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Go Back   ClassicBroncos.com Forums > 66-77 Ford Bronco > Bronco FAQ > Engine FAQ's

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Problems Filling the Gas Tanks(s) Problems Filling the Gas Tanks(s)
Problems Filling Gas Tank(s)

The Problem:
There are several difficulties commonly encountered when filling the gas tanks:
(1) Gas sloshes out if you try to fill the tank at a reasonable rate and can only be added veeerrrrrry sllloooooowwwwwwllllly.
(2) Variation on (1), the fuel pump shuts off when the fuel sloshes back or for no obvious reason, almost a though the tank is full.
(3) Gas dribbles out from underneath if you fill the tank all the way up, or there is a strong smell of gasoline for a while after filling up.

There is no consensus on what this common problem means but there are several candidates.

Gas sloshes out of neck (1) and (2):Probably multiple causes and variations are at play, but some sort of physical restriction in the gas filler hose or a pressure restriction in the tank venting arrangement may be a culprit. Obviously a kinked main filler hose could slow down the filling enough. It is not a common problem though. Usually there is no obvious restriction. So the next best bet is that there is a pressure restriction in the tank, that is, the air in the tank is not being pushed out fast enough for the fluid gasoline to come in. So the filler line may burp back when the air bubble rushes past the incoming stream of gasoline. There are other scenario. But the basic principal is that the tank is not freely vented.

Gas dribbles underneath (3): If gas dribbles out, obviously there is a leak somewhere, but it is not always the same cause. This is usually a problem with the auxiliary tank, the one under the drivers seat. There are 3 biggies. Listed in approximate order to likelihood
(a) One common cause is a small crack in the vapor line, the main fuel line, or, on later models, the carb-to-tank return line at or near the tank. Any of these can get a fine crack or just plain come loose. The small lines and vapor lines seem to be the trouble makers.

(b) Because many auxiliary tanks are plastic, over the years the plastic can dry out and develop stress cracks or even gouges from lodged pebbles . If a crack develops near the top of the tank, it will be apparent only after filling the tank, or only as faint gasoline smells. A lot of times the cracks are around the rounded corners of the tank. Some auxiliary tanks (very few) are metal and might have rust holes.
Sometimes the venting can get blocked and the tank gets sucked inward until if caves in and develops cracks. There are all sorts of ways for cracks to form, but age enhances the process.

(c) Another common cause is a crack or leak in the seal for the tank gauge sending unit. It is located on the side of the tank, so when the tank is full gas is sloshing or covering the seal full time. It is a wonder that it seals at all. This will be obvious if there are stains where fluid has dribbled along the side of the tank just under the gas gauge opening. It is not as common as you might think, although some people have trouble getting a good seal on the sender unit seals in newly replaced tanks or senders.
(d) Cracks in very old filler neck hoses can be pretty big and obvious, and most of the original ones will have them, but the filler neck rarely is a cause of leaks. It will be obvious if it is the source of the leak because of stains on the outside of the hose.

The Fix:
No real consensus appears to have developed to address this problem, but there are several things that can be done to help narrow down the cause in your particular case.

Gas sloshes out of neck (1) and (2): Assuming there is no obvious kink in the big filler hoses going into the tank, then one of the vent lines should be suspect. Start tracing hoses coming out of the tank. One of the lines is a vapor recovery line and it has a small check valve in it. Make sue that has not gone weird and plugged up for some reason. Or make sure that none of the hard lines that vent over to the charcoal canister in the passenger side wheel well have gotten crimped.

Some people claim that turning the gas pump nozzle upside down helps to mitigate against the pump shutting off unnecessarily. Others find that angling the nozzle slightly with respect to the filler neck helps keep the pressure sensor hole out of harms way.

If the original electric tank sender gauge switch and manual fuel line switch are in place, dont under estimate the ease with which you can confuse which tank is full and which is empty. I have had trouble filling an empty tank on more than a few occasions only to discover that I was trying to fill a full tank.

Gas dribbles underneath (3) Trace until you can find where the gas is coming from. If it is dribbling from one of the small lines that should be obvious. If it is coming from a crack in the tank it will not. So if a thorough search does not turn up an obvious candidate, and especially if the tank is a couple of decades old, assume that it is time for new tank. Wishful thinking will try to make you discard this idea, but experience says it is really a good bet as the source of the problem.  

Last edited by admin; 08/01/06 at 03:13 PM.. Reason: added byline
nebraskafootbal on 06/02/08, 08:23 PM
what to use? plastic or metal gas tank
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