Gas leak -- very puzzling

[Laurent Gauthier]

Hello,

Last weekend I took my car out and some stuff happened that left me scratching my head as I can't figure out what is going on. I thought maybe someone here might have an idea that could help me.

Basically as I was driving back to my garage the engine could not hold idling at all, it was almost as if my tank was getting empty and gas was flowing sporadically to the engine. At the same time I had filled the tanks in the morning so I did not believe I would have used it all. At the same time, my gauge was not working properly (it was showing full).

I managed to get the car to the garage. There, as I stepped out I realized a pretty significant pool of gas was forming near the right front wheel (4-5 feet diameter). There was also a line of gas coming from the street. Needless to say, I was happy nobody threw a cigarette there.

The time it took me to locate something to syphon the reservoir that leak stopped, and as I opened the right tank I realized that (1) it was still full (2) it was under pressure (went 'pshhhhht' when I opened it) (3) the leak was in fact gas that had come out of the opening and dropped into the overfill.

Then I checked the left tank and it seemed pretty empty. I think (but I am not sure) that after I had opened both tanks they balanced out (the level in right one dropped).


The problem for me is that in order to get this fixed I have to drive out of the city and I don't want to take that risk without understanding what's going on.

Thank you in advance for your ideas & help

Laurent

 

[Daryl Adams]

Yikes!! Could it be a clogged fuel vent? Are you running fuel injection?

 

[Ian Anderson]

2 Possibilities that I can think of

If you are running injection the return is going to the incorrect tank / your cross over valve is not working

Now when you say your gauge was not working this could also point to a problem in your cross over valve wiring as running 1 gauge the gauge "swaps" over with the tank selected normally on a double pole double throw switch

Perhaps the wiring is wrong and with the selector in the middle (or off) position on a 3 way switch (Left Off Right) it is still activating a pump and gauge (It did on mine)



If you are running carbs
When pumping out of one tank and the other tank's pump is turned off there is flow backwards through the pump to the incorrect tank In this case fitting non return valves will cure it
Do not rely on the non return valve biult into the pump they do fail.

Now when you say your gauge was not working this could also point to a problem in your cross over valve wiring as running 1 gauge the gauge "swaps" over with the tank selected normally on a double pole double throw switch


Ian

 

[Steve C]

Laurent,

As shipped from the factory (don't know how your engine install might have changed this):

R & L tanks are connected by an open cross connect line at rear lowest point of ea tank (check to make sure this line isn't crimped/crushed not allowing equilazation between tanks as designed or could be blocked due to debris but, unlikely as this is a large diameter line).

Gas gauge ONLY in right tank so only shows rt tank level.

Fuel supply to engine is from left tank only.

There is a fuel return fitting to left tank only (used as return line for FI installs or in my case return for swirl tank set up that insures my carbed engine always has supply of fuel even if fuel in the longitudinal tanks is low and car in a nose down attitude)

Gas cap assys have a vent/overpressure relief and overflow drain line Are you using factory gas caps or something else?). Per you post above the overpressure feature is working but, the vent feature might not be.

Suspect you filled up early with cold gas, during day fuel warmed up, something clogged in or cross connect line crimped not allowing equalization between tanks and or vent problem with right tank gas cap so you were demanding only from the left tank all day and empied it while right tank volume expanded and overflowed.

Make sense?

Gives you some things to check (Fuel cross connect line, rt tank gas cap/fuel fill assy and while you're at it check your fuel filter to see if FUD is or will clogg you up.

Steve P2125

 

[DaveM]

Do you have fuel injection? Likely cause is return line only goes to the right tank. There is a crossover line between the tanks, but it may not match the flow of a high pressure fuel pump. If you have a carb I would suspect blockage in the crossover line or at your fuel filter. If you need to drive the car to a repair shop I would siphon out a third to half the gas so it doesn't overflow.

 

[Laurent Gauthier]

Thanks a lot for your input on this -- and yes, I am running fuel injection (forgot to mention it in my initial post)

To echo on DaveM's point, did anybody have to change the size of the cross-over line because they used injection?

