Or... A cautionary tale of non-AGM batteries.

I started smelling a slight fuel aroma while I was working under my Cayman. I pulled the belly pans and started poking around. I could see what looked like some splashes of fluid above the rear of the fuel tank.



So, I started digging in to the topside. Removed the battery and there was a ton of corrosion on the tray. The battery is a non-AGM aftermarket model. The car is heavily track-prepped. I assume the PO went with the non-AGM to save a few pounds up high. Under the battery tray, I can see the source of my problem. In this picture, you can see further corrosion on the fuel level sender connection and the cracked white plastic flange. My operating theory is that the battery leaked on the plastic tank flange, eventually causing it to crack. New flange and gasket on order. The car has been subject to a couple of good impacts, so that couldn't have helped matters. Has anyone done any fuel tank work? Anything else I should be wary of?

 

AGM battery, I think.

The 987 has a clear plastic vent hose going from the top of the battery to the outside of the car. If that's not there any acid leakage will run down the side of the battery. Even the AGM batteries have a connection point for this, though theoretically those should never leak liquid.

From what I'm reading the 981 cars don't have a vent line, so I guess if you install a standard battery and it leaks it'll run down the side.

 

AGM, right. No vent hose on my 981. I'm just going to replace it with an AGM. I'm too cheap to step up to a li-ion :-).

 

For future reference, this tool is a perfect fit for the fuel tank locking ring: https://smile.amazon.com/gp/product/B07G8YJXGL