Fuel tank swelling

[Roamad]

My C-Dory has a 12-gallon red plastic fuel tank. On very hot days it puffs up like a balloon, I assume because the fuel/gasses inside expand from the heat. If I crack open the fill cap the gasses escape and the tank shrinks back to normal size. Should I be concerned about this damaging the tank? What should I do about it? It’s a new tank and I’d prefer not to replace it for a long time.

[Tom Hruby]

I would suggest you avoid placing your plastic gas tank in the sun, or provide some kind of shade for it. Google AI has a fairly decent discussion of how the heat affect the plastic (see below). The other warning is that you should never try to release the pressure in the tank by opening the top when hot. Hot gasoline is very volatile and can cause an explosion if there is any source of a flame or static electricity near by. The flash point of gasoline is -45 degrees F, so any source nearby will cause an explosion.

From Google":
How heat and swelling degrade plastic fuel tanks
Accelerated oxidation and cross-linking: Heat and exposure to oxygen, or thermal oxidation, is a primary cause of polyethylene degradation. The molecular chains of the plastic are broken down, which makes the material more brittle over time.
Chemical-induced stress cracking: Hydrocarbons in fuel, especially with ethanol blends, can cause chemical stress that exacerbates heat-related degradation. The combination of heat and chemical exposure can soften the tank walls and lead to stress cracks, which weaken the tank.
Mechanical fatigue: The repeated swelling and contracting of the tank due to temperature fluctuations creates mechanical stress on the plastic. This fatigue can cause invisible micro-cracks that grow larger over time, potentially leading to vapor leaks or a rupture.
Increased permeability: Higher temperatures increase the rate at which fuel vapors permeate through the tank walls. This not only contributes to the swelling but also causes fuel loss and increased emissions.
Structural weakening: Temperatures exceeding 120°F (49°C) can cause polyethylene tank walls to soften. While the material may return to its original shape when it cools, this softening can permanently deform the plastic and weaken its integrity over time.

[ssobol]

[Roamad]

Thx for the replies. I will try to shade the tank somehow. I keep the boat in an uncovered slip, so I’ll have to get creative.

[thataway]

If you use a canvas shade, then be sure there is adequate air flow under it. I tend to let my tanks like this vent to the athmosphere....better than a burst tank.

[Roamad]

Not gonna pay attention to any info coming from AI. It’s a long way from being trustworthy. But I will find a way to shade the tank, because that sounds like good ol’ common sense.