Rob delta

83 Delta 88 307

Hey guys,
I finally got the car back on the road a week ago. I painted the underside, changed the shocks, the differential oil, /new battery, and installed a new gas tank. I put in about 3-4 gallons of gas from a gas jug into the new tank, just enough to get me to the gas station. When I went to put in more gas at the pump, I could only pump for a few seconds at a time until the gas backed up and out of the fill tube. I ended up only putting in about 3/4 tank, didn't want to fill it until i knew everything was fine. I thought maybe there was excess air from the tank being so empty. In any event, the car ran great all week on the gas that was in there.
Today I tried getting more gas again, sure enough the same problem. My canister line is clear, i have a new purge valve(less than a year old). Is this a venting problem? I looked into the old tank and see there is a baffle at the bottom of the fill tube. Could there be something defective inside the new tank? I also have a new gas cap, both new and old are non vented as far as i know, not really sure if the cap would even matter as it's off during filling anyways.
I'm really dreading the thought of having to drop the tank all over again...
Any help is appreciated
Thanks,
Rob

Allan R

Rob,
what you're describing sounds like air locking. Does the new tank have the OEM baffle? If not I'd suggest that may be your problem. BTW, IIRC all cars after 1971 had vented gas caps.

If you do have to drop the tank, at least it will be easier and faster now that you know how to do it.

Rob delta

Hello Allan,
Well it's a spectra tank. From the research I did before buying it, it seemed like they are well built. I'm not sure if it has the baffle though. I guess it's my fault for not looking into it before putting in the sending unit and installing the tank. It's the first time I've done a gas tank and I was sure to compare the new and old one thoroughly as far as the contours on tank and bends on fill tube, etc. But never thought of the baffle inside.
Spectra claims it's identical to the OEM tank, but who knows without seeing inside now.
On a side note, I just thought a vented gas cap meant it's able to vent vapors to the atmosphere, and since i have the canister it would be a closed system. Now if a vented cap means it can let air into the tank but not out (to prevent vacuum build up), then I understand and i guess i do have a vented cap.

The tank is a Spectra GM411A. Would anyone know if this has the baffle inside?

Allan R

Hi Rob,
Spectra is a well known manufacturer and does build a quality tank. I'd suggest using their 800 number to ask them the technicality on your concern. We can speculate a lot, but they should be able to understand your concern and respond accordingly. See what they have to say.

Just out of curiosity, where is the baffle on the old tank? Can you take a pic that shows it? And I know exactly what you mean about dropping the tank. I did mine for the first time too! Fun isn't it?

Rob delta

I called spectra, the tech said there is a piece of metal that blocks off about a tenth of the filler tube. This allows the vapors to escape while filling the tank. He said I can either try to go back where I bought it and get another one under warranty or take a long screwdriver and try to bend this piece upwards. It has to be bent upwards where the filler neck curves before going into the tank. I guess the piece is bent open to far and allowing gas to enter and go up the filler neck. Since it's all internal, it has to be done blindly and I really won't know until i try getting gas again. Doesn't sound too promising, but i guess i could give it a shot.
Any thoughts?

Rob delta

So I just checked. This baffle is only a few inches long and it's right past the tab at the top of the neck. It doesn't appear to be bent down much more than the one in the old tank. Maybe the vent slits at the top need to be enlarged to let more air out?

frankr442

Baffles usually only control fuel sloshing around in the tank. Vapor won't be significantly affected by a baffle unless it's virtually closed shut. Are you sure all your hoses are connected correctly?

Allan R

I don't think you want to be playing with the tank, especially when it's got fuel in it. I'd be inclined to give the seller a heads up that its coming back as a warranty - and let them know Spectra suggested it. Once you start modifying the tank from what was delivered, a seller can say you were the one who caused the problem. Seriously, drain it and replace it. I'm guessing you have the 83 CSM or took pics of the tank before you removed it? I still lean toward the air locking theory.

Rob delta

Yeah I'm not going to alter the tank, plus they'll try to blame me for the problem. I did try bending that piece in the filler neck a little, i doubt that it will help though. It's not like I can stand at the pump and keep bending it more and trying out pumping gas to see if it spills out. Also in New Jersey we don't pump our own gas. It just so happened the station i went to had a considerate attendant who stood there and pumped the gas nice and slow so it wouldn't spill over.
BTW I got the tank at autozone because they had one in stock and I was able to check it out before buying it, instead of through the mail. I will see about the warranty. If i do have to drop the tank again, i'll be sure to use as much gas as possible this time. Last time, it was an afterthought as I was already working under the car and the gas tank became part of the MAWs when i saw the condition it was in. It was more than half full an i had no choice but to siphon

Rob delta

So I've spoken to a mechanic and other mechanically inclined people and we all seem to agree it's a problem of venting. It can't vent out the existing air and vapor as fast as the new gas is being pumped in which is creating pressure within the tank and spraying gas back out.
At the end of the filler neck you have the spring tab where the nozzle is inserted. Just above that there are two very small slits. The original filler necks have two slits and two holes about 1/4" in size. Since there is no other means of venting, I assume this is the only way for the air to escape when filling up?? Could it be that these two small slits are just not allowing the air to escape as quickly as it would if there were also two holes as on the original??
Just hoping for any thoughts before i go trying to enlarge the openings
Thanks,
Rob

Allan R

What you say makes perfect sense. How are you planning to make the 2 holes? I wouldn't drill, I'd use a sharp punch.

