If you have a large enough surface area maybe but on a thin section for crack repair it just doesn't hold well. Not that I've looked into every option because once I got a plastic welding kit I didn't see the point. It's basically just a soldering iron with a wide tip and some stainless mesh but it does a much better job if you're not concerned about appearance.
That said for timing belt or spark plug covers I'd probably just cruise the classifieds for replacements.
