Whats the best way to flush / blowout the transmission cooler lines. Any should the check valve be removed?

 

You can buy cooler flush in an aerasol can at most parts stores. I never trust those check valves so I put in a new one with every transmission overhaul.

 

Use the arisol can and spray into the line that cool fluid comes out of (I don't know which one that is). Use about half a can and then let it soak momentarily. Gently blow air into the same line to remove your spray and any contaminants. That way, you back flush the lines instead of driving anything thru the coolers.

Repeat until the spray comes out clean.