I got a new gas cap. The old one leaked fuel when I mashed the pedal and the gas sloshed backward, it wasn't sealing properly.

Now after driving the car I hear what sounds softly like a kettle. I open the gas kap and the built up pressure escapes and the noise is gone.

My Flowmaster transverse muffler is cooking the fuel inthe tank!! This is a little concerning does anyone have a similar experience and how worried should I be about the boiling gas in the tank. Could it explode?

No problem. Have the hazmat truck follow you.

You might want to put a insulation pad between the muffler and tank.

No problem. Have the hazmat truck follow you.

You might want to put a insulation pad between the muffler and tank.


Yeah:yes: I was thinking more like Fire Department. Would dynamat work or is that more for interiors. I wonder what type of heat barrier would work. There is a heat shield on the muffler but it obviously needs more

I have even considered going with duals and tossing the transverse. I do like the ground clearance though.

Do you have turn downs? Your tank may be letting air in but not letting air escape. As the tank heats up it needs room to expend. Vented caps will only let atmospheric pressure in the tank to replace burnt fuel.

Do you have turn downs? Your tank may be letting air in but not letting air escape. As the tank heats up it needs room to expend. Vented caps will only let atmospheric pressure in the tank to replace burnt fuel.



It's definately not letting air escape. Turndowns?? I'm not quite sure what you are reffering to.

John, your cap is working perfectly. 69 caps let air in, not out. So they whoose when opened. Relax. But cooling your tank is always a good thing. And hearing a leak before the cap is removed is not good. It shouldn't make a sound.
Another thing; always open the cap before cracking open the fuel system. Don't ask.

John, your cap is working perfectly. 69 caps let air in, not out. So they whoose when opened. Relax. But cooling your tank is always a good thing. And hearing a leak before the cap is removed is not good. It shouldn't make a sound.
Another thing; always open the cap before cracking open the fuel system. Don't ask.


I thought the cap was good, its brand new. The old cap didn't seal and was letting out the fumes into the garage. But now after a drive when everything is hot and under pressure the gas can be heard bubbling away, its a little un-nerving. After I open the cap to relieve the pressure it stops percolating.

And you are sure it is a vented cap right? If you create a vacuum (non-vented cap) in the tank, you lower the boiling point of a liquid.

alan

Are you running full exhaust or do your mufflers have turn downs to keep the exhaust off the tank?

And you are sure it is a vented cap right? If you create a vacuum (non-vented cap) in the tank, you lower the boiling point of a liquid.

alan

Fred says the vented caps are suposed to let air in not out. There is definately pressure in the tank that relieves itself when the cap is removed. I suppose the higher pressure in the tank lowers the boiling piont

Are you running full exhaust or do your mufflers have turn downs to keep the exhaust off the tank?

I thought you were referring to the exhaust but wasn't sure. My exhaust exits the rear. If you look on my name and check out my profile I think you can see the tips in the picture of my car. The transverse muffler mounts sideways between the rear diff and the gas tank and I guess it gets hot enough to expand the vapours in the tank and boil the gas.

Shoot the tank, next to the muffler, with a temperature gun to see how hot it is getting to 'percolate' the fuel.

As said, the tank will get warm due to the exhaust, engine heat, trans heat, and road heat, if ambient temp warrants it.

Well, actually, increasing pressure increases the boiling point. Decreasing pressure lowers the BP, that's why it takes longer to cook food in the Rockies compared to Santa Monica. If you have a non vented cap and you develop a vacuum in the tank due to the fuel pump, it will lower the BP of gas. Of course, if it is indeed a non vented cap, after a while, the car will quit due to fuel starvation.

As Everett says, check the temp of the tank by the muffler.

alan

Yep, you can just use you hand for a guesstimate. When I had a cross flow, (two of them actually) I was worried about heat. But I don't remember boiling the fuel. If it seems too warm for your liking, loose the cross flow. It's your call.
Maybe something like this will pull your chain;
http://epitomesrebuild.com/images/242.JPG

Thanks for all the replies. I may loose the crossflow or try to insulate the tank a bit. I like the sound of the muffler and the extra ground clearance. I just don't think boiling the gas is a good thing. Not only will the fuel feeding the carb be hot but its scary boiling the gas. I know it probably isn't too dangerous and that a spark is required for combustion but I find myself opening the cap to relieve the pressure every time I've go for a drive.

:beers: