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Question
I have twin 1996 mercruiser 7.4 MPI's w/ vdrives- 709 hours located on Chesapeake Bay. Closed cooled block/raw water cooled manifolds & risers(replaced by me in 2006). New raw water pumps in 2009. I am a stickler for maintenance. The closed cooling systems were drained and filled @661 hrs/18 months ago. Ph test strips OK & freeze level hydrometer to -15 degrees. Service manual says to replace coolant every two seasons. Should I drain and refill now? Also, fresh water coolant hoses are soft and pliable but never replaced to my knowledge since 1996. Should they be replaced now?(I have one spare set onboard for emergencies).
Submitted: 18 days and 17 hours ago.
Category: Boat
Value: $15
Status: CLOSED
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Optional Information
Make (of engine): mercruiser
Model (of engine): 7.4 mpi
Year: 1996
Horsepower: 310
Accepted Answer
Hello. If your antifreeze tests OK and is clean, I would not necessarily replace it. However, I think I would want my antifreeze to test to less than -15; as I recall, a normal 50/50 antifreeze mix tests to -37, so yours may be a bit diluted. Minus 15 is probably fine for your area, but... It certainly can't hurt to drain and change, or you can just add some straight antifreeze to bring the protection level up some. But, I would be concerned about those hoses and I WOULD replace those - you don't want to have to do that in the middle of rough water (been there, done that!).
Expert:
Captain Dave
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Answered:
11/4/2009
Marine Mechanic
USCG Licensed Captain, 20+ Years Boating, Fishing, Maintenance and Repair Experience
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