Any years Gas Tank Spitting Back

[smokuspollutus]

Hi guys,

Anyone else having issues when filling up? On both of my cars, the fuel overflows for a brief second before the pump clicks off. After talking to some other people with similar era cars (all with behind the license plate fuel necks with unleaded restrictor), we're all experiencing the same issue.

I have not had this issue on cars with the side fuel filler. Given a pretty large sample, I'm ruling out mechanical issues. My thought is, maybe the pumps have been recalibrated to be less sensitive given the anti siphon fuel necks on modern cars, and the shorter neck on our cars doesn't give it enough "warning" before it clicks? For now we've all taken to just filling up slower towards the end and listening for the sound change, but this still frequently gives a little splash back. Annoying, especially when it comes to elderly bumper fillers & associated body work.

Anyone have insider info as to why this is? Easy modifications that can be made to stop it?

["Cadillac Kid" Greg Surfas 15364]

Not having this issue on either of my cars with the neck restrictor I would vote for the pumps as the culprit. Try fueling at a slower rate and see if that makes a difference
Greg Surfas

[signart]

Clear your vent tube

[J. Russo]

I have to fill my '41 slowly or it will spit back even if the tank is low on fuel.

[Mike Baillargeon #15848]

It happens to a couple of my cars also....It seems to happen to the cars that have after market fuel tanks.....they probably don't have the baffles the original ones have....

I think that when I pull into the gas station and pull up to the pump the gas that's in the tank is still sloshing around blocking the vent and then the fill pipe causing the spitting back....

If I wait at the pump for a full minute before filling up, the gas goes in a lot easier...

Just my 2 cents....

Mike

[smokuspollutus]

I had initially thought vent issues too. On both of my cars I have replaced the sending units (original tanks) but never noticed excess pressure/vacuum in the tank that would suggest vent problems.

Just found it odd that most everyone I spoke to with a GM car of the era was having issues. Maybe it's a regional thing with our pump calibrations in the northeast?

Slower refueling does prevent the problem. Not really an issue when you do your own but gets to be annoying when filling up in NJ where you have to have a petroleum professional pump your fuel.

[TJ Hopland]

Have you tried different angles on the nozzle.  I have found on some cars and some pumps you can find a position where it will be happy.

It is very strange that on these old cars we have like a foot long 3" tube and we have issues yet on modern cars the tube is often several feet long and includes a few twists and turns and those work. Its probably because on the new ones they have no choice other than to highly engineer it to have the perfect flow around all the bends. 

[signart]

Have you tried different angles on the nozzle.  I have found on some cars and some pumps you can find a position where it will be happy.

It is very strange that on these old cars we have like a foot long 3" tube and we have issues yet on modern cars the tube is often several feet long and includes a few twists and turns and those work. Its probably because on the new ones they have no choice other than to highly engineer it to have the perfect flow around all the bends.

That tells the tale right there. Several feet of tube vs 12" of tube says the air above the fuel has to go somewhere. If not vented, it's going out the filler neck along with some fuel, sometime violently. A long filler tube and vent plus a tank well below the tank prevents this occurrence.
The short tube that is inches above the tank must be properly vented other than the filler neck.
OP doesn't say what vehicle this occurs on, but cars with filler necks of the sixties behind the license plate have one, two or three or more vents and did not spew back when new.

[Michael Petti]

Worked pumping gas 1st job out of high school mid 60's. All those short neck tanks spit gas even if new if you filled them too fast. Air had to go some place. 

[TJ Hopland]

One thing I wasn't expecting when I was working on my 73's tank was that the filler pipe extends at least half way into the tank.  I'm not sure what difference it makes or if its got holes or baffles in it along the way.   60's and older stuff I have been into as well as aftermarket tanks its just a nipple on the outside of the tank as you would expect. 

[smokuspollutus]

Should have mentioned the year, in my case '83 Deville and '84 Eldorado. Spoken with people with a range of 70s-90s with rear mounted filler and were all having the same issue. Mine would be "vented" thru a charcoal canister. Not sure when that appeared but I would figure late 60s or definitely early 70s.  I don't remember this happening when these cars were in daily service 20 years ago, so I was figuring something had to change with fuel pumping considering a bunch of us were having the same problem.

Going to try to open the two vent tabs at the top of the filler neck a little wider on the Deville before the next fill up and see if that changes anything.  If no effect, I guess time to pop the 1/4" hose of the sender and canister and blow it out to see if there's an obstruction. I feel like the EVAP system is working fine as I've never had excessive pressure or vacuum in the tank or vapor smells. This era has a 3 legged sending unit (supply, return, vent) with no other vent points on the tank besides the neck.

[Daryl Chesterman]

Mr. Molinaro, there may be a filter on the bottom of the vapor canister that is plugged up and contributing to the "spitting-back" problem, or it may be that the charcoal media in the vapor canister is getting plugged up.  If you do try to blow back through the canister, I wouldn't use a lot of pressure to do so.

Daryl Chesterman

[smokuspollutus]

Thank you. Yes, I have heard that the charcoal canisters are ideally not trifled with if it can be avoided. If the filler neck vent is not enough, I'll try to disconnect and blow out both ends of the vent line and hope it's just an obstruction in there. I'm never that lucky, but I'll give it a shot.

