Rust scale in exhaust manifolds

It's normal and you don't need to worry about it.

I noticed that too when I drained mine. I could put my small finger up inside there and feel a bunch of rust flakes. I tried to drag out as many as I could. Thought about taking the water jacket off and cleaning it all out, but didnt have time.
Maybe I will use a magnet and pull out what I can before spring.

Not sure if CC ever had petcocks on their block drains, but one problem with rust in the engine is clogging up the petcocks. On any boat we have owned with petcocks, they were quickly replaced with NPT brass plugs (1/4" for the block). You can use a coathanger wire to poke around in the hole to be sure any chunks get pushed out with the draining water.

Justin,
Your manifolds are fine. What you are seeing with the flakes is from not draining and running the boat in hard water. It's called "plating" which is when mineral deposits form on a hot surface. It's very common in boilers and tube and shell heat exchangers if the water is not treated (softened). Drain and probe the holes on a regular basis. I suggest installing removable stem petcocks. I have them on all my boats. They are nice since the whole stem comes off so you can still probe the drain hole and they do not clog like the cheap radiator petcocks. McMaster has them up to 3/8" NPT so you will need to bush the exhaust manifolds. I suggest a 45 degree street el in the manifold, the bush and then the petcock. The large elbow will still give you plenty of room for probing.



Welcome to CCfan. How about some pictures and a diary entry?

Don't think I'd bother,they woun't be able to do much to the inside water jackets anyway. You could just pull them if you want and soak them in some muratic acid and give them a paint job. They are as efficient as you need. Save your money for some new ones in the future

Not only that but it may have been a long time since the plugs had been removed.

Having a garden hose handy is a good idea too (to quickly rinse off any spatter that gets on you). I try to stand upwind - you can see fumes when the bottle is opened!

I have a muriatic acid tank (55 gallon plastic barrell with a gal of acid in about 40 gal of water). I use it for steel, but dont like it for cast iron. I have only tried it a couple times with CI, but find it hard to get all the acid out of the metal's pores. I hear it can be neutralized with baking soda, but must be done multiple times? Also seams to rust very easily making painting it hard.. You guys have any tips I missed on it?



A friend suggested Evapo-rust. He swears by it. I am going to try it on a set of manifolds for my 73 this winter.


Has anyone ever tried electrolysis?

Before you go with the muriatic route, you may want to go with something safer. Lime-Away or there are products available from HVAC supplies. I have used them on tube and shell heat exchangers and they work great. The nice thing about them is they contain a corrosion inhibitor so when the solution gets to the metal, it doesn't start eating it up.

Electrolysis won't work on inside surfaces unless you can somehow get the get the anode inside the manifold and keep it from touching the metal manifold.