Oil Type for 5.7 ?-gctid370644

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Hi all, Well I am ready to service my Mercruiser 5.7 V8 engines and were intending to use Castrol Magnatec 10W-40, but have since been told that I should be using the GTX 15W-40, here I was thinking that it was better to use the more expensive superior product. I checked out the Magnatec for Zinc which it has to help reduce wear and not being a full synthetic, thought that it would be the bees knees, Can anyone advise which way I should go ?

[Chief_Alen Guru Find all posts View Profile Close Chief_Alen]

Whats posted on the engine ?

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Sorry not sure what you mean, Do you mean in the service manual ?

[tonyiiiafl Seasoned Member Find all posts View Profile Close tonyiiiafl]

I use mercury Quicksilver 25W40 in my VP (GM) 5.7

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tonyiiiafl wrote:
I use mercury Quicksilver 25W40 in my VP (GM) 5.7

Hey thanks.

[JimMc Guru Find all posts View Profile Close JimMc]

I too use the standard Mercury Quicksilver oil.

It's designed for use in the Merc engine. I see no reason to not use it.

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Can anyone advise which way I should go ?

Shell Rotella 15w30. It's the oil that is most commonly used in commercial marine applications from ships to oil rigs. Inexpensive, and clearly works for heavily-used marine engines.

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I'm a fan of Rotella, but some of the GM marine engines need thicker oil. Especially the older ones. I"ve tried to troll with a V-8 using thinner oil and the oil pressure was too low. I picked up a lot of clattering in the drive train.