1993 Mercruiser 350 Ski Magnum carbed oil type

Scott06

Scott06

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Chris1956 said:
Scott, Is your engine made by Michigan Motors?

Now my knowledge is dated, but my MerCruiser called for SAE-30 or SAE-40 or the Quicksilver 25W-40. I have seen newer four cycle marine motors that specified an FC-W oil, but never diesel motor oil.

Run what you want, but please update us on the failure cause.
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Stop with drama, they sell Marine power long blocks (new GM marine) as well as merc bobtails and rebuilds. Doubt they are recommending oil that would cause a warranty issue or lessen engine life. Also doubt that the seller (merc) would recommend anything that doesn't have their label.

Failure cause? there is no failure I'm on my tenth season of heavy watersports use. Typical use is our kids plus some friends - so 6-7 people towing a skier or wakeboarder.

I bought a handyman's special (non running) where PO cracked the block...

Point being - for 99% of recreational use there are plenty of oils that will work just fine. Most of the failure mechanism is neglect either poor winterizing, rotted exhaust manifolds, or not changing the oil or checking level. Stay away from the 0W-, 5W-, 10W- and you will be fine
 
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Scott Danforth

Scott Danforth

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Yes, engines in the late 80s and early 90s called for straight weight oil.....

Then oil technology got better and the OEMs switched to 20w40 and 20w50..... Then zinc levels dropped as motor technology advanced

Don't over think it. The 15w-40 diesel oil is pretty much perfect for a boat motor with a flat tappet cam
 
C

Chris1956

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OK, I am frustrated. Why is it that you cannot use what the OEM recommended? Is it cost? Is it genital size? Is it some version of "they don't want you to know"?

Just wondering?
 
Scott06

Scott06

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Chris1956 said:
OK, I am frustrated. Why is it that you cannot use what the OEM recommended? Is it cost? Is it genital size? Is it some version of "they don't want you to know"?

Just wondering?
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If genital size is frustrating you that is for a different forum...

Above I said ask two guys what oil to use and you will get three different answers, thanks for proving my point.

Guy asked what oils he can use , relayed 40 years of experience and options... never said its the only way, just this way works. Wondering why- read the thread, but don't make this a chit show for no reason.
 
Lou C

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The reality is, it may take years for a possible failure to manifest, and other causes like bad exhaust, overheats, etc may cause a real failure before a theoretical failure due to oil choice.
The only way to know, is to do oil analyses, consistently and compare wear metals and the physical properties of the motor oil.
I found that the Merc 25/40 stayed in grade as well, as the straight Delo 30 I used to use when I first got this boat
The best results were found with the Merc Syn Blend 25/50 which is probably the best oil they sell, very expensive but some might think it's worth it.
 
Lou C

Lou C

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BTW the only automotive engine I have with a flat tappet cam is my '98 Jeep Grand Cheroke with 4.0 liter six, it is quiet as can be with a steady diet of Valvoline MaxLife 10w/30. 182,000 miles. And this oil is not high in zinc, IIRC about 860 PPM
On the other hand the Merc Syn Blend 25/50 is a good bit higher than the Merc 25/40, it has about 1300 ppm zinc
 
Scott Danforth

Scott Danforth

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Chris1956 said:
OK, I am frustrated. Why is it that you cannot use what the OEM recommended? Is it cost? Is it genital size? Is it some version of "they don't want you to know"?

Just wondering?
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You're one of those aren't you.

You're short circuiting.....

Someone who is so enamored with a recommendation made 33 years ago for a motor that is now obsolete by today's standards for an obsolete oil spec that was state of art 35-40 years ago that you short circuit if some makes a suggestion on a better product .

Straight SAE30 with zinc is fine. It is now near impossible to find with enough zinc to run a lawnmower much less than a flat tappet tow boat motor unless you buy break-in oil

SAE 30 high zinc is about $25 a 5-quart container

BTW..... Rotella T4 is also now obsolete, but it's attainable at $15 per 5-quart container and has the level of zinc needed
 
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Chris1956

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Scott, I am simply wondering aloud why people do not run the oil specified for their motors. It seems pretty easy to me.
 
jimmbo

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Scott Danforth said:
Yes, engines in the late 80s and early 90s called for straight weight oil.....

Then oil technology got better and the OEMs switched to 20w40 and 20w50..... Then zinc levels dropped as motor technology advanced
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My 2002 5.7 VP, the Manual, said SAE 30 Synthetic, nowhere in the Manual did Volvo spec a Multigrade.
 
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Pmt133

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Years ago there were a series of tests run that were coordinated with comp cams to trend flat tappet wear. They used a bunch of off the shelf oils to measure wear on the lobes in microns and from what I recall, the diesel oils always tended to perform worse. Now was it enough to cause alarm? No since we're talking a couple microns at most... But enough to raise an eyebrow at. Early 00s API motor oils were indeed horrible for flat tappet engines. With modern oils designed with DI in mind however, they have a better additive package despite lower zinc and protect nearly as well as any boutique oil on the market aimed at working in an older vehicle...

What I think? You all are over thinking it. But that's just me. Just another oil thread as usual. Pretty much anything in that sump is going to be more than fine.
 
matt167

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If you use the oil specified for the engine it’ll be the wrong oil. Look at the oil cap. It’ll probably say 10w30 or 5w30 which would be wrong.
Oil matters less than people make it to be. You can use OEM oil, 15w40 diesel oil or many different 20w50 oils provided they have enough zinc. Change it once a year or every 100 hours and it won’t matter
 
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