anyone use THERMOCURE?

While draining the coolant I noticed it was more rust than anti-freeze. My guess is with the mostly short trips, I get air bubbles in the system and causing rust or I never cleaned the block properly when I got the car (it sat for 10 years).

Anyway I need to cure this problem. Block is out of the car, I don't want to tear it down to get it hot-tanked either :/

Any advice to clean out the rust is appreciated.

If possible, pull both block plugs so you can fully drain.

I usually just flip it over lol

I wonder if I just fill the block with vinegar and rinse it out a few times to clear the coolant passages while it's on the stand?