crazing of rear window

Today I discovered overnight crazing of the rear window, immediately adjacent to the fuel filler, in a area just larger than a spread-out hand. The tank had been filled yesterday. The temperature rose more than 20 degrees F in under 24 hours, and fuel tank venting occurred. To worsen matters, The soft flannel sheet I use to cover the entire canopy & rear window in the hangar also draped over the fuel cap, became fuel-soaked in this event, possibly adhering to the lexan & painted aluminum and causing the immediate area to be fuel-soaked, also possibly impeding the vent in the fuel cap.

The crazing consists of dozens of very small parallel cracks, traveling longitudinally, not associated with any screw holes. Some of them begin at the aft edge of the lexan, others begin & end in the open. At first I suspected mechanical stress; now I'm leaning more toward a chemical reaction.

I have ordered a new rear window and decals for the fuel cap and canopy latch. However, since the damage appears to be cosmetic, I have no intention of actually replacing the rear window 'til I'm sure what caused the damage.

The fuel in this case was ethynol-free high test auto fuel. There is no way of knowing for sure what's in the gas we buy. I've "heard" that it may contain stabilizer, freshener, and/or injector cleaner. I've also "heard" that it really does contain ethynol, but also an agent to neutralize the water gathering properties of the ethynol.

So, guys...what happened to my window, and how can I be sure it doesn't re-occur?

Thanks,

Jim

Search in the RV12 forum for "crazing" and read the threads. LOTS of good information, particularly in thread #89721.
How full was your tank before the temperature rise? Do you have the Moller gauge? At about 15 gallons my Dynon indication pegs, and you can fill with the Moller a little past F before it starts coming up the neck. The Moller pegs when the top of the float hits the tank top, the tank is not yet full at that point.

Was your rear window sealed when it was installed? Your crazing is most likely caused by fuel reaching the unprotected edges of your window, either along the edge or around a drilled hole. The surface of the window has a protective coating but the cut edges/holes are unprotected. That's why I am curious whether your window was sealed to the rear baggage skin or not.

Randy,

No my window was not sealed. So I think you're right. Also the tank was clearly too full, so the drastic temperature rise did me in with a substantial purge of fuel. Plus my flannel sheet probably tended to hold the petroleum in place.

lesson learned. The replacement window will be sealed in that area. The tank will be left with expansion room, and the vent will be unobstructed.

Thanks.

Jim