Best oil and filter for '87 Mercruiser 5.7L GM?

[Will 55]

Have been running a 5.7 Merc in an '87 230WE on Mobile 1 15w 50 for 3 decades. Was thinking about changing over to Amsoil 25W 40 Marine. Any recommendations? (I've heard Amsoil is the best and i use it in my tow vehicle). Maybe I shouldn't change the type oil that I've been using for so long?

 

[Maggieiscrazy]

Have been running a 5.7 Merc in an '87 230WE on Mobile 1 20w 50 for 3 decades. Was thinking about changing over to Amsoil 25W 40 Marine. Any recommendations? (I've heard Amsoil is the best and i use it in my tow vehicle). Maybe I shouldn't change the type oil that I've been using for so long?

Why not use Quicksilver oil and filter? It’s what Mercruiser recommends and it’s relatively inexpensive at Walmart. I think Amsoil is way overrated.

 

[paulswagelock]

Amsoil is a boutique oil, pricey, and just not going to gain you anything. Why not keep doing what has served you well?

 

[Lazy Daze]

I'll just add... there is no such thing as a "best" oil. It's all personal preference. Do what feels best for you and your pocket book. The reality is, especially with a 30+ year old boat that uses an engine designed even earlier than that... pretty much ANY half-way decent marine oil is going to be MORE than adequate. Don't think too much on this one - go boating, instead!

 

[Will 55]

I guess I've been swayed by Amsoil hype so much that I joined their preferred customer club. I guess it's not much different or better than the Mobile 1 I've been using for 30 yrs. Funny how marketing works.

Amsoil is a boutique oil, pricey, and just not going to gain you anything. Why not keep doing what has served you well?

 

[hottoddie]

Just make sure the oil has the ZDDP additive that flat tappet engines need to prevent camshaft/lifter failure.

 

[Will 55]

Actually the oil I have been using is Mobil 1 15w-50. And the product sheet states:

"Boosted, higher viscosity, advanced full synthetic formula designed for performance vehicles. For HT/HS applications, racing and flat tappet applications."
https://www.mobil.com/lubricants/-/media/project/wep/mobil/mobil-row-us-1/files/mobil-1-product-guide-rev-31.pdf

I probably lucked out when I chose this oil. I guess I'll stay with it.

 

[Red Wing Willy]

Actually the oil I have been using is Mobil 1 15w-50. And the product sheet states:

"Boosted, higher viscosity, advanced full synthetic formula designed for performance vehicles. For HT/HS applications, racing and flat tappet applications."
https://www.mobil.com/lubricants/-/media/project/wep/mobil/mobil-row-us-1/files/mobil-1-product-guide-rev-31.pdf

I probably lucked out when I chose this oil. I guess I'll stay with it.

Will, funny my name is William and I was born in 1955..hmm. I have twin 1987 5.7 mercruisers and these engines do have flat tappet cams as stated above. You did "luck out" as the 15w-50 Mobil 1 is one of only 3 of the Mobil 1 variations that have the correct level of ZDDP for our engines (Optimum is 1200 PPM - Parts per Million). Mobil 1 markets 37 different variations of that oil (Listed in your link)

. Starting around 1994 oil manufacturers started reducing the level of ZDDP (which is Zinc + Phosphorous as an anti-wear additive) because it was found to damage Catalytic Converters in cars. Merc and Crusader changed their engines to Roller Cams starting in 1996, and the ZDDP is not critical to have for these later engines.

I use T6 Rotella 15w-40 which also has 1200 PPM and is the exact viscosity Mercruiser recommends. (Note, the original manuals stated straight 40 weight, but they changed to 15w-40 later and Merc recommended this for the earlier engines, too). I believe the Amsoil stuff is great, but overpriced and not necessarily better for our boats.

 

[Will 55]

Good to know, and yes, I did luck out. Have been using Mobile 1 15-50 for 30 yrs straight, and the engine runs like new.

 

[Skybolt]

I have always run Shell Rotella. Straight 40 in my diesels but 15/40 in my crusaders. Had my crusaders surveyed with 2500 hours on them and still had 130 (454 lower then 350) average psi in each cylinder, like new. New owner was very happy.

 

[HardHead]

Have been running a 5.7 Merc in an '87 230WE on Mobile 1 15w 50 for 3 decades. Was thinking about changing over to Amsoil 25W 40 Marine. Any recommendations? (I've heard Amsoil is the best and i use it in my tow vehicle). Maybe I shouldn't change the type oil that I've been using for so long?

If it's been running well for 30 yrs, don't change anything....
"If it ain't broke don't fix it"