Fuel backing up in the tanks

I have an older CAV/GTD 40 and when I leave the car out in the sun the right side fuel tank backs up and leaks into the cockpit. I have installed check valves in the L&R fuel line at the pumps, but this doesn't seem to be working. Any ideas?
 
Sounds like you need vents in the front and rear of the tanks. I bet you are parked on a hill facing down the hill aren't you??The heat is making the air in the tanks hot which expands and pushes the fuel up the filler tube. You will have to put rollover valves in them as well for when you get upside down or when you get parked on a hill. It will keep the tanks from overflowing. Do a search on the forum for vent lines. There should be several threads about it.

Bill
 
Hi Tony
Maybe have a chat with Mick Sollis at Southern GT in the UK as one of his customers had a similar problem with his car after fitting it with an injection system, and I think Mick has been involved in the rectification work.
 
Similar issue with the last "early" CAV 40; Has vent lines vented into the air filter housing, (got it through Califonia emissions as it was assembled in that state). On hot days with full tanks will expand up the lines and bleed into the air filter housing and run into the carb air horn. Just filling the tanks to where the pump nozzel first clicks "off" seem to work. Just don't top them off. I don't plan on rolling over so I didn't think of the one way valves to install yet. If I roll it over and live, my wife said she will kill me for wrecking it anyway!!!
 
What you guys are describing is exaactly what I am telling you is the problem. With out the roll over valves it will continue. The rollover valves will close in the upright position when fluid rises in the tube, preventing it from going into the air filter or out the vent line and into the interior of your car. You must add vent lines from the rear and the front of both tanks. Then when parked on a hill, say nose down. the rear of the tank will have an air bubble in it. As it get heated It will expand and go out the rear vent line to atmosphere. If you just have one vent line, say in the front of the tank, then given the scenario above it will push the fluid up the line to the rollover valve, which will then close, and then you will begin to pressurize your fuel tank and you will hear a hiss if you open the fuel filler cap, and you may get a face full of gasoline as well. Venting to the air filter is the wrong plce for a single vent line to go. If the fuel rises enough to flow out the line the fuel will go one of several ways. One is all over the top of the engine(not good), down the ports and sit in the cylinders or just on top of the intake valves. A disaster either way. Gasoline in the oil pan, flooded cylinders or worse a big boom!!!! These vents must be put in properly or you will just compound your problem. See my post http://www.gt40s.com/forum/gt40-build-logs/13742-drb-5-a-5.html down about the middle of the page. It has how I did it. I have no gasoline smells or spills. Guess how I figured this all out??????

Bill
 

Seymour Snerd

Lifetime Supporter
With out the roll over valves it [fuel overflow] will continue. The rollover valves will close in the upright position when fluid rises in the tube, preventing it from going into the air filter or out the vent line and into the interior of your car.

Bill -- did you mean to say "The rollover valves wil open in the upright position..."? I'm assuming you are using rollover valves the way one would expect, that is, when rolled over they close.
 

Michael Holmes

Lifetime Supporter
I had this problem but it was caused by having both tank pit cocks open at once. The fuel pump no only pumped fuel to the carb but also to the other tank until it was full and overflowing via the vent and into the car's cabin.

Make sure only one tank is open at a time.
 
Alan,
Yes that is what I meant. The rollover valves are a part of the VENT system. They will allow air to move in and out as the fuel level changes as long as it isn't done rapidly. This keeps the tanks from pressurizing. The little ball in the valves will be pushed up as fluid rises in the tube eventually closing and causing back pressure(single vent scenario where the vent line isn't in the air bubble).
You can take one of these valves and hold it in your mouth and you can breathe in and out through the upright valve. But try to blow forcefully and it will shut.
The dual vent(per tank) setup is done with 1.) each line vented to air. They have to be high enough to allow fuel to run up the tube but not up to the rollover valve itself(slight overfilling of the tank is an example). Probably up to the level of the rear window or the sill in the front, in front of the windscreen. This is very expensive in that the roll over valves I found were not cheap. It would require 4 of them. 2.) Front and rear vent lines are joined above the level of the tanks near the top of the line and have one line for each side(what I have).
P9060282.jpg
I guess there could be a third way where if you didn't mind running lines all over the car and terminate them all into the bottom of a "catch can" and using one rollover valve vented to air. A bit much I would think.

Micheal,
I didn't like the idea of having a lot of switches and mechanical valves to worry about. I am easily distracted and would wonder why the engine quit all of a sudden. Just more to go wrong(as you found out with your incident. I use one set of pumps, return line to the tank without the pumps and a link between the two tanks with a one way valve toward the pumped tank. The principle here is that the non pumped tank will flow back to the pumped tank when its volume is higher than that the pumped tank. If the return flow is faster than the connected line, the non pumped tank will fill til the rollover valve closes, and then fuel will be forced to the pumped tank(this would only happen if the linked tube is so small that flow to the pumped tank is very slow. I chose a large line and this has never happened.
PA270338.jpg
What I do see is a small difference in the fuel level gauge(in the pumped tank). When running the level will be a little lower than when it is shut off. The only inconvenience here is that my low level warning lite will come on a little sooner than it should, which isn't really a bad thing. There is really a lot more to it in my car, but the principle is the idea here. If you want to know more, take a look at my build thread DRB #5 or PM me and I'll talk you through it.
If and when I get my car on the road(should be any day now if nothing else goes wrong) and have had a little fun with it, I plan to modify this setup in my car to be a little more complete and rule out any "possible" short comings of my system. It will involve pickups from both tanks and returns to both tanks with trap doors in both around the pickups and the ability to fill both tanks from one filler pipe.

