What is the best way to clean a plastic inlet manifold? Is it safe to soak it with a mix of water and dishwasher overnight?
Edit: Is it safe to apply engine degreasers on a plastic inlet manifold?
Should not be an issue soaking it in water/dish soap (liquid - ie: Dawn). I don't think I'd run it through the dishwasher or use dishwasher soap. You could also use something like Simple Green. Engine degreaser like the "purple" stuff is just fine, but don't let anything soak in it. Use it, clean it, rinse it off. The purple stuff has a tendency to eat things ... I don't know about plastic, but it will eat aluminum. If there are any aluminum fittings in the intake, expect them to be damaged if you soak them.
Usually detergent or some have used brake cleaner ( but that was on manifolds with an egr connected) with usefull tools like scrapers, toothbrush etc and lots of elbow grease...