Dumping Fuel on Track Through Filler Neck - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 23 Old 01-23-2011, 07:30 PM Thread Starter
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Dumping Fuel on Track Through Filler Neck

Several of us with fox bodies and SN95 cars had an issue last summer with dumping fuel while on track at HPDE. We're thinking that the exhaust was getting hot enough to heat up the fuel lines. Fuel then spewed up through the fuel filler neck. If we filled the tank, the problem wasn't as severe until we started to burn a good amount off.

Has anyone had a similar issue? What did you do to correct it?
All of our cars have panhard bars with exhaust dumps along with stock fuel tanks.
We're thinking of doing the following:
1. Side exhaust using same-end inlet and outlet mufflers
2. Wrapping the exhaust with high temp tape
3. Create a shield between the exhaust pipes and fuel lines

Did we miss anything that might help? Maximum Motorsports has been very helpful with these suggestions above.


'90 LX 5.0 - HPDE Car
24 Hrs. of Lemons/Chump Car Series - Grim Reaper Racing '94 Mustang V6
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post #2 of 23 Old 01-23-2011, 11:47 PM
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I've never heard of this. Could it just be your overfilling the tank and when your taking those high speed turns it's coming out? I don't get what the exhaust has to do with heating up the lines and fuel coming out of the filer neck. I've seen guys spewing fuel from the neck and later they told me it was because they overfilled their tanks. Most guys with stock style tanks don't fill them up to the top because of this. I myself keep the tank 1/2 full before every run. More then enough for a 30 min session and less weight.

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post #3 of 23 Old 01-24-2011, 02:15 AM
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This has been nagging me on my '92 for a long time now. Near as I can figure, the problem is the fuel and its vapor heats up and expands so fast the check valve closes when the fuel sloshes, and then the pressure holds it shut. I have done all of the following, to no avail:

Wrapped the tailpipes around the tank with insulating pipe wrap
Relocated the lines above the tailpipes a few inches further away
Wrapped the lines in insulating wrap
Attached sheet aluminum shielding between the tank and the tailpipes
Reversed the spring in the check valve on top of the tank

I now live 10 minutes from Bondurant's facility so I stopped by to ask thier shop chief what they used to do about it when they ran Mustangs. He suggested running the biggest, longest vent line I could muster, and attaching it so it vented out the center under the bumper. He warned me that even then, it would likely piss out the vent, but at least then it wouldn't be next to hot tailpipes.

So I got a rubber stopper and a 90-degree 3/8 elbow and plugged it in the top of the tank I attached something like 10 feet of 3/8 fuel line, coiled on top of the tank and then routed down and secured near the center bottom of the bumper cover. Then I turned the end up vertical and installed a check valve from pegasus Pegasus - Fuel Vent Check Valve, In-Line for 3/8 inch Hose because I just didn't feel right having the vent line unchecked in the event of a rollover.

It works fine as long as temps don't get too high, but when it was 104 at PIR with a track temp of over 135, by the time I was near the end of a 20-minute session, the tank was pressurizing and pissing out the cap again.

Another thing that seems to have helped is I clamped a stand-off to the passenger side tailpipe to keep the pipe from getting shoved right up next to the tank by the tire rubbing against it. Now it's got a minimum 1/2-inch clearance at all times. I'll know if it worked when I get it back to a really warm track day.

Another example: https://forums.corral.net/forums/show....php?t=1094636

Last edited by MFE; 01-24-2011 at 02:17 AM.
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post #4 of 23 Old 01-24-2011, 05:21 AM
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I had a gas cap that did this. I also run tailpipes on my car and it hasn't done this since. YMMV

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post #5 of 23 Old 01-24-2011, 06:37 PM Thread Starter
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thanks for the help. I should have expanded on what the fuel level has been. I usually put about 5 gallons in it per session on top of what's left in it, so I suspect about 7 gallons is in the tank at the beginning of the session. I never fill the tank, but friends have done so I think to get the fuel temps down by mixing the cooler added fuel with the hot fuel in there.

I think you're on to it MFE - a fast build up of vapor pressure under hotter conditions is causing the fuel to be displaced. I'll certainly look into your fixes.

Should I still consider side exhaust and wrapping the pipe?

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24 Hrs. of Lemons/Chump Car Series - Grim Reaper Racing '94 Mustang V6
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post #6 of 23 Old 01-24-2011, 07:09 PM
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Yes, the fuel acts as its own coolant, it seems to get worse as the level gets lower. Side pipes is up to you, I don't think it could hurt, but they can present their own routing problems.
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post #7 of 23 Old 01-24-2011, 07:18 PM
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On my 89 had the same problem. Replaced the vent valve and ran the line out the right fender area and that resolved the issue. My exhaust does dump right after the mufflers in front of the axle. Have not had a tank pressure problem since then.
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post #8 of 23 Old 01-25-2011, 12:05 AM
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I remember reading a thread awhile ago either here or at CC about lots of heat related issues with dumps. I ended up keeping full tailpipes with my PHB and haven't had this issue (of course I did melt the rubber shielding around the fuel lines, even when I wrapped them in heat wrap, in about 20 minutes of track use and had to majorly re-route them to avoid further damage).
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post #9 of 23 Old 01-25-2011, 08:54 AM Thread Starter
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Unfortunately, we all have full length sub frame connectors in our group. One guy notched his and routed the side exhaust through the notch to maintain ground clearance.

