My Imron is going on 8 years without a problem. If it's not prepped correctly it will just peel off in sheets.

I've used imron for years on my intake manifolds, exhaust manifolds and even aluminum valve covers etc with no problems at all. Its just under water applications it doesnt hold up on. I left the boat in the water for one season after having it rack stored for the first couple years...and the paint start peeling off the drives after that season in the water. It was fine for the 2 years I had kept it on the rack. I asked the paint shop about it and they said that imron is not rated for constant under water applications for that exact reason.