Oil type viscosity / Regular or Synthetic ?

bigdog · 07-05-2021, 10:15 AM

I will be changing my oil & filter in my 2000 4.3L Mercuiser V6 this week.

I don't have an owner's manual, but what I have been able to research the manufacturer recommends 20Wx40 Synthetic oil.

I am the second owner, and the original owner always used conventional straight 10Wx40.

Questions:
1) Is there a major difference between 10W and 20W viscosity ?
2) Is there an advantage using 20W oil ?
3) Conventional oil vs Synthetic ? Is there a real advantage ? I know conventional oil contains carbon, which can leave deposits on valves and pistons, which can shorten life, but using in a boat where one only puts few hours use per year, would 'Syn' really make any difference ?
4) Thoughts regarding 'synthetic blend' oil ?

Feedback appreciated....

Thanks !

07-05-2021, 10:15 AM	#1
bigdog Senior Member Join Date: Apr 2006 Location: Central MA-Gilford Posts: 1,459 Thanks: 357 Thanked 126 Times in 100 Posts	Oil type viscosity / Regular or Synthetic ? I will be changing my oil & filter in my 2000 4.3L Mercuiser V6 this week. I don't have an owner's manual, but what I have been able to research the manufacturer recommends 20Wx40 Synthetic oil. I am the second owner, and the original owner always used conventional straight 10Wx40. Questions: 1) Is there a major difference between 10W and 20W viscosity ? 2) Is there an advantage using 20W oil ? 3) Conventional oil vs Synthetic ? Is there a real advantage ? I know conventional oil contains carbon, which can leave deposits on valves and pistons, which can shorten life, but using in a boat where one only puts few hours use per year, would 'Syn' really make any difference ? 4) Thoughts regarding 'synthetic blend' oil ? Feedback appreciated.... Thanks !