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24 Hrs. of Lemons/Chump Car Series - Grim Reaper Racing '94 Mustang V6
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post #10 of 23 Old 01-25-2011, 01:25 PM
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Anyone with a 98-04 have these problems? The fuel lines are routed differently on the newer models.

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post #11 of 23 Old 01-25-2011, 07:48 PM
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I have this issue but it comes out of the vent tube when the tank is 3/4 or more full. The car has side exhaust and a Fuel Safe cell with rollover valve in the vent. I put a "baffle" in the vent hose with a few small holes poked in it and it seemed to work a little better but I haven't been able to fix it 100%.

Sean
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post #12 of 23 Old 01-26-2011, 04:04 PM
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Prime example of problem with Tone's car:


Basically, You need a flapper valve.
Fuel in a non-baffled stock tank sloshes up the filler tube and vents out the gas cap.

You can try like Sean did, to put a baffle in the tube (slow down the sloshing).

I battled this dilema for years, until I finally fixed it the a flapper valve in the fuel cell
http://www.dariusrudis.com/junk/fuel_cell.jpg

Darius Rudis

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post #13 of 23 Old 02-05-2011, 02:00 PM
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I go the cheapie route and JB Weld up the vent holes in the cap. It's worked for me and I've seen no ill effects.

Justin
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post #14 of 23 Old 03-22-2011, 09:19 PM
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Only happens on my 94 GT with low fuel level. Fill it up and it's fine (so far).

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post #15 of 23 Old 03-23-2011, 11:09 AM
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never had this exact issue, but something similar. i got a ton of pressure coming out of my cap when opening it and if i opened the cap fast, gas would spill out. like it was trapped in the vent tube by the pressure in the tank. turned out, the purge soleniod that goes to the charcoal canister, was stuck closed. got a new one and all was good again. possibly your issue as well?

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post #16 of 23 Old 03-31-2011, 08:48 PM Thread Starter
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Quote:
Originally Posted by mustang-madness View Post
never had this exact issue, but something similar. i got a ton of pressure coming out of my cap when opening it and if i opened the cap fast, gas would spill out. like it was trapped in the vent tube by the pressure in the tank. turned out, the purge soleniod that goes to the charcoal canister, was stuck closed. got a new one and all was good again. possibly your issue as well?
I'll look into this, but I think there's more to it since heat constantly builds up during my sessions on track.

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post #17 of 23 Old 04-04-2011, 10:39 PM
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This happened to me when I ran my solo Mustang in a Solo I a bunch of years ago. About once a session the tank would pressurize and blow fuel past the cap. We found a blocked tank vent and once we cleared it the problem went away.

I guess this could be heat related but I have not had any issues with my RX7 race car and I am certain that it generates way more exhaust heat than a mustang. The RX7 has an ATL cell and the vent is 3/8" hose with a clear fuel filter on the end (to keep the dirt out). The vent hose is about 18" long.

If the tank is venting properly it cannot build pressure and as long as the cap seals the tank there should be no spillage.

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post #18 of 23 Old 06-10-2011, 10:26 PM Thread Starter
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Update from an HPDE last weekend at VIR Full Course.

3 of us have converted our fox bodies to side exhaust. None of the cars experienced the dumping issue and ambient temps were around 93 degrees.

1 car in our group is an SN95 still with the dumps - he was black flagged for the fuel dumping issue.

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post #19 of 23 Old 06-10-2011, 11:28 PM
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Quote:
Originally Posted by PaulMan View Post
Update from an HPDE last weekend at VIR Full Course.

3 of us have converted our fox bodies to side exhaust. None of the cars experienced the dumping issue and ambient temps were around 93 degrees.

1 car in our group is an SN95 still with the dumps - he was black flagged for the fuel dumping issue.
Happened to me again at Sebring over Memorial day Weekend with Track Guys, inc as you can see in the pic below. This only happens when my tank is at 1/4 or less....


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post #20 of 23 Old 06-11-2011, 08:01 AM Thread Starter
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A couple of things that will help even more would be to improve the venting of the tank and to also start a session with at least a half tank of gas. As the gas level lowers the tank's vapor pressures get worse since the vapor and heat can't be released fast enough - this along with hotter fuel return temps from the rails in the engine bay are both causing the gas to be pushed out.

I also added some gas between sessions. Mixing cooler gas from cans I brought helped. Having more volume of liquid than vapor in the tank long enough for a session got me by.

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post #21 of 23 Old 11-19-2015, 11:56 AM
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Reviving this thread because I think I cured it, and in my case, it was the pump. https://forums.corral.net/forums/16477394-post10.html
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post #22 of 23 Old 11-20-2015, 12:20 PM
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You know, funny you should mention that, my fuel spilling issues started on a very hot day after I went to Aeromotive 340 lph pump. Before this, no matter how hot it would get, I would never have any issues with gas spilling. Another thing that's worth mentioning is that I've done a couple of track days since that issue, and didn't have any fuel spill issues. The two things that were different were the cooler temperature (90 degrees vs 110 degree), and different track that's just as technical but slower (Streets of Willow vs Buttonwillow). The question for me now is, will the stock 155 lph pump support my motor.

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post #23 of 23 Old 11-21-2015, 05:55 PM
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FWIW, years ago I remember a discussion where the question was whether a large pump - not necessary for the motor's current needs, but only added for future upgrades - heated the fuel due to unnecessary volume/re-circulation. At that time the consensus was yes the fuel would be heated but there was never any empirical evidence in support. Perhaps we now have some support for the too big pump heating fuel theory.
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