took a set of heads in to get hot tanked, they were not very greasy just wanted the old paint off and carbon out of the bowls and heat crossover. well picked them up and looks like it removed the paint but didn't touch much of the carbon or light flash rust, in fact they look more rusted than before. what gives? last few times i had heads cleaned they came out like new.

Likely in the past the machine shop used a hot tank filled with a caustic solution but now in the interest of being a "green" world the EPA has made that equipment illegal so instead your heads were put into an industrial dish washer... If you pay for the next step some form of shot blasting they would be free of rust and carbon deposits...

shot abraded this block and came out great. A tip is to thoroughly soak your parts with WD40 and cover them with trash bags after and they will be amazingly clean indefinitely

I have them airless-shot blasted. Most cleaners now-a-days are not really strong anymore due to EPA mandates and DEP fines. I watched a program once on a southern CA shop building an engine for Boyd Coddington and they used a pressure washer to clean the block. That would be a huge fine if anyone saw you doing that as a business in CT unless you were reclaiming all the residue.

my machine shop bakes it in and oven,then rinses the block and air dries it.

the carbon turns to powder and cleans right out,then they wash it down with purple cleaner and rinse

Thanks, thats what i figured, so its just a waist of $$ to just ask for a hot tank. other than if you want old paint removed. It did remove the paint .

How do they protect the machined surfaces when shot blasting?

I'm having one cleaned and pressure tested now, they bake them and then tank them at this shop.

When I've done them at home I have just soaked them with Gunk and then used my pressure washer hooked up to hot water, turns out amazingly clean.

I used large diameter rubber hose in the main bores with the caps torqued in place and slit pcs of heater hose in the lifter bores. With those in place there was no damage.