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Mystery Mileage on a 2000 Chevie Astro

I have a Chevie Astro 2000, which I have owned since 2005 and now has approximately 175,000 miles on it…

The last two times I filled the gas tank (which has a very sensitive filling nozzle) I have a hard time believing my mileage.
I normally get 15 mpg, sometimes 16. MY gas gauge is shot and always shows full. I know I can get 395 miles on a full tank.
The last two times I have filled it, the mpg is unreal. (I use the trip mileage gauge to know when to fill, lol). The other day,
when I was filling it, I had driven 281 miles and it stopped accepting gas at 10 gallons I would click it again and only get
.03 gallon each time. The fill before that, I filled it till it was overflowing, so I know I had started out with a full tank.
Having done this many times, I got it up to 12 gallons, which meant I was now getting 24 mpg which
I know it’s never done before. The same thing happened the fill before. Is it possible to somehow get a vacumn in the tank or
something, since I should have been able to put 17 or 18 gallons in the tank? The van is garaged so I don’t think anyone could
have put something in the tank to lower the capacity. don’t say trade it because I m on Soc. Security and can’t afford to get
another vehicle. Help? lol

There’s no way you’re getting more than 19 or 20 mpg highway unless you’re driving down a mountain, or at 45 mph on the highway with a tail wind.

Something is preventing you from filling the tank fully. After driving 281 miles at, say 15 mpg average, you should have been able to add 19 gallons or so. Instead, the pump shut off at 10 gallons and you had to try hard to to reach 12.

Most likely the evaporative emissions system that takes vapors from the gas tank during fillling is plugged up. The air/vapor inside the tank has nowhere to go and prevents it from being filled fully.

You can either live with it, or take it to a mechanic and ask him to check for an obstruction in the evaporative emissions system.

You could also try using a different gas station. Sometimes different pumps will shut off later and fill the tank more.

Thanks for your response. Both of the fill-ups were at different gas stations as I had hoped that maybe it was just the one station’s pump. I will have it checked.

I also own a 2000 astro and it is picky when filling up - the pump always cuts off unless you hold the gas nozzel just right. Don’t even think about letting it cut off automatically when full, you will pump only a few gallons. I have driven chevy vans on & off since the late 1960’s and each I have driven has done the same thing. Just something you get used to I guess!

Probably not much help on your topic but I thought I would empathize. :wink:

The first time (abt 2 weeks ago), it did this at a Shell station. I held the nozzle all the way in with the rubber gasket against the fill pipe. I must have clicked it at least 50 times (abt .03 of a gallon
each time it shut off.) I knew it couldn’t be full as I had drive 300 miles and it was balking at abt 10 gallons again. I removed the pump nozzle from my the tank fill-pipe and abt 1 quart shot back out at me. I always manually fill it as auto never works as you say.

This time, I did not hold it in tightly since I didn’t want to waste any gas at it’s current prices. I have even thought of running a 1/4 inch plastic hose down into the tank while filling to see if that
would create an air vent while filling it. (Will do that the next time I am filling up)

6 years ago, I had to put in a new fuel pump and was kink of shocked at the cost so that is why I
have worked around the fuel gauge indicator, figuring it was gonna cost a lot more this day and age, lol.


We have tons of those Astros in our fleet and don’t have problems filling them. You just depress the trigger, put the lock in place and wait until it clicks off. And then you have a full tank.

If you have to use magic fingers, there’s a probem with your tank and/or evap system, as the others have already mentioned

You can get the float by itself, minus the pump

That said, I believe it’s false logic to drop the tank and only replace the float. If you’re going to that much trouble, you might as well spend a few bucks more and make sure everything’s good to go

By the way, I’ve replaced several of these pumps, and it’s not that difficult. A lot easier than on some trucks

“I have even thought of running a 1/4 inch plastic hose down into the tank while filling to see if that
would create an air vent while filling it. (Will do that the next time I am filling up)”

Don’t do that. It will only cause more liquid gas to spray out of the tank at you once the gas level reaches the bottom of the hose. Get the evap system fixed.

Part of the problem might be that, in some states at least, the owner is now responsible for adjusting the metering and calibration of the gas pumps. You may be getting over a gallon at some pumps but I’m seeing a possible future where you don’t. I’ve already run into one station that thinks a gallon is a little over 3 quarts. My calls to the proper channels at the state Agriculture Department just fell on deaf ears. I hear that the same problem is beginning to occur in a lot of states. Another problem is the multiplication of the price of the gas and the actual gas delivered. It’s always a higher dollar amount than what you were supposed to pay.

You should never fill the tank so full that gas comes out the filler tube. You can damage the evaporative system.

I have the same problem at a few places. Some I need to pull the nozzel out far enough for the air to escape thru the filler tube. THen the pump keeps running but still shuts off automatically when the tank is full.
I had one truck that, if I pulled in from one direction, I had problems. Pulling in from the other direction and there was no problems at all filling up.


Thanks for the info Yosemite. It was not my intention of overfilling the tank. When you have had the vehicle as long as I have and you know that you should be able to put in 17 or 18 gallons (because I get 15 mpg usually) and it shuts off at 10 to 12 gallons, that it’s not full. It was not my intent to leave 1/3 or 1/2 gallon of gas on the drive. As you can see, others with Astros have had the same problem with the auto shutoff and the filler tube so the auto shutoff is not an indication that the tank is full.


“As you can see, others with Astros have had the same problem with the auto shutoff and the filler tube . . .”

But some of us have told you that you may very well have a problem with your evap system

Yes, I appreciate your input. I thought it maybe something creating like a vacumn but since Im not that mechanical, that s why I was asking. Thank you.

It’s the opposite of a vacuum. You’re trying to add fuel to the tank and the air inside has no place to go because the vent line (actually the evaporative emissions recovery line) is obstructed, so the pressure builds up in the tank and pushes the gas back out the filler neck.