Hopefully someone here can shed some light on my odd XJ behavior. We were on a drive from St. Louis (about 600 ft above sea level) to Colorado, ending our trip on the far side of Monarch Pass. We were towing an enclosed 4x8 U-haul trailer with around 700 or less pounds of cargo in it. We kept the speed down, and the jeep didn't seem to mind the load. We filled up the gas in Colby, KS (about 3100 ft), drove to Limon, CO which is about 120 miles beyond Colby. We decided to top off there. When we cracked the gas cap, it was extremely rambunctious and spitty. Eased it open little by little, but it spewed violently and continued to hiss for a couple minutes. The gas was so agitated, that it took about 5 gallons before I could squeeze the gas handle without it clicking off. I was eventually able to lock the handle and let it fill up. We ran into extreme weather in Colorado Springs (about 5800ft) - hail, torrential downpours, etc. Everything seemed fine until we turned onto 285 at Buena Vista and started our climb toward Monarch (11, 312 ft.). The husband jumped on it a couple of times in order to maintain our forward/upward momentum, but for the most part, we just took it nice and easy (the whole drive was done in 3). Once on 285, I started smelling gas (but thought for quite a while that I was just smelling the husband after his run in with the turbulent gas tank). It got really bad as we neared the top of Monarch, which is about 6 miles of sustained steep grades (up to 7%). The temp gauge went a tad past middle, but nothing that really concerned us. Once we crested the summit, the check engine light came on, the gas smell went away, and the Jeep was happy again.

The oddest thing about this is that after all that turbulent gas and gas smell, we opened the jar of peanut butter we had in the cooler, and it was all frothy, too!!! Coincidence? Hmmm...

So, can anyone shed any light on our troubles? We have decided to take a different route home, as the Western side of Monarch is even steeper. Should we be concerned? Any ideas as to the origins of the gas smell? Any input would be highly appreciated.

 

First time at a high altitude, huh? The atmosphere has less pressure pushing on these items that were sealed at lower altitudes (14.7psi @ sea level), which are now pressurized. As for the peanut butter there must have been air pockets in it.

 

Not the first time at altitude for me or the jeep, but definitely the first time under a load. So, can you explain the pressure difference and its effect more fully?

 

Something that's sealed at a lower altitude has more air particles, packed tightly together. When you bring the item to a higher altitude, which is pushing on the item with less pressure now, the sealed particles want to be spaced apart like the surrounding air, so they're at a higher pressure.

 

Science!

 

I'm not really familiar with the evap system on the XJ, but is it possible the fuel tank was not being vented properly? I would think this would result in a CEL, though. Just thinking out loud...