How do you guys clean your upper plenums? Got mine clear of all parts from my '93 bonny, the outside is just dirty, but the inside is carboned-up.. Before I drop it in our parts washer at work, which is filled with Agitene, I thought I might ask.. I'm not sure what may or may not damage this plenum. Thoughts, please.. Mike

Send it to Will Wren. All the ones I got from him when I was sleeving them were spotless.

Seriously, I think he used Brakleen.

Castrol Super-Clean.

But in the long run, the grime on the inside won't really effect anything. And it'll just come back because of your EGR and PCV.

Keep in mind the upper intake is very likely Nylon. Make sure you don't use a solvent that will dissolve it or break it down chemically.

Thanks, I have already submerged in the agitene.. Agitene is safe for all metals and plastics, and the recommended brush material to be used in agitene is a nylon brush, when metal bristles are not prudent for the part being cleaned.
Yeah, I think you mentioned somewhere that the UIM is nylon.. Seems like a suitable plastic, the melting point of a 6.6 resin nylon is pretty high.. 6.6 nylon is used in household furnace applications, for the AC evaporator drip pan, which of course sits right above the heat exchanger. No rust issues like the old tin drip pans.

Mike