Full tank

[Dood]

Finally, I know who is siphoning my gas!

I drive my swepty to a bus park and ride to get to work everyday. The thing has terrible gas mileage which I've been tracking and trying to remedy. I've noticed that some days when I park it with a full tank that it would only have three quarters of a tank left when I got back in it at the end of the day. At first I thought the sender or gauge was goofy so I checked it w/ a DVM. Then I started to get paranoid that someone was siphoning the gas.

Well, anyway, the parking garage is an adjacent parking ramp style where the parking aisles are the ramps which means that for most parking spots your vehicle is on an angle relative to its front to back centerline. So today I park the truck with a spanking new full tank on the ramp with the driver's facing downhill. For once, I went home early and it was still light out so I could see in the garage and there was a huge puddle of something running downhill from my swepty! When I got close enough to open door I smelled gas. There was fuel all down the side of the truck. Then, like a dumbass, I opened the gas cap to 'check things out' and was greeted with about a half gallon of gas on my 'work' clothes.

Long story short: when I park my truck on a side to side incline, gas leaks out the filler neck at the cap (I think).

Should I get a new neck from Steele? or a new cap? or just not fill it past 3/4? Anyone else have this problem?

[surfnuke9]

The only other place for a leak to occur from the filler neck (than the cap) is the grommet type seal where it enters the tank.

If it was leaking there you would have known by now since you would be having gas inside the cab.

Sounds like you need a new cap. Make sure you get the right (vented/non-vented) cap for your truck. Some tanks have vents and others do not.

either way, the tank needs to be vented or it will develop a leak.

[Dood]

Thanks for the tip! I'm not totally sure where the leak is. The cab frequently smells of fuel. How do I know if it is a vented vs non-vented tank?

I found tastypinecone's build thread where he had a similar problem:

...every time I take a right turn above five miles per hour gas would leak out of the cap and into the cab past the body/filler neck gasket.

I'll try to grab a picture of inside the cab and the cap. As an aside, I had a scary experience a month back when I tried to fill the tank by using the gas stations nozzle's auto-shutoff: before the shutoff flipped and stopped the flow, the tank built enough pressure to blow the nozzle free from the filler neck. I had my head under the hood and was checking the oil when this happened.

Edit: found more posts on this,

• gas tank where mbalbritton described a series of leaks and venting
• As if my gas mileage wasn't going to be bad enough... another mbalbritton fuel leak

[wally426ci]

I have the same problem, need to find a good cap myself.

[mnwebb]

Is there any harm in having a vented gas cap and vented tank? My 66'D200 always smells like gas and it appears that someone added a vent in the tank (behind drivers seat) with a rubber tube that goes down thru the floor. Photo below. Would people recommend capping that tank vent and just going with a vented cap?

Also any recommendations for filler neck seals, both the one under the cap and the filler neck to tank? My filler neck has no overflow tube, guessing that was normal in 66?

Thanks!

[1970D300]

Fuel is stored in underground tanks where it stays cool.

Fuel expands with any rise in temperature.

So..... Do not fill a tank all the way if it is going to sit right after in a warmer environment.

[martincom]

Is there any harm in having a vented gas cap and vented tank? My 66'D200 always smells like gas and it appears that someone added a vent in the tank (behind drivers seat) with a rubber tube that goes down thru the floor. Photo below. Would people recommend capping that tank vent and just going with a vented cap?

Also any recommendations for filler neck seals, both the one under the cap and the filler neck to tank? My filler neck has no overflow tube, guessing that was normal in 66?

Thanks!

Here is a link for a replacement filler neck/tank grommet:

https://www.amazon.com/gp/product/B07VJ ... UTF8&psc=1

The fuel caps are available at the parts stores. I purchased one from Rock Auto last year.

What is the capped off port on your tank for? The filler neck vent???

Typically, non-vented caps are utilized on tanks that have some other venting arrangement. For example, my '71 was a CA truck. So it's vent is ultimately plumbed back to the crankcase breather, on the valve cover.

[mnwebb]

The small cap in the photo was temporary as I replaced the line that goes from that down thru the floor.