Of course, it would help if I knew how the lines have been set up, but my builder is hard to reach and I can't easily crawl underneath the car!

 

[Rick S.]

If each tank has a vent line for filling, and one was plugged up, would fuel return to that tank push fuel out of the vent line on the other tank?

 

[Steve C]

Laurent,

Read my post above again.

I believe the only return is on the left tank (at least on mine that is the case).

Easy to see what's going on if you remove the covers left and right of engine that give access to the rear of the fuel tanks (with left cover open will allow you to see plumbing out of and into the tank and fuel pump routing, right cover open allows you to remove battery and battery box and see plumbing to right tank).

I doubt the fuel pump return is plummbed to the right tank as I don't believe there is a high return nipple there.

With a flashlight and mirror you should easily be able to see the tank crossover line; it comes out inboard of rear of ea tank then goes forward and crosses from one side to the other almost to bottom of the belly pan...It might be crushed or kinked if car was incorrectly picked up or during engine install was hit. Or recent work was done and was crimped.

Is this a new occurrance? Have you driven the car enough to deplete the left tank prior to this fill up and needed to rely on the fuel load in the right tank .In other words were you using only part of the left tank ea ride prior to filling up again? Have you always filled both tanks equally? Has the gauge (only connected to the right tank) ever moved off of full (if so this is a new occurance and could be related to crimped crossover, gas cap vent, or crud clogging the crossover line).

Steve P2125



SteveP2125

 

[Jack Houpe]

Laurent, I had a similar problem in the beginning, when I took off the cap it was under pressure, I believe this was because of expansion due to the fuel heating up while under pressure of the fuel injection thus creating pressure over a period of time. My fix right or wrong was to take the rubber seals off the gas cap that has the key in it. Problem solved. As far tank equalization if the tanks are vented then the cross over line should keep up with the usage as long as the pump and pressure bypass are on the same tank. When I fill my tanks the right side seems to have 1-2 gallons more than the left, but if it sits it will equalize.

 

[Laurent Gauthier]

Jack, when you say you had the same problem, do you mean that there was some pressure in the tank, or that there was pressure in the tank + felt like running on an empty tank + large gas spill?
Thank you

 

[Jack Houpe]

Laurent, I had excessive pressure in the main fuel tanks (the ones we fill up). My system may be different from yours, I have a catch tank (small 3/4 gallon tank) which a low pressure high volume pump feeds, then then high pressure pump for the EFI pulls from the bottom of that small tank and feeds the EFI, also the return from the fuel pressure regulator feeds that small tank, the over flow from the little tank goes into the left side main tank. By removing the rubber seals on the gas caps relieved all the pressure thus preventing the main fuel tank cross over from being pressurized. If you have any questions please feel free to PM me and I will give you my phone number. Here are some photos of the tank and the system I have.

 

[Steve C]

Laurent,

See pics of my install below:

Like Jack I have a catch can (swirl pot) atrangement as I described in post above.

Low pressure HV pump in the left sponsoon pulls fuel out of the left tank through the Canton large filter in pic then into the swirl pot. Pumps on the firewall (can select either pump, have 2 to insure have a back-up) take suction on the swirl pot and supply the carb.

Overflow of the swirl pot (there is always an overflow as the engine demands less volume that the sponsoon pump puts out) goes back into the high return into the left tank and the full swirl pot insures that the engine pump chosen always has fuel available even if the main tanks are low on fuel and car in a down by nose attitude when without the swirlpot the pumps would starve.

Right and left tank equilize through the right to left tank cross connect connecting the lower rear of both tanks.

Although I can fill from only one side (if I allow for a slow fill that the equilizer line can accomodate AND have the opposite cap open to insure a good vent) I perfer to fill 50/50 ie 1/2 load into rt tank the 1/2 load to left as it allows faster fueling.

Never have had the problems you describe now many fill ups and 2,500+ miles.

As you describe assuming your supply and return is to the left tank you must have run that tank dry with out knowing as the fuel gauge is in the right tank and there must either be something preventing flow through the crossconnect line right tank to left (a blockage) or a vacume due to bad gas cap/vent causing a vacume on the right tank that kept that tank full allowing it to warm up during the day and expand to the point that it overpressured and overflowed.