Rob delta

Between the metal shavings and possible sparks from the drill motor, i'm hesitant on using the drill too! Problem using the punch is I don't want to distort that thin metal before it pierces through. The large hole for the fuel nozzle plus those two slits probably already weakened it. If only I knew to make these holes before I installed the tank

Rob delta

I'm attempting to put up a pic. This is as much as the slits can be opened up with a flat head screwdriver. I wonder if this alone would be enough to get more air out. They were originally only opened about a third of the way. There's not really much area to make new holes. I'd have to try and squeeze two small holes above each slit if need be. I guess the only way to know if it helped is to try and fill up again and hope for no spray back

Allan R

Not sure from the pic, but what about that little slit at the top? Can it be opened a bit? That's an awfully tiny looking vent.

Have you tried filling the car with gas since you opened those other two?

Rob delta

That tiny slit at the top is actually the spring tab that covers the nozzle hole. It's the pivot point. so i wouldn't be able to make a hole in that immediate area. i can only try to make holes towards the outsides of those slits. I have not tried getting gas yet. But you can see what I mean about using a punch, it might distort the other openings

Rob delta

Allan, it seems to just be you and me. Thanks for your help, don't mean to be a PITA about this but it's just a little frustrating.
So in case you were wondering here's a pic of the old filler neck, two holes above two small slits.

Allan R

Rob,
With the amount you've increased the size of those 2 slits, I'd bet there's going to be enough venting to make it work. I agree it looks less than attractive but at this stage of the game if it will let you pump gas without air locking? Leave it the way it is. Please try putting gas in and LMK how it turns out. I'd bet it will work fine now.

greenslade

to enlarge those vent holes you could try using a large screw,just start the screw in the vent holes and screw it in,it will force the hole open,just a though.good luck

Allan R

Never thought of ^^^ that! Very smart idea. I must be a very smart person - according to your sig line.

Rob delta

I put gas in it at two different stations. I only put in about 3 gallons the first time and it didn't overflow. I thought it was fixed. Then I got gas again yesterday and it overflowed. The slowest auto setting on the nozzle was too fast for the tank and it would overflow after a few seconds. However it wasn't as bad as before I enlarged the holes so I guess it helped somewhat. I had to stand there holding the nozzle at a slow flow to not have it back up the filler neck. This makes it seem like there is some internal problem, either inside the filler neck or the baffles inside the tank at the base of the filler neck.
In the end, I can just live with it every time i get gas or drop the tank again and hope the replacement one doesn't have the same exact design and have the same problem. It's just crazy to think I went from a rusty tank that never backed up to a shiny new one that spews gas.

Allan R

There's something functionally wrong with the tank. I'd seriously consider draining it and taking it back for a new one. Just let them know what you've done to try and remedy the problem. No reason in the world you shouldn't be able to pump gas at a normal flow rate.

Rob delta

I just keep thinking I'll go through the trouble of getting a replacement and putting it in and what if it has the same problem since it's the same manufacturer (Spectra)
Allan, you said you changed your tank recently. Was that a spectra tank also? Does it have the same design as my filler neck with the venting as baffles? I assume you don't have a problem filling up so maybe there is hope with a new one

Allan R

Rob, yes it's a Spectra GM34R. The design of the filler neck is completely different than yours though because back in 72 the tanks were made to fit the wide nozzle tetra based fuel pumps. There is a flow baffle with a large opening in it closer to the top than the OEM, but IMO it will actually allow gas to flow faster than OEM.

My tank is still waiting to go in because I'm doing a full resto of the rear brakes and differential. Should be in hopefully this next week.

Here are some pics comparing the baffle in the new vs OEM.

Rob delta

Well my filler neck has the same baffle as yours, but like you said I have the extra piece covering it with the smaller hole for unleaded gas nozzles. In fact this baffle was what the tech from spectra mentioned. He said it may be bent too far down (the inside end of it) and I could attempt to stick a screwdriver in and bend it upward. Without knowing where it ends and not being able to see past the curve, that's pretty much impossible. I'll see about getting another tank under the warranty but like I've said before, I really hope the new one works without having to alter it again.

Allan R

In retrospect that's actually funny. Did you notice how the OEM tank literally almost goes to a point of constriction?

Rob delta

yes I see that in your pic. And even so I bet you were able to fill it for years with no problems.

Allan R

You would be exactly right. It would fill flawlessly even at full pump speed. I'm not sure why there's such a difference between the old and new. I'll prolly find out when I go to fill it for the first time. I'll keep you posted when that happens.

