Propane

From VanagonWiki

Propane Level Gauge?

• Unfortunately, there is no "Level" gauge for these tanks. A "Pressure" gauge would continue to show pressure until you ran out of propane. In other words, the gauge wouldn't drop with usage, only when the tank goes empty. The tanks are too thick and our propane usage is too slow for using those glue on strips that show a difference in temperature (Mike Collum).

• Small tanks like a BBQ tank have three options. One is the magnetic strip that sticks to the side, and basically registers changes in temperature. The changes in temperature are quite small, but enough that the thermosensitive ink or marker is able to give a general idea of what is left. A pressure gauge does exist for BBQ tanks and for RVs, however as a couple astute members pointed out, and as even pointed out by the website of the company that makes it, the gauge really only gives you an emergency warning when the gas is almost completely gone. According to the web site, you only have about 10-15 minutes of gas left once the tank gets into the red zone.
  Granted, there is a yellow area on the gauge that is supposed to tell you when you are having the "warning signs" of running out of gas, but it is pretty small, and my guess is you would go from yellow to red to out in about 20 minutes. There is also a scale based gauge - weigh the tank, and when it gets below this weight, you need gas. For very large tanks like the one I have sitting out back of my house, apparently they use a float on the gauge of some sort, almost like a gasoline tank would. I did not find out a whole lot about this, but that would explain why the gauges on all the propane tanks I have seen only go down to about 10% - that is about 50 gallons in a 500 gallon tank, and I would guess the float is simply not accurate much past that point.
  So, where does that leave us? There is no room in a little Westy-sized tank for a float system, or at least not that I have found. Perhaps a very small float could be devised, but I doubt the market is that great for it. The stick on systems won't work because A) our tank is not vertical, so the temperature change would be hard to track and B) one of the list members mentioned our tank walls are a lot thicker than a BBQ tank. Can't verify that, but might be true. And of course, a weight based system doesn't work on a permanently mounted tank. While it is quite easy and relatively cheap to put on a pressure based gauge, I really think the true effectiveness of such a system is pretty minimal. The last thing anyone wants to do is find out after getting set up camping that, "oops, only got 15 minutes of cook time left." But if anyone wants to read more about that system, it is at www.flameking.com.
  So, while the short answer to the question was - "You can't put a gauge on that tank," the longer answer is that the above are the reasons why (David Johnson).