Assuming you have driven the car through a few fill ups has something changed or been changed or have you never run far enough to let the left tank (approx 10 gallons) run dry as it seemingly has in this case. Do you always fill the left tank (if so could always have had this problem and not known) and have you never filled fully up and in climate that would have let change in ambient caused gas in right tank to expand and overflow (in other words you might have had this all along and not noticed and in that case really could be something clogging or a crimp in the crossover line not allowing tanks to equilize.

I still say it's either clogged cross connect or vacume lock.

Let us know.

Regards, Steve P2125

 

[mike]

Laurent,

See pics of my install below:

Like Jack I have a catch can (swirl pot) atrangement as I described in post above.

Low pressure HV pump in the left sponsoon pulls fuel out of the left tank through the Canton large filter in pic then into the swirl pot. Pumps on the firewall (can select either pump, have 2 to insure have a back-up) take suction on the swirl pot and supply the carb.

Overflow of the swirl pot (there is always an overflow as the engine demands less volume that the sponsoon pump puts out) goes back into the high return into the left tank and the full swirl pot insures that the engine pump chosen always has fuel available even if the main tanks are low on fuel and car in a down by nose attitude when without the swirlpot the pumps would starve.

Right and left tank equilize through the right to left tank cross connect connecting the lower rear of both tanks.

Although I can fill from only one side (if I allow for a slow fill that the equilizer line can accomodate AND have the opposite cap open to insure a good vent) I perfer to fill 50/50 ie 1/2 load into rt tank the 1/2 load to left as it allows faster fueling.

Never have had the problems you describe now many fill ups and 2,500+ miles.

As you describe assuming your supply and return is to the left tank you must have run that tank dry with out knowing as the fuel gauge is in the right tank and there must either be something preventing flow through the crossconnect line right tank to left (a blockage) or a vacume due to bad gas cap/vent causing a vacume on the right tank that kept that tank full allowing it to warm up during the day and expand to the point that it overpressured and overflowed.

Assuming you have driven the car through a few fill ups has something changed or been changed or have you never run far enough to let the left tank (approx 10 gallons) run dry as it seemingly has in this case. Do you always fill the left tank (if so could always have had this problem and not known) and have you never filled fully up and in climate that would have let change in ambient caused gas in right tank to expand and overflow (in other words you might have had this all along and not noticed and in that case really could be something clogging or a crimp in the crossover line not allowing tanks to equilize.

I still say it's either clogged cross connect or vacume lock.

Let us know.

Regards, Steve P2125

i looked at my tanks and they are baffled pretty good. i really wouldnt think starvation should be an issue.

 

[Richard]

Laurent, as your car is only one number off from mine I would expect our cars have the same fuel system. As Steve stated the rear of the left tank has three connections. The large one at the bottom is the cross connect that runs to the right tank and that is the only connection at the rear of that tank. You can see most of that line as it comes out of the left sponson just below the motor mount, then runs up just in front of the engine and back down and into the bottom of the right sponson again just below the motor mount.
The next line out of the bottom of the left tank is the fuel supply line. It supplies the fuel to the carbs and/or injectors. The final connection comes out near the top of the tank and is the FI return line. All old news I know but as I just pulled the tanks out of my car and I might have some additional information which may help the discussion.


At the front of both tanks there are three connections, the first one is the filler neck but the other two have to be vents. I haven’t had a chance to look inside the tanks yet but I would guess one vents the front and the other vents the rear of the tank. Also of interest is the fact there is a flapper valve about 6” up from the tanks in the filler necks. I suspect in your case that your flapper may be stuck in the closed position, OMG hope that doesn’t hurt, lol. (see photo). The vent lines come up off the front of the tank and go to the top of the filler necks. The one other line in the area is an overflow line that has a hole next to the filler cap and dumps out on the ground.

If your flapper valve is closed surges from the tank either coming up from the filler neck or vent lines would not easily return to the tank. Your left tank may have had the same amount of fuel as the right tank but the filler neck was full from the flapper valve up to the gas cap.

