How much fluid in lower unit

[Steveo314]

I have a 1974 mercury 500 50 hp. And I'm changing
The impeller. Any hints. And how much fluid do I need

 

[racerone]

You do not have to change the oil to replace the impeller.---------If you do then one quart / liter is plenty to do it twice.

 

[Eric Hoare]

Just top it up until the oil flows out then replace the cap/ screw.