyone else who tries that trip - if you stay on PCH all the way up, be sure to get there before about 8pm or gas up in Pismo, cause all the gas stations between Hearst Castle and Carmel are close after then.

BTW - I've never tried them, but do those $4-$5 bottles of octane booster really do anything?

-LX Pilot

 

[hoser]

Mine goes down to "E" after about 250 miles... then I press the little "Aux Tank" button and it goes back up to "F"

 

[ebod]

Don't overfill

Hey LXPilot, I think I read on this board that putting gas in after the pump's initial auto shut off is really bad for your fuel pump and will, eventually, lead to expensive repairs.

I have no idea if this is true, but I don't top off just in case.

 

[LX470Pilot]

Hey LXPilot, I think I read on this board that putting gas in after the pump's initial auto shut off is really bad for your fuel pump and will, eventually, lead to expensive repairs.

I have no idea if this is true, but I don't top off just in case.

I appreciate the concern, but after a search, and reflection, the issue you present doesn't seem to make sense.

The fuel pump pushes a column of fuel up to the injection ports (as I understand it), so the major cause of stress on the pump is working on the fuel against gravity - but even then, the stress is minimal because the column of fuel being acted on is so small (anybody have the fuel line diameter?) so the major stress is just continuous use and wear.

So it seems to me that the only potential issue from topping off would be the extra pressure being exerted on the backside of the pump, because of the column of fuel above the 'level' point of the rest of the tank.

If the line from the gas cap to the tank is 1" in diameter, and 24" long, it will hold a total of 0.08 gallons. If gasoline weighs approx. 6lbs/gallon, we're talking a hefty 0.48lbs of force in that line from the gas cap to the tank.

Now, 0.08gallons is nothing, so why bother topping off?
As I said, I regularly put in $2-$3 worth (about a gallon) additional into the tank, after the gas pump initially pops off - obviously it doesn't all fit in the filler line (by the way, 1" is a completely random number, I'm just guessing from the size of the pump nozzle).

So I'm hypothesizing that the majority of the extra gallon or 2 that I squeeze in, is settling in the fuel tank itself which the pump is designed to handle fuel from.

If I'm off with any of this, or if anyone can offer a case where filling past where the pump stopped has proven detrimental in any way other than environmentally (fuel spill) please share. At the moment I'm inclined to think of it as a myth.

-LX Pilot

 

[KathmanduCruiser]

I have heard in different car forums how bad it is to stuff as much gas into your vehicle as possible. But none of them, I recall, seemed to give any conceivable reason. I am curious.............. Old wife's tale or a bizzare fact?

 

[hoser]

The reason for NOT topping off your gas has more to do with oversaturating the vapor recovery system. Our charcoal canisters aren't cheap either.

 

[LX470Pilot]

At the moment, I say old wives' tale - just trying to prevent spilling.

Think about it - the place you hear about not topping off is the gas station - signs along with no cell phone use (which is also bull - if you want more info on that one, check out www.snopes.com) - even the requirement of turning off your engine seems suspect to me: I'm a pilot, and I've seen several operations where they hot-swap seats (change out pilots) and refuel with the engine running - in both piston and jet engine aircraft.

Now, I have no problem turning off my engine, since sitting at idle at around 1000rpm for a full minute burns more fuel than cranking the engine again - but I'm really not sure that *just* having the engine on creates a hazard. I also shutdown my aircraft when refueling - it takes a measurable amount of fuel to start up again, but spinning rotors are just a bad idea around the fuel trucks and anytime people are going to be moving around the aircraft.

In case someone wants to give me flack about the other signs of no smoking and don't fill a container sitting on/in the vehicle: I agree with those whole-heartedly. Automobile gasoline has a relatively low ignition point, and vapor can ignite easily from a cigarette butt and a static-electric discharge.

*I think the biggest issue with having a vehicle running while fueling is the chance that it could slip into gear, or something to that effect.

**I'm remembering a list of things to do to increase mileage, and Avoid Topping Off was among the points - I have absolutely no idea how putting in less gas will get you better mileage though (other than decreased weight, but we've already seen that to be minimal), so if anyone could explain, I'm very interested.

-LX Pilot

 

[LX470Pilot]

Vapor Recovery System on the vehicle or the gas pump?

 

[hoser]

Vapor Recovery System on the vehicle or the gas pump?

Vehicle.

**I'm remembering a list of things to do to increase mileage, and Avoid Topping Off was among the points - I have absolutely no idea how putting in less gas will get you better mileage though, so if anyone could explain, I'm very interested.

I believe the idea is when topping off, the fuel can 1) spill out or 2) return back into the gas station pumps' vapor recovery system and so you are paying for the gas but some of that gas is returning it into their system.

 

[LX470Pilot]

But the list is about mileage, which to me is miles per gallon, not miles per dollar - so I understand your point, but it wouldn't seem to mesh with increasing the performance of the vehicle, just your wallet (which is also important).

If the gas vapor in a in a fuel tank is displaced and adsorbed into the charcoal cannisters while refueling (Onboard Refueling Vapor Recovery on model yrs 2000-present), and then desorbed to the engine inlet manifold during operation, not much would be going back to the station pump vapor recovery.

How long do the charcoal cannisters typically last? Anyone have a before/after ORVR comparison?

 

[hoser]

Well, even though you paid for 20 gallons, you only recieved 19.9 gallons and your fuel mileage calculation will be based on 20 gallons--that's the bottom line. I'm saying it's actual fuel that is going back into the station's vapor recovery system, not just vapors. It might not be a lot but there is some amount. It's not my point/argument, I'm just trying to explain why they say this.

Charcoal canisters can last the life of the vehicle but getting them wet/saturated even just once can render them useless and impossible to "dry out."

 

[LXPearl]

As hoser pointed out, the reason to not overfill the tank is to keep the vehicle's emission system working properly and efficiently. If the gas gets too full, it takes fills the recovery route to the charcoal cannister. When you start up, the canister will be already saturated so it is unable to absorb the rich starting mixture - so you pollute the environment unnecessarily.

As you use the gas the vapors will recirculate through the cannister to the tank, but it will take longer to dry the cannister enough to handle the next cold start. While the charcoal canisters are designed to last a long time, they were not designed to work with overfilling on a routine basis, and I would not be surprised if the system started causing problems.

I usually add a little in more in a tank after the first auto off, usually to round off the sale to a full or half dollar amount.

 

[hoser]

I usually add a little in more in a tank after the first auto off, usually to round off the sale to a full or half dollar amount.

Do you also add candy at the grocery checkout to round out the sale to the next dollar amount?