Recently I put a 3" lift on my 2001 Sequoia and outfitted it with Skid plates and BFG KM2's. As a previous CJ7 owner, I know some really tough trails, that are wide enough to slide the "Griswold Family Truckster" through. Yesterday I gassed up and hit my favorite trail. In 8 miles, we gain 3500 feet, and it is very rough, very steep the whole way, rock crawling, bouncing etc. When we got to the top, I could hear what sounded like "boiling water" in the gas tank. I pulled the battery cable, thinking all the bouncing had caused the fuel pump to stick on. The boiling sound continued. I unscrewed the gas cap, and about a gallon of gas shot out, that gas was hot. I put the cap back on, and the sound continued. I did this cap on/cap off exercise about 10 times thinking the pressure would normalize and stop. It did not. I finally put the cap back on, and walked away, wondering if I had some kind of fire inside the tank or pump, that was going to blow up. About two hours later I went to check, and it had finally normalized. Drove out the next morning without incident, and it seems ok today. Can anyone explain this? Is this a stuck valve in the EVAP system or Charcoal Canister? The Purge line being flooded since we were at a steep uphill angle for so long with a full tank? I was scared ****less, I really thought we had a fire brewing. Any ideas?

 

After some research, I'll post my findings here for others. There are many different gasoline formulas - including summer and winter. Summer gas is supposed to boil at approximately 124 degrees. Winter gas boils at approximately 90 degrees. As elevation is gained, atmospheric pressure lowers, which lowers the boiling point of gasoline. Gas comes out of an underground tank at approximately 55 degrees. So, a full tank of cold gas, which may have very likely been an early fall/winter blend, or leftover winter blend from a small town gas pump, immediately subjected to a 3500 foot elevation gain, at 96 degree outside temperature, and surely higher temps under a slow moving 4x4 results in a tank full of boiling gas. Several things to take into consideration here - not filling the tank completely, perhaps stopping for lunch to let the tank warm and expand before heading up the trail, perhaps stopping for a break every hour or so to let things cool. Hope this helps someone else. I've seen this problem posted in a few forums, but no good explanation could I find.