The other thing is since the gas gauge sender is in the middle of the right tank it shouldn’t have shown full. The connection to the sender is just under the oval opening on the top of the sponson in the middle of the door opening so if you’re still having problems you should pull the plate and make sure the wires are still connected. The pictures say it better.

I did find some welding slag in the tanks which is why some of you have had to replace many fuel filters. Also the cad platting on the filler necks does not seem to be of the highest quality as seen by the metal particulates in the vent hoses.

 

[Steve C]

Hi Rich,

I don't think his problem is the flappers (check valves) as they are metal to metal contact not air tight seal used only to prevent heavy sloshing of fuel foreward due to longitudinal tank construction when heavy braking. Also the flapper is top hinged with its mass pulled down by gravity so unlikely stuck anyway (easily checked if he has filled up into the right tank or if he does and the fuel easily flows in).

Vent lines primary purpose is for fueling to insure no air trapped during fueling that would preclude a full tank (note they are UNDER the gas caps).

The gas caps should have a vent feature that allows the tank to not collapse under vacume caused during fuel consumption and during fuel temp change and the cap should also have an overpressure feature for opposite condition (the overpressure feature seems to be working in Laurent's case). Has he changed the caps?

We need more info from Laurent as I questioned in one of my posts above: Is this a new condition, has he filled up both tanks in past without a problem, how far does he go between fill ups, does he only fill the left tank and the refill that tank after he consumes less than the 10 or so gallons it holds and this time did he go further than the left tank would take him causing the fuel starvation he noted cuz the right tank isn't supplying through the crossover, has he ever seen the gas gauge show less than full when he fills up cuz the right tank has never been able to supply through the crossover line, no problems in past and now....if so something is different and we need to know what.

I still think it's either crossover line not allowing equilazation or something wrong with his gas cap vent or both.

Steve P2125

PS...Laurent...Give us more details of your plumbing and specifics as requested and someone might have better answers.

 

[Steve C]

Laurent,

I just re read your original post.

If as you stated "after I had opened both tanks they balanced out (the level in right one dropped" I would also assume you can see the fuel gauge has dropped from a full reading (please confirm).

So if in fact you fueled up in the morning and topped off, ran about 100 miles or so (10 gallons in left tank at 10 miles/gallon = empty)and then noticed the engine seeming to starve it would seem you consumed most if not all of the left tank and were not getting any of the fuel from the right.

As I stated above causes could be plugged crossover line OR the right gas cap not venting and causing a vapor lock on the right tank. If when you opened the right gas cap you heard a sucking sound it would confirm this but, if the tanks equalized after you opened both caps it's likely the cap.

As supplied SPF supplies locking gas caps that have a vent and overpressure feature (there are two drilled holes opposite each other through outside edge of the cap that run over the rubber seal and by means of the vent spring valve in the center of the cap allow breathing if a vacume is pulled on the tank or pressure relief if needed. Has someone messed with your caps, do you have different caps?

If a cap issue is the cause and not a clogged bypass, that upon further understanding doesn't seem to be the case, then an easy fix if using the original caps and they are defective is to do what Jack suggested above (remove the cap gaskets) but, you will get fuel fumes in the garage so best to try to get cap issue corrected or new caps that work.

Let us know the final verdict.

Steve

 

[Jack Houpe]

Laurent,

I just re read your original post.

If as you stated "after I had opened both tanks they balanced out (the level in right one dropped" I would also assume you can see the fuel gauge has dropped from a full reading (please confirm).

So if in fact you fueled up in the morning and topped off, ran about 100 miles or so (10 gallons in left tank at 10 miles/gallon = empty)and then noticed the engine seeming to starve it would seem you consumed most if not all of the left tank and were not getting any of the fuel from the right.

As I stated above causes could be plugged crossover line OR the right gas cap not venting and causing a vapor lock on the right tank. If when you opened the right gas cap you heard a sucking sound it would confirm this but, if the tanks equalized after you opened both caps it's likely the cap.

