question on gas caps (FJ40)

[w2hx]

Hi all,

The gas cap that came on my 78 FJ40 has a lock on it. Not only does the cap have a lock, but so does the little door to access to gas cap. Both keys are different. Seems like an awful lot of protection for some gas. So I wanted to get a simpler gas cap. It is a toyota part and seems to fit fine. But I wonder about something. The cap that came with the truck is much deeper. The replacement is very shallow. Here are some pictures (original on the right, new on the left).

http://www.w2hx.com/x/FJ40/IMG00048.jpg

http://www.w2hx.com/x/FJ40/IMG00049.jpg

Can anyone think of a reason I should be using such a deep cap? Anything to do with evaporation or fumes or anything?

One other piece to the puzzle. Whenever I open the DOOR to the cap (not the cap itself) just the door. It seems some pressure is relieved within the tank. It must be that the door is helping to keep the cap pressed tight against the filler neck. Is this normal? Or should the cap keep the pressure and not rely on the door?

I have not tried the new cap to see how it behaves, BUT (question #2).

I have seen pictures of other 40's that have NO door at all covering the gas cap. I LIKE that look! I suspect it might be earlier cruisers?

I am considering taking off the door and the little catch on the top of the doorway. And using this new gas cap. I am not too concerned about people steeling gas from me.

Door
http://www.w2hx.com/x/FJ40/IMG00050.jpg

So:
a) any reason I can't use this shallower gas cap?
b) Is the door supposed to be part of keeping pressure in the tank?

thanks
(sorry in advance for the huge pictures. I have to figure out how to reduce them)
(LEFT CAP = NEW) (RIGHT CAP=ORIGINAL)

 

[dgangle]

you can tell by the marks in the paint on the inside of the door that longer, locking cap is hitting. Throw it in the trash and use the standard non-locking cap. As long as it fits properly I wouldn't worry about it really. Problem with 2 diff key solved.

Plus it will look retarded with no door

those dinky locks are not going to stop a determined thief, not even ever a stupid one

 

[KillerPea]

I'm pretty sure the larger cap has some sort of vent built into it. I switched to the shorter gas cap last week on my 78. When I got home from work today (it was relatively hot and I had a full tank) there was a huge puddle of gas under my truck and my tank was fully pressurized when I pulled the new cap off.

 

[w2hx]

dgangle: Thanks for your input. Just so I am clear on your opinion here. You think it would be a-ok to remove the door and catch, but silly to then have a locking cap there? I think I would agree with you!

Killerpea: Obviously I am interested in your experience here. Is your larger cap the same or similar to mine? Is tomorrow's weather in Dallas going to be close to todays? Could you do the same experiment with both?

 

[Doug_S]

I'm pretty sure the larger cap has some sort of vent built into it. I switched to the shorter gas cap last week on my 78. When I got home from work today (it was relatively hot and I had a full tank) there was a huge puddle of gas under my truck and my tank was fully pressurized when I pulled the new cap off.

Mine does exactly the same thing except I haven't had the puddle of gas under the truck. I've had three different non-oem caps on it and all have allowed the tank to pressurize. Any ideas? I've been told that there is a pressure vent on it that, when it gets to a certain pressure, vents. Is this true? I'm tempted to drill a small hole in the cap to vent all the time.

 

[w2hx]

Is pressurizing such a bad thing? Maybe its supposed to do that? My moder toyota has a note that says the tank may be pressurized to remove the cap carefully. Maybe the pressure helps the fuel pump? Maybe its supposed to develop pressure?

 

[Doug_S]

I don't know either. The truck's tank was so pressurized once that I was worried that it'd blow off a fuel line. I think I'm going to go OEM and see if that solves the problem. OEM is always better anyway.

 

[PabloCruise]

Your gas tank came from the factory with a evaporative control system to deal with pressure that builds up in a tank from gasoline changing temperature.

These systems actually work and do not need to be removed. They will keep puddles from forming (and burning down your garage) as well as keeping harmful vapors from building inside your rig.

Do a search...

 

[Doug_S]

Unfortunately, like many others, the PO removed all of the evaporative control equipment from the truck. It looks like I'll have to drill a small (#50) hole in the cap for it to vent correctly.

 

[Trollhole]

you can tell by the marks in the paint on the inside of the door that longer, locking cap is hitting. Throw it in the trash and use the standard non-locking cap. As long as it fits properly I wouldn't worry about it really. Problem with 2 diff key solved.

