Fuel Tank pressurized when off

[Roger_850T]

Hi Everyone,

Here's a new problem for me, didn't find it in a search of the forums, so I thought I'd ask.

'95 850T, 328k miles. It's been off the road for 3 months while I did some work, (replace turbo, engine mounts), first drive out today.

When I get home and park in the garage, and shut the car off, I hear a "whoosh" noise continuously from underneath, in the vicinity of the fuel filter. Maybe more like Shhhhhhhhhhhhhh…. It's pretty continuous. I opened the fuel filler cap, and a lot of pressure vented from the fuel tank. I then hear a gurgling, like something is boiling somewhere. If I replace the cap, the whoosh comes back. Repeated 2 or 3 times, same behavior. It sounds like something is boiling the fuel, causing the system to overall pressurize, and there is a pressure blowoff valve somewhere that is venting to protect the fuel system.

Thoughts:
- I had the turbo off, did I put something back wrong? Maybe missed a heat shield? (No extra parts that I'm aware of...)

- Car was last filled up in March, it has winter gas (higher volatility for better cold starting), and today was well over 90F. Car's thermometer was reporting 108 when standing still. Is there enough difference between winter and summer gas to make a difference here? Tank is 3/4 full.

- Could something have become plugged?

- Fuel cap is demonstrably sealing properly.

- No check engine light or codes.

- Listened carefully in engine bay - boiling noises seem to be coming from farther back. Inspected fuel lines down the back of the engine, nothing unusual noted.

Any thoughts on what might be going on? TIA for any input!

Roger

[abscate]

Run the tank down to 1/4 and see it gets better. They are sealed up and a 108F day puts a big vapor pressure load on the evap system

Reid vapor pressure of a winter blend could be 12 psi which is getting pretty close to boil off.

Road trip!