As supplied SPF supplies locking gas caps that have a vent and overpressure feature (there are two drilled holes opposite each other through outside edge of the cap that run over the rubber seal and by means of the vent spring valve in the center of the cap allow breathing if a vacume is pulled on the tank or pressure relief if needed. Has someone messed with your caps, do you have different caps?

If a cap issue is the cause and not a clogged bypass, that upon further understanding doesn't seem to be the case, then an easy fix if using the original caps and they are defective is to do what Jack suggested above (remove the cap gaskets) but, you will get fuel fumes in the garage so best to try to get cap issue corrected or new caps that work.

Let us know the final verdict.

Steve

I agree with this, I really don't like the locking caps, I don't live in an area that stealing gas is an issue and sure wouldn't leave my car in a place that I would have to worry about it. If anyone has found a replacement cap please advise. The spring pressure is so excessive I don't think it would vent till several pounds of pressure. The tank needs a vent or a vacuum pulled on it like the new EFI systems in order to work properly. The problem he is having is like vapor lock due to the pressure. Without the addition of a vacuum canister and charcoal filter system he will have to just remove the gaskets on the caps or put a T in the over flow line and tie back into the filler neck tank vent line.

I would like to make note that Dennis Olthoff has a fuel cell now available now, they are safer and I believe plumbed correctly. The cross over line on the new fuel cell is about 1.25 inch, which is a big improvement over the small 5/8 line there now.

Mike, if you looked closely at the tanks and the fuel exits with the car properly set up, (correct front to back level) you will find that there is almost 5 gallons of fuel left between the two tanks that is unusable. I have filled my tanks with gas cans then let my fuel pump, pump them dry to adjust the fuel level sender and found that on level ground I had almost 5 gallons short. I just finished the Big Bend Open Road Race where you travel 118 miles at very high speeds. Without the catch tank I can assure you that some of the long down hill sweepers would have starved the engine when under load.

 

[Jim Cowden]

Yes read all of that but unless I have missed it in the posts you should be looking if the charcoal canister is working.

I presume they have canisters as they would not pass emissions.
The canister takes the vapor from the tank (it is also vents positive pressure) and passes into the canister then the manifold vacuum pulls it into the engine and burns the hydrocarbons.

The fuel cap will not vent outward(it is e legal) ,the cap will only draw air into the tank as the fuel pump can generate negative pressure and crush the fuel tank, fuel cools in the evening or cold weather the tank will generate a negative pressure and also draw in through the cap.

Only positive will go into the canister.
As the supply and returns are in the L/H tank ( stated steve C) the fuel will be hotter in that tank and if it cant vent it will push it over to the R/H and would explain the full tank and overflowing.
Does the tank have vents on L & R tanks to the canister if not this will cause a problem if both tanks are full and they do not vent to each other or the canister (it will not vent through the cross over pipe)

If the pressure increases in the tank by 2psi it will change mixtures.5-10 psi it may cause the idle problems especially if you release the pressure did the engine then idle ok?.

Jack seems to have the same problem with the tank not venting then their is something wrong in that area anyway.
I put my vent hose's to the canister in the filler necks well above the fuel level.

This might help or it might not be your issue.
Good luck

Jim

 

[Steve C]

Jim,

No cannisters on the SPF cars....All pre emmission design.

Jack,

I'm running the original locking gas caps as supplied by SPF w/o problem but, as I noted above the caps have 2 holes drilled through the outer edges and the drill that made those holes also grooved out the metal above the rubber gasket allowing an air passage even if the cap is installed from outside the cap to the vent valve/spring assembly.

Do your caps have these drilled passages? Wonder if they came from the factory like that or Olthoff did a mod?

As I have said before I don't see Laurent's vacume issue nor do I have the pressure issue you had before you removed the gaskets.

Any other SPF owners see either of these issues?

Steve P2125

 

[Jim Cowden]

Laurent, as your car is only one number

At the front of both tanks there are three connections, the first one is the filler neck but the other two have to be vents. I haven’t had a chance to look inside the tanks yet but I would guess one vents the front and the other vents the rear of the tank.