fuel tank pressurizes on 68d100

[dodge_68d100]

I have a 68d100 utiline pickup which recently started having gas seep out from under the gas cap when parked after running and run down the cab. My tank is behind the seat. I replaced the gas cap with a new one from NAPA. It seems to be better now but I can hear the cap whistle a little after I stop driving indicating it's venting/building up pressure in the tank. When I unscrew the cap there is a lot of pressure behind it after driving. I can also smell the gas in the cab because of this buildup. Is this normal to have this type of build up? If so what causes it? The truck only has 28K original miles with the original fuel pump. No other problems with the truck.

Thanks Greg

[wideblock]

the only time i have had any of mine do this is on a really hot day. not sure what would cause that much pressure from running. are you sure its pressure and not vaccume on the tank??

[Jeffc]

A 68 should have a vented cap, do you have one?
or is it the later non vented cap?
If you do have vented cap, does this happen when the
tank is almost full, like over 3/4 of a tank or more?
or all the time?
Vented cap will have a hole in the center with a
piece that will close it if fuel reaches it, cap will
rattel a little if shaken.
If for some fluke that you have a later tank installed
with a vent line (2nd line off the fuel sending unit)
you need to make sure this is doing its job and the vent line exits the cab.
Agree with what Trey said here, if it is building pressure on the inside it is because of having the sun on the back of the cab or making a lot of heat from windows.

[dodge_68d100]

Yes, it's a vented cap with only one line out of the top of the gas tank. The NAPA replacement looks exactly like the original gas cap & it does rattle when shaken. It does seem to happen when the temperature is hot outside & when the tank is 3/4 to full. Since I don't have a working fuel gauge and my gas tank sender unit also doesn't work I keep the tank very full. I'm in the northeast so the temperature just started getting warm about 60-70 outside. Yesterday I went for a ride w/ 3/4 tank full and parked. I then opened the gas cap slowly and could hear pressure release or vacuum being pulled into the tank - not sure which. About an hour later with the truck in the sun about 75 degrees before starting it up I opened the gas cap slowly and again could hear pressure release or vacuum being pulled into the tank?

Today with the truck sitting in the sun about 75 degrees I could smell fumes from the vented cap as I sat in the truck about 3/4 full tank with the engine cold. This seems to indicate that the tank is building up with pressure/vapors and releasing it thru the vented cap? Is this normal action on a hot day

Thanks for reading,

Greg

[wideblock]

sounds like your cap is doing its job of venting. what condition is the rubber between the cab and filler neck? i used to get a lot of smells from gas in the cab before i replaced mine, now i dont. also, on a hot day with a full tank, dont park at any angle where the gas cap is on the low side, i did this once and came out to a puddle. pressure built up in the heat, but the liquid was over the vent hole, when pressure got high enough, it pushed gas out till the air could get to the hole to be released.

[dodge_68d100]

The hose in the cab appears fine and there is no smell in the cab with the windows rolled up. I hear you on parking level. I too made that mistake last year with a full tank of gas. Came out to a big puddle on the pavement, again it was a hot day.

It's just hard to imagine it's building up that much pressure in the tank even with my windows down. Outside temperature is only about 70 so far and it's going to get much hotter soon.

Later
Greg

[wideblock]

it seems to not be the temp that gets you, but the direct sun on the back of the cab, or coming thru the wind shield. it may be 70 outside, but in the sun that cabs 100 inside

[Jeffc]

You may want to get some padding with the foil backing
and rapp your tank in it, they sell this for floor boards, helps keeps heat of the exhaust and engine from coming though the floor of car/truck.
You can use contact cemment to hold it to the tank,
but to get it on the back side you will need to pull the
tank, will help to keep fuel temp in the tank more in control and building pressure, just a thought.......
May not stop it all but will slow it down a lot
as bear metal will transmit heat fast.

[dodge_68d100]

Thanks for the info guys. Insulating the tank sounds like a good idea, can't hurt.

Trey,
I sent you an email last week from a different email address on the possibility of a working fuel gauge and working sending unit for my truck. Any luck? I have tried 4 different gas gauges so far but they have all been junk. Once I had a working fuel gauge I was going to move on into finding a working sender unit assuming once I pulled my out I couldn't fix it.

Thanks
Greg

[farmhand66css]

Greg, where in the north east are you? I think I have a good gauge from a 68. I am in Rhode Island.

Parked my truck on an incline came back to a puddle on the groung and wrinkles in my new paint job

Matt

[dodge_68d100]

I'm right next to you in Bellingham, Ma..

Very interested in a working gauge.

Thanks
Greg

[farmhand66css]

Greg,

I have a working gauge and sending unit. The sending unit is rough. send me a note if you are interested mskdesigns@att.net. I will send you my address and phone#

Matt