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Coleman® Fuel Filler Cap Safety
You should always use a new replacement fuel filler cap on your lantern and stove whenever possible. The original cap looks nice for display, but it may not be the best choice for use.
Appliances prior to about 1963 have a 3-piece filler cap with a small hole in side that was designed to ventilate pressure while unscrewing the cap. This small hole has a 
tendency to spray a stream of fuel in whatever direction it happens to be pointing when depressurizing. THIS CAP CAN BE EXTREMELY DANGEROUS. If you don't believe me, read the snippet off to the left and click the link.
That cap was replaced in 1963, with a 3-piece design with "slots" on the inside intended to re-direct pressure down and away from danger. This cap was called the Plamann cap (see patent). In 1970 an even safer cap was introduced, a one-piece unit, and that is the cap being sold to this day.
* Special thanks to Alain C. of St. Hyacinthe, QC Canada to point out that Coleman Canada made 1-piece filler caps with a side pressure release hole in the early 1960s, and also used a Plamann-style 1-piece cap as early as 1965.
If your lantern or stove has an original one-piece cap that is no longer able to hold
pressure, simply replace the cap. If appearance matters, go to the hardware store and find a paint to match.
If you have a 3-piece cap and want to replace the gasket, make sure you have a new one first. You can't just go to the hardware store and buy it so you'll need to order one. Use caution: some on-line sellers (mainly on eBay®) use cheap materials, don't have a clue on sizing, and will sell you an O-Ring rather than a gasket.
An O-ring is round stock and is not intended to sit against the flat surfaces of the filler cap insert or fount. It can roll and/or flex during compression, causing an unwanted release of pressure and/or fuel. NEVER use an O-Ring in a filler cap.
I have also noticed some "Amish-made" fuel filler caps on eBay® that are an explosion waiting to happen. Not only are they lacking the slots of the Plamann cap to direct pressure downward, they don't even have the pressure relief hole.
"The cap, however, needs to have some type of ventilation capacity in order to equalize the interior pressure of the tank with that of the exterior atmosphere as the cap is removed. If the cap is without a ventilation feature, then removal of the cap will create a sudden pressure surge causing a discharge of fuel in a stream-like manner." -Volz vs Coleman Co., Supreme Court of Arizona Dec 17, 1987
Please take the fuel filler cap seriously. It is the only thing standing between you and disaster.
