radiator holds almost a gallon, about half of the total. Might as well drain it all.

 

Is it necessary to drain the block?

Not necessary, however most people will tell you to try to drain as much as possible.

You will get 2/3 of the liquid out by only draining what’s in the radiator.

 

What is the coolant capacity?

This information can be found in your owner's manual...It's approx. 7.5 qt. for 4-cylinder and 9.5 qt for V6.

 

Why leave some old coolant in the engine when it's not that hard drain the block, especially the four cylinder engine. Go for it.