A couple more photos
You have a Century.
$5 is a hell of a deal. Just make sure to be gentle with the cap when you put it back on it should have a rubber seal under the cap to seal it shut so it wont leak. If the link doesnt work go to the lava library tab and down to the 1960s you should see Century listed.
Thanks for the help Cody. I actually was late to the estate auction and another couple bought a lot of lava lamps. One was one of those huge Chinese ones. This one was the only one that I felt looked older. I don't know how to date it but I would say 80s or earlier. Just my opinion. I put a bit of silicone grease on the threads to keep them from sticking and breaking. The glass tipped in the back of my car and lost about two ozs of liquid. Would it mess it up to add just water?
Some others here would be able to tell you more on the water part but I would not add any to it if it were me. Only way really to date one of those would be a sticker that would have been up under the cap and from you photos you already had the cap off which means that you did not see the sticker. They get loose over the years and if the cap had ever been removed prior the sticker was probably lost then. They are just a small disk sticker that had the model number and a date on them. You are probably right on the date for that lamp but that model and general style was made from the late 60s all the way through the 90s. The big Chinese lamps are neat but flow can be hit or miss so don't feel too bad as the lamp you have is a great lamp.
Also from you photos your lamp still has the heat reflector around the bulb...those are impossible to replace unless you luck into finding a base with one in it. When you take thr bulb out you will see what I mean. It is the metal ring/bowl that sits around the bulb.
Thanks for all the help. I thought I had missed it but the couple that bought the lamps sold it to me for 5 bucks. What a great surprise.
you could top it off but its a matter of choice
Just remember there needs to be room for expansion when hot
I'd leave it exactly as-is. It'sd not a rare lamp at all, but $5 is still a steal.
Nice score! A lot of us dream of such a great/cheap find!