Bill
 

Seymour Snerd

Lifetime Supporter
This is very expensive in that the roll over valves I found were not cheap. It would require 4 of them.

Bill -- from your picture it looks like the red thing is an ATL (UK) TF-AF-009 8 mm Tank Vent Valve for 45 GBP each(?) If so, is that also providing the rollover drain blockage, or is that done in some other part of the assembly?

I ask only because on the Demon site Fuel Tank Vent Valves | Fuel System | Motorsport Shop | Demon Tweeks
that particular part is not identified as having a "rollover valve, float balls" feature, while the one next to it which looks different is described as having a rollover valve feature.

Or maybe the easier question is: what exact parts did you use?
 
Interesting thread. I have thought about adding vents on the rear of my tanks after an incident that I had. One day my heater hose blew off and sent hot coolant all over the passenger side of my car. Fortunately no one was sitting there to get covered with hot coolant. I did not have time to deal with soaking up all the coolant so I threw a jack under the car and raised the rear so at least all the coolant would stay at the front of the footwell and then turned up the heater in my garage to warm it up and help dry it out.

I got a call few hours later from my wife that the whole house smelled of gas. The tanks were full and the only vent was on the front. The garage warmed up a good 20 degrees and the fuel expanded and a lot of gas/vapor came out the vents. I had roll over valves but I don't believe they will stop a slow seep when the car is upright.

This could have ended badly. I have a gas hot water heater in the garage.
 

Seymour Snerd

Lifetime Supporter
Interesting thread. I have thought about adding vents on the rear of my tanks after an incident that I had.

Yes, Bill's key insight, that a long skinny tank has two potential air spaces, and thus requires two vent locations, is something that hadn't occurred to me. Superformance tanks, for example, have no provision for venting the rear, so any time they are near full and pointed downhill there's the potential for an "eruption." So this goes on my list of SPF fuel tank issues.
 
Hi Alan,

Nice to see you at cars and coffee Irvine a few weeks ago.
Remember the green eggs and ham at breakfast.
Now you have me thinking.
On my Cav at the back of each tank I have a fuel pickup and a vent.
Both vents are capped and have been since it was built.
I never had any fuel smell problems or "sploshions" as ricky would say.

Do you think I should vent these two capped lines.

If so where do I vent hem to?

Thanks, Eric
 
For some info on the roll over valves see Martin's build thread http://MDA Mk1 with Gulf Arches - Martin P on page 17 post #334. It tells how the valvles work to keep fluid in and allow the air to move in and out. There also is a thread by some of the SPF guys on the need for carcoal canisters and/or sealing the system and how it should be routed. I think it is the one on gas smells in the garage. Worth checking out.

Bill
 

Seymour Snerd

Lifetime Supporter
Nice to see you at cars and coffee Irvine a few weeks ago.
Remember the green eggs and ham at breakfast.
Now you have me thinking.
On my Cav at the back of each tank I have a fuel pickup and a vent.
Both vents are capped and have been since it was built.
I never had any fuel smell problems or "sploshions" as ricky would say.

Do you think I should vent these two capped lines.

If so where do I vent hem to?

Hi Eric -- I love being introduced to good restaurants I would never walk into on my own. That was fun!

Re the tank vents: I defer to Bill Musarra on this subject, although of course the old "if it ain't broke don't fix it" concept always applies.

In my case, since my car isn't even running yet I'm kind of operating on theory. As Bill says above you want to vent them as high as possible, so what I'm thinking about for mine is running a line up the firewall to under the lower corners of the rear window (I have vents at the front via the filler cap so it's only the rear I need to deal with). l'd love to figure out a way to vent "away from" the body but that part of the car is covered with scoops leading back into the engine room. Possibly a small puncture in the rear-clip to firewall gasket; maybe just exterior to the door gasket at the upper rear corner. I need to think about that some more....

This has been a hot topic for Superformance cars for a long time though. Don't know why the user experience would be different between the two, although of course not all SPF owners have the problem either. There are of course other differences in the tank systems. The SPFs have a locking gas cap with a particularly unpredictable vent opening so that complicates the issue.
 
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Seymour Snerd

Lifetime Supporter
For some info on the roll over valves see Martin's build thread http://MDA Mk1 with Gulf Arches - Martin P on page 17 post #334. It tells how the valvles work to keep fluid in and allow the air to move in and out. There also is a thread by some of the SPF guys on the need for carcoal canisters and/or sealing the system and how it should be routed. I think it is the one on gas smells in the garage. Worth checking out.

Bill

Bill -- thanks!

Here's a pointer directly to that post: http://www.gt40s.com/forum/325798-post334.html

The most recent of the Superformance threads is this one http://www.gt40s.com/forum/superformance-gt40s/32832-fuel-smell-garage.html although it gets a bit circular since I just updated that thread after reading Bill's comments above along with Johnathan's rather exciting story.
 
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