Coolent Replacement

Question
My 350 Marine Power FW cooled gas engine has a 50/50 mixture with about 300 hours. I am having a slow over heating problem. Does this anti-freeze mixture lose it's heat transfer capabilities with age? Thank You.  

Answer
NO. YOU SHOULD LOOK AT THE RAW WATER IMPELLER FIRST. COOLANT LEVEL SHOULD BE FULL. THE IMPELLER NEEDS TO BE CHANGED EVERY YEAR. YOU DIDN'T SAY HOW MANY HOURS OR THE YEAR OF YOUR ENGINE. THE ELBOWS ARE GENERALLY GOOD FOR 5 YEARS, BUT YOU MIGHT CHECK THEM FOR BLOCKAGE FROM CORROSION.

HOPE THIS HELPS  BRUCE