Can you use car oil in a Mercruiser 3.0 engine

[1985 Century Mustang]

I was going to use 10-40 regular car oil in my 1985 Mercruiser 3.0, is this a no no, or a yes yes.

 

[Bt Doctur]

25w-40, 20w-50 straight 30 but not 10-40

 

[Fun Times]

 

[Scott Danforth]

make sure the oil for your flat tappet motor has zinc in it

 

[1985 Century Mustang]

make sure the oil for your flat tappet motor has zinc in it

Can I use this? My engine is rather old. Some say you can use a higher viscosity.

 

[Scott06]

Can I use this? My engine is rather old. Some say you can use a higher viscosity.View attachment 377519

Yes also a lot of folks will use Rotella conventional oil 15W40. Yes its diesel oil but a lot of folks use it for marine applications and older flat tappet cam engines. It is also pretty inexpensive vs these oils marketed towards classic car crowd.

When I replaced my engine with w new long block in 2016 Michigan Motorz requested I do the break in with Rotella.

 

[Scott Danforth]

Can I use this? My engine is rather old. Some say you can use a higher viscosity.View attachment 377519

You need zinc with a flat tappet cam. you can use this over-priced oil. I run Rotella T4 15W-40 Diesel oil myself

 

[stresspoint]

yes you can use that castrol 20w50, in fact i only use Valvoline regular mineral 20w50 oil in all my boat motors including my 500hp vortec 5.7,
i use it in my 4.3 and it seems to have stable oil pressure through out the RPM range
when i was running high output moded V6 4 stroke out boards i used the same oil , those things thrived on it , always on changes the oil was as clean as the day it was put in there.