[TJ Hopland]

I don't think the charcoal canister vent does much when it comes to filling the tank.  Its a pretty long 5/16" line so at the typical fill rate I would think it would take like double digit PSI to move that sort of volume through there.   I think the primary vent method is through the neck, many have a baffle near the top that is supposed to leave that area dry so the air can flow out.  80's I think they started doing like a 5/8 line from the tank that ended just behind the restriction plate that was mentioned earlier.   

[smokuspollutus]

After opening up the two vent slits a bit more, I have not had any splashback. I've filled the tank at full speed twice now from roughly 1/4 and both times the nozzle clicked and shut off the gas before any spillage happened. Both times at the same station, I'll report if anything changes as I travel. But for now I think this case is closed.

Thank you everyone!

[Chopper1942]

All fuel tanks are vented. Until EVAP systems where added in the 70's, the fuel tanks had a vented gas cap. The caps did not seal tight to allow pressure build up to escape as the fuel expands in the tank and allows air to enter the tank as the fuel pump extracts fuel from the tank. These tanks usually do not have a separate vent line. When you fueled the vehicle, the pressure created during fueling escaped through the fill pipe.

The purpose of the EVAP system is to lower emissions by capturing the fuel vapors from the fuel tank. When the EVAP system with a vapor canister was added to vehicles, a non-vented gas cap was installed on the vehicles. The purpose of the vapor canister is to capture the gasoline vapors as the fuel in the tank evaporates or expands because of temperature increases. The activated carbon particles capture the fuel vapors. When the engine is started vacuum pulls the vapors out of the activated carbon and burns it in the engine.

If you are old enough, like me, you remember that the fuel nozzles did not have the small opening and tube inside the nozzle. You had to hold the lever on to get fuel. They did not have the notches and lock for the nozzle valve.  When the lock for the nozzle was added there had to be a method to shut the fuel off so it didn't spill out onto the ground. A port and tube was added to the pump nozzle. This vent allow the pump nozzle to shut off when the fuel is spit back up the fill pipe.

Because the canister is located in the engine compartment and the vent hose is small, another vent tube was installed on the fill pipe. This was required because of the volume of vapors being pushed out during refueling.

The vapor canister has no effect on the fueling of the older vehicles. On the new vehicle with a closed EVAP system, a plugged canister or its vent will cause slow fueling.

Many states have added vapor recovery to the fuel pump nozzles to capture the fuel vapors that escape the fuel tank during refueling.

Usually the reason for spitting back during fueling is that the nozzle is not installed far enough into the fill pipe or is not positioned correctly so fuel splash does not enter the nozzle port. 

Most of the OE tanks or fill pipes have a baffle to help prevent back splash during fueling. If they are missing, this can also be an issue. The older vehicles do not have them.

[79 Eldorado]

Anthony,
I sometimes have issues seemingly more associated with particular pumps. I assumed there was something in the pump shut-off which could be adjusted. I really fill slowly now though because I don't like when they spit. I also reset the trip odometer when I fill so I normally have a good idea how much will be required (check the trip OD before filling). If you're in a quiet enough area you can also hear a difference when they get close to full and then back-off.

Most of my cars are rear fill.

I'm having what I believe I've diagnosed to a fuel delivery issue in the Eldorado so tonight I was emptying the tank rather than filling. Unfortunately the job continues tomorrow. I can say 1000% I would rather fill than drain. I had a plan to minimize the issues, including blocking off a hose with a clamp designed for restricting a hose, but I still had fuel run down my arm to my shoulder... no fun. I don't mind gasoline powered cars obviously but I hate opening fuel system with fuel.

Scott

[Chopper1942]

If you are draining the tank on a '79 El Dorado with EFI, remove the hose from the high pressure pump, disconnect the connector at the rear of the tank. Run a jumper wire from the battery B+ to the light blue wire on the tank side of the connector. Unless you have a in-tank fuel pump issue, you should be able to drain the tank.

[Jay Friedman]

My '49's gas tank filler pipe will spit out when filling it up when the gasoline gets to the top.  I noticed, however, that when filling I can hear the liquid fuel flowing into the tank. Just before the fuel gets to the top, the sound of it flowing stops.  If I release the handle of the pump at that moment the filler pipe doesn't spit. Why? Haven't a clue.

[79 Eldorado]

If you are draining the tank on a '79 El Dorado with EFI, remove the hose from the high pressure pump, disconnect the connector at the rear of the tank. Run a jumper wire from the battery B+ to the light blue wire on the tank side of the connector. Unless you have a in-tank fuel pump issue, you should be able to drain the tank.

Larry,
That's how I ended-up doing it. I wanted to test the pump anyway. I had forgotten to bring my 12V source night one and the tank was draining so well by itself with just the high pressure pump I just let it drain. My power supply is all set-up with alligator clips and a switch. I know I could have used the battery etc but working alone I wanted to be able to see and hear everything with a smooth on and off using a switch. The next day I just brought my 12V power supply. I simply clipped the alligator clips to the high pressure loose wire terminals after removing the high pressure pump.

I may have been premature on emphatically preferring filling... as I took fuel out I needed to put it someplace as I didn't have enough can capacity. I was pouring it in my truck but every can I used other than my tiny 1 or 1.5 gallon can wanted to leak around the neck while I was trying to empty into the truck. They spend so much time on designing to not allow vapor and yet the necks are terrible. On top of which, with a license plate fill, the new style vapor containing release is near impossible to use without spilling fuel. I had to buy a new small tank about a month ago and I spilled so much while trying to use that on a rear plate car I didn't bother bring it with me.

Scott