No, I didn't blow up.
Sorry about taking so long getting back on this.
It was a very disrupted holiday.
M'Lady broke her leg yesterday.

Ok I did go up the mountain Saturday and got some skiing in, somewhat.
I stopped at 7k', where I left the highway, and gave it a 10 min break.
The tank was not heating up, or pressurizing.
All was well.

Then, I turned onto the mountain access road, still paved but steeper and slower.
I stopped again at 9k' where the lower pavement ends.
The tank was heating up and beginning to pressurize.
The fumes I vented were warmer than they should have been.
But, it had not begun to vent on its own.
I vented the tank several times as it cooled down.
I continued upward on the dirt portion of the road to about 11k', stopping to vent the tank again.
It was still heating up and pressurizing.
Then, I stopped again at about 12k' where the upper road pavement began, vented the still warm tank and continued to the top.
Stopping to vent and allow the computer to reset several times helped a lot to keep it from over pressurizing.

When I went up the first time it had about 3/4 of a tank.
The last time it was a full tank.

If there is no fuel return line back to the tank, the fuel pump might be the source of the heat in the tank.
I had gone up there 2 or 3 times before a couple of years ago.
I never became aware of the fuel tank heating up and pressurizing.
But, I never checked it because it didn't over pressurize.

I find the idea of the fuel pump being inside the tank and causing the fuel to heat up like that disconcerting.
It's a 22gal tank.
It takes a lot of heat to raise its temp that much.

I'm thinking that driving slower on steeper road at altitude might be the source of the heating up.
This time I did the dirt portion in low gear with the engine revved up into its high torque range.
That may have helped to keep things cooler.

It's a '98 318 [5.2]

EDIT:
I found the part of the service manual that covers the EVAP system.
It was the last section in the book, right in front of the index.
I should'a known that's where it would be.
It describes the system, but doesn't seem to give much info for diagnosing it.

I assume that I need the '98 Powertrain Diagnostic Procedures Manual to dig into it and pinpoint the problems in the EVAP system.
I do have the '99 Powertrain Diagnostic Procedures Manual.
Is it too different from the '98 manual to use?

Its weird the tank gets warm...... That one is a real head scratcher. How warm is it getting? And does it only do it when you change altitude dramatically?

Hi HeyYou,
It really boggs my mind that it does this.
The vapors are quite warm, not hot.
It feels like a puff of warm wet air.
I can feel the gasoline condensing on my hand as it blows out. from under the cap.

I have never seen it do this before.
I have only noted it doing it after going above 7k' and no longer traveling at highway speeds, but down to speeds of 15 to 40 mph on both paved and dirt road.
The engine is working harder pulling a steeper grade.
If I do not stop to allow the computer to reset, there is a tremendous loss of power as the altitude increases ovet 10k'.
I will have the accelerator jammed to the floor and it will be all it can do to hold 15mph on the steeper pitches, yeah with the 318 and an empty box.

I've traveled over many long distance dirt and gravel roads in my travels around Alaska and Northern Canada.
Their conditions have ranged from almost highway-like to barely passable.
I have traveled over 10k'+ passes in the canyon lands of Utah, and Arizona, never seen this happen until here in Hawai'i.

I'm having a really hard time understanding what's going on.
I wonder if the ethanol gas has anything to do with it.

Yeah, I can understand the tank building pressure as you climb, that is perfectly reasonable. The gas getting warm though???? I can't think of any reason for that to happen. The fuel pump would have to be REALLY warm to heat up 20 gallons of gas....... to the point I would think your fuel tank would become a giant bomb.

I wonder if it has anything to do with the formulation for gas in hawaii?? Have you talked to other folks climbing the passes? Are they having any similar issues? Maybe have a chat with an off-road club in the area, see if they have any thoughts on this???

When I first became aware of this was a few days ago, the first attempt to go up to ski the mountain.
When I got to the 9k' elevation, the end of the lower pavement, they hadn't opened the road to the upper mountain yet.
I pulled into an area with cars parked all over the road and shoulders with people milling around.
As I stopped, I heard the fuel venting and saw the shadow on the ground of the fumes coming out of the filler tube.
I just about $h17.
I had visions of someone with a cigarette walking into that cloud of fumes.
It would probably ruin his day as well as mine.

It is possible that the grade would slope the tank so that the fuel pump might be out of the liquid fuel and cause the vapor above the liquid to heat up.
But, an almost full tank shouldn't do that.
Plus, if only the vapors were heating up, I wouldn't need to vent pressure over 1/4 to 1/2 hour to reduce the amount of fumes being generated.

I'm not a very social type.
I tend to be more of a hard core loner, very self sufficient.
It's not very likely that I'll go looking up an off roader group on this.
Not yet anyway, then I'd have to be sociable.

Supposedly, the gas here is the standard 10% ethanol mix.
I do wonder if it could figure into the problem, but assume it shouldn't if the powers that be have done their jobs.
And, they always do, right?

Almost all the other vehicles going up are newer than my old Dak.
They do not seem to have any problems.

Poking about the web a bit, most folks seem to be pointing at a fault in the vapor recovery system somewhere..... Either a clogged line, or malfunctioning valve. May not hurt to test the system, and ensure everything is working properly.

Been wrapped up in running M'Lady around from Dr. to Dr. getting her broken leg fixed up.
Plus, I'm now having to cater to her for the things she can't do herself right now, and having to do everything for myself she usually takes care of.
It'll be good to have her back on her feet and fully functional again.
I'm exhausted.

That was my thought also.
So, I'll re-ask my previous question:

Anyone know about this?

I've seen references to the diagnostic manuals, but, I have never actually SEEN the manual itself...... EBay seems to have some available..... for 01, etc. (I didn't look real hard...) but, there are like FIVE manuals from some years.....

i wouldn't think there would be too much difference from 98 to 99.