disappearing fuel??

[akinodin]

I have a 2000 k1500. 5.3 vortec. I fill up the gas tank and drive. When I get home obviously I turn off the vehicle. When I start the vehicle usually next morning gas gauge has drained. Usually only a few bars. If I park the truck with a half a tank when I get in it to go somewhere few hours later it shows halfway between quarter and half tank. Any ideas where the fuel could be going or what may be the issue? Any help would be great as gas is expensive and I can't afford a quarter tank every time the truck sits.

[Dnt]

Maybe the neighbors kid is stealing gas? To prevent that just stop in at your favorite auto parts and put a locking cap on, easy peasy.

If that does not fix it then do a hand calculated fuel consumption test on your truck so you can verify check your fuel gauge operation.

On my wife's old beater van you have to hit the dashboard pretty firmly with your hand to make the fuel gauge read correctly hahaha

[Jsdirt]

I highly doubt that. It's just about impossible to feed a hose down inside the tank on modern vehicles (anything built after '95) - at least a hose large enough that you won't be sitting there for 3 hours waiting ...

 

Actually easier to disconnect a line and turn the key on. Not so easy for a thief.

[Dnt]

I highly doubt that. It's just about impossible to feed a hose down inside the tank on modern vehicles (anything built after '95) - at least a hose large enough that you won't be sitting there for 3 hours waiting ...

 

Actually easier to disconnect a line and turn the key on. Not so easy for a thief.

The neighbors kid can get a bunch of fuel with a 1/4" plastic line. Been there Done that and Got the Tshirt. All the neighbors kid or YOU need is a piece of PVC pipe and a couple different sizes of plastic piping. The obstruction in the filler neck is the rollover spill prevention valve and the 1/4" line will pop right past it. Once they get it flowing they go play a video game (probably "Grand Theft Auto") for a couple of hours and stop back in to get their bounty later...

[Jsdirt]

Ahh, good to know. I've never had any luck trying to siphon out of mine, but I was using 3/8" (I.D.) hose - pretty fat on the outside.

 

Diesels are very easy, though.

[silveradosid]

with fuel mileage that bad i would check fuel pressure regulator, they can leak and let gas get sucked into the intake

[akinodin]

I know it's not really disappearing. Lol but def not,getting,stolen either. The two labs in the yard make sure of that. I'm just trying to find where to start. I did the calculations. On twenty gallons I only made it 212 miles. Gas miles age is ridiculously gone. I,just had the tranny,rebuilt but that doesn't have anything to do with why my,gas is going. Its almost like a leak in fuel system somewhere but I,can't find one. Justput a new pump in it couple months back. The fuel system is pressurized so When I,cut the key off for a while and go to start it back it should still read half tank. Or least close. I don't really rely on fuel gauge more so than the actual mileage but some things up. Sorry about all the crazy in this my phone is horrible.

I know it's not really disappearing. Lol but def not,getting,stolen either. The two labs in the yard make sure of that. I'm just trying to find where to start. I did the calculations. On twenty gallons I only made it 212 miles. Gas miles age is ridiculously gone. I,just had the tranny,rebuilt but that doesn't have anything to do with why my,gas is going. Its almost like a leak in fuel system somewhere but I,can't find one. Justput a new pump in it couple months back. The fuel system is pressurized so When I,cut the key off for a while and go to start it back it should still read half tank. Or least close. I don't really rely on fuel gauge more so than the actual mileage but some things up. Sorry about all the crazy in this my phone is horrible.

[akinodin]

I'll try that first. I guess I'll put a fuel pressure test next

[Doug_Scott]

If you always back in to the driveway, pull in for a week and see if you notice any difference. I can also attest to the ability of the GM fuel gauges to adjust their level depending upon angle of vehicle. Used to be full size GM cars would show a fuel level that would swing from 1/4 to 3/4 if you went through a driving slalom. On my truck if I back into my driveway and the fuel light comes on, if I turn the truck around, and restart the truck, the fuel light does not turn on. Drive about 10km and the light will then come on.

 

Were it me, I would try all the free things first to find an explanation. Don't discount the gas gauge accuracy so quickly.

[Doug_Scott]

The neighbors kid can get a bunch of fuel with a 1/4" plastic line. Been there Done that and Got the Tshirt. All the neighbors kid or YOU need is a piece of PVC pipe and a couple different sizes of plastic piping. The obstruction in the filler neck is the rollover spill prevention valve and the 1/4" line will pop right past it. Once they get it flowing they go play a video game (probably "Grand Theft Auto") for a couple of hours and stop back in to get their bounty later...

 

The flapper valve in the filler neck is a restriction placed there to force attendent to use the lead free fill nozzle. To force the use of lead free fuel they reduced the size of the filling station pump and put the "flapper" in the filler neck to prevent the larger leaded fuel nozzle from being used. It is is no way capable of sealing off the filler neck. Most have vents around the flapper as well to help keep the fuel from being being sprayed out while filling the very top of the tank. When unleaded came out, no car with a carburetor/engine driven fuel pump had a shut off valve in case of roll over. Actually, they did have the carburetor that really only worked as a downdraft carb. Once upside down, it tried to become a up-draft.

[Jsdirt]

Thankfully I never got to test that theory, LOL!

 

I miss the wide-open filler necks on the old iron. Made transferring fuel from one vehicle to another super simple. Also required the use of the Stant locking gas cap, at least where I lived. Still have one on the '86 Grand Marquis, even though that one was built right around the lead ban time.

[Jsdirt]

Best thing to do is throw a scan tool on there, and see how the fuel trims and o2 sensors look. Tranny shop might've busted up the o2 wiring, or the sensors themselves, and it hasn't been driven enough yet to throw the light on.

 

Just a thought, but definitely need to see live data.

[Jsdirt]

Highly doubt it's "disappearing" - if it was, you'd smell it a mile away, especially in your driveway.

 

More than likely it's just "GM quality" gauges. Ever since I can remember, GM gauges have been lacking in consistency and reliability - even more so today.

 

If your driveway has a slope to it, it's going to read low if you're parked nose-down, and will stay low for quite a while. This is with a FUNCTIONING sender and gauge! My '07 has done this since day 1.

 

Their senders leave alot to be desired too - I've seen those fail in a very short time. In a nearly 17 year old truck, anything is possible there.

 

So what I'm trying to say here is, don't put so much faith in your gauges. If they seem out of whack, chances are, they ARE.