Plus it will look retarded with no door

those dinky locks are not going to stop a determined thief, not even ever a stupid one

X2. Small cap.

 

[Shawn Russell]

Dont drill a hole in the cap. As you go around corners with a full tank, you will leak gas and it will run down the side of your cruiser. Just go get a VENTED cap from the local parts store.

Shawn

 

[edwjmcgrath]

Ditto. Why would you even think about messing around with gas leaks?
If you don't have evaporative control then you need to vent the tank at the cap.
For $5 you can get a non locking, vented cap.

 

[Doug_S]

Yeah, that's what I thought that I was getting when I went to CarQuest Auto Parts. The guy assured me that the cap was set to vent when it reached a certain pressure which is too high in my estimation.

 

[ducktapeguy]

I picked up a keyed gas caps just like that one from O-reillys when I lost mine on the road somewhere. It didn't fit, the door wouldn't close properly with it. It looks like you have the same problem.

If you don't like the door, you could always retrofit a jeep fuel filler into your cruiser, but personally I think it would look pretty bad. An easier way would be just to remove the lock tab and stick a magnet on the back to hold it closed. But if you do decide to remove it, let me know, I need a spare fuel filler and door.

On a related note, are gas caps standard throughout all the years? My original one (1975) looked like this

Amazon.com: FRAM PRG-806 Fuel Cap: Automotive

I thought it was OEM, but after looking through some parts site I can't seem to find the same type, so I'm not sure anymore. And the fram one has the tabs oriented 90 degrees off so it hits the fuel door when closed. Is there an OEM style that looks like that?

 

[Shawn Russell]

No, they are not all the same. There are different widths (some were regular gas, some were unleaded gas).

The locking one is longer in order to hold the "locking" parts.

 

[PabloCruise]

I would urge you to consider putting the evap/vapor system back on.

 

[Trollhole]

Can you see it? Sitting about 9:30. Follow that line both ways and let us know what it's attached to. That is your vent.

 

[numby]

The factory style '78 era gas caps are vented... to let air IN as fuel is used up or during contraction/cooling of the vapor in the tank itself. The charcoal canister input marked "TO TANK" is the pressure relief valve. Make certain it's not clogged by blowing into it. Air should flow out all the other vents. If that is functional but you're still getting excessive pressure build up in the tank check to see if you have one of the white check valves installed between the vapor separator (behind the passenger seat) and the canister. If it's clogged you can remove it temporarily to see if your condition changes or even temporarily disconnect the charcoal canister itself to see if the vent line is functional at all. Do not plug the vent line back to the tank. You'll smell fuel in the engine compartment but at least you'll find out if your lines are plugged.

KillerPea: In addition to the above, you've probably got a hole or loose clamp in your fuel lines or maybe the vent line to the canister. Your pressure build-up is not being vented correctly by the canister and has found another way out!

 

[bsevans]

The factory style '78 era gas caps are vented... to let air IN as fuel is used up or during contraction/cooling of the vapor in the tank itself. The charcoal canister input marked "TO TANK" is the pressure relief valve. Make certain it's not clogged by blowing into it. Air should flow out all the other vents. If that is functional but you're still getting excessive pressure build up in the tank check to see if you have one of the white check valves installed between the vapor separator (behind the passenger seat) and the canister. If it's clogged you can remove it temporarily to see if your condition changes or even temporarily disconnect the charcoal canister itself to see if the vent line is functional at all. Do not plug the vent line back to the tank. You'll smell fuel in the engine compartment but at least you'll find out if your lines are plugged.

KillerPea: In addition to the above, you've probably got a hole or loose clamp in your fuel lines or maybe the vent line to the canister. Your pressure build-up is not being vented correctly by the canister and has found another way out!

The factory 78 cap is not vented. Everytime I go through emmisions they check both of my gas caps and confirm that they do not vent.

 

[numby]

The factory 78 cap is not vented. Everytime I go through emmisions they check both of my gas caps and confirm that they do not vent.

The caps do not vent outward to atmosphere but, instead, vent inward to allow for the contraction of tank volume. They ONLY let air in.

If you wrap your hairy man-mouth around the center portion of the cap and try blowing you won't be able to. But if you suck you'll feel that the one way check valve will allow air to flow... along with the delicate taste of unleaded... right into yer pie hole. Enjoy!