Rob delta

I have an update on the tank situation. I was able to get a new replacement tank under the warranty. Last Friday, I went through the process of draining, removing and installing the new one again. I went to get gas right after. I was able to put in about 14 gallons without a problem. This was a good sign but I still wasn't convinced. Today I went to the station where I had the problem last time. Sure enough it couldn't handle the flow of gas and it overflowed. Now in my opinion it seems like their pumps flow at a fast rate, even when lightly squeezing the nozzle. I still don't think I should have a problem though, the original tank was fine at this station. It's hard to believe I have yet another defective tank, but I've checked everything else.

Allan R

Do you still have the original tank? If yes, consider removing the filler neck and transplanting it to the new one. Only think I can think of that would make the 2 of them identical.

Interesting detective work. I have not turfed my old tank yet for exactly this reason. Sorry to say, but thanks for being the 'test' subject. Avoid that gas station and all should be ok.

Rob delta

When you're ready to install your new tank, I do hope it works fine. I'm sure not all of their tanks are bad.
After taking the time to do all this other work, it's pretty aggravating to end the project putting in a defective tank, twice. I just did some research on spectra tank problems. I seem to find a lot of complaints about filler neck not lining up behind fuel door. Many of them include the tank being called a "POS". That's not too far off from what I now think of it!
I do still have the old tank, so I could take the neck off if need be. Spectra sells the tank without the neck also. I feel like they should pay for the cost of having it attached to the tank if that's the route I end up going.

johns59super88

Rob, is the problem only occurring at one gas station? Is it possible that the gas is coming out aerated like a kitchen faucet? I've experienced this on diesel pumps when filling my rv. Have you tried other gas stations?

Rickman48

Used to be you could switch filler tubes without any kind of welding - there was specific hose and clamps for this situation, as tanks were the same, but fillers were different.
I, too, would do the switch.

Rob delta

John, the first new tank overflowed at 2 out of 3 stations. The current new tank took about 12 gallons without a problem at a different station. So I figured I'd test it out at the known to overflow gulf station. Sure enough it did. It could be aerated for all I know, it did seem to flow quickly even when barely squeezing the nozzle. However, with the original tank I never had a problem there or anywhere else.

Rick, I could probably clamp the old filler neck close to the tank itself with a gas resistant rubber coupling. It just wouldn't be rigid anymore, especially when the nozzle is hanging on it. Also, I think that vent baffle runs the entire length of the tube so it would have to extend past the connection up to the tank.

All I know is it's almost time to fill up again and I'm not looking forward to it.

cutlass47

How can you tell if your gas tank cap is vented or not on my 1972 Cutlass? It just says open slowly on the top of cap and nothing about being vented! Several years ago, after I installed a new gas tank and when I filled up for the first time, there was a strong smell of gas in my enclosed garage until I siphoned out several gallons from the tank. I assumed that the locking ring over the sending unit was not tightened enough, so I have never filled the tank again more than half full. Maybe the real problem is my cap is non-vented. Where is a good source for a quality vented gas cap?

Allan R

If your cap has a double latching system, then it is vented and is correct for 72. If your cap says "Not Vented" you have the wrong one.

Other sources of strong fuel odors:
- overfilled gas tank
- leak in hoses
- kinked, or improperly connected vent lines from the fuel tank
- leak in the gas tank?

I ran into a problem with the vent line on my 72 being too old and it cracked, allowing gas to flow onto the tank and down close to the exhaust.

If you've never changed the fuel hoses or vent hoses, maybe it's time.

Check out page 8-3 of the 1972 Oldsmobile CSM

cutlass47

Allan, the cap only says to open slowly on top and no indication of vented or non-vented. The new gas tank was installed 5 years ago and I bought cap about the same time and only driven about 600 miles since then. At same time, I had all new rubber fuel hoses from gas tank to standpipe installed and new metal fuel lines from front to back installed (except mechanic could not install metal fuel line that has to go over back tire area to gas tank & instead used rubber fuel hose instead. Probably not good idea, but I think body would have to be lifted off frame to install metal fuel line). Tank has only been filled completely when first installed and that was when I siphoned about 1/2 of tank and no longer have strong gas smell in garage. No indication of fuel leak at that time or since then. I will try to find a cap that indicates "vented" and hopefully I can fill up my tank.

Allan R

You are right that the body has to be lifted to put new fuel lines in. But IIRC the OEM cap for 72 does not have any 'vented' stamping on it. I think it just says to open slowly.

Rob delta

Here is a diagram of the filler neck that the Spectra technician emailed to me. He sent this to me weeks ago but I wanted to post it here to clarify things.

DeltaDevil88

I say try the Dorman brand fuel tank

Allan R

Just thinking about this again. When the tank was replaced was it the GM34R you installed? Someone might have ordered the 1970 tank GM34Q by mistake? It's a non vented tank but looks exactly like the 71/72. I know you said the work was done for you by a mech, but I'd take a look under the car and check to see if he didn't just plug some of the vent lines to accommodate the wrong tank?