Oil for I/o?

[BALLS DEEP]

I have a mercruiser 5.7 liter 350. I thought last year I used an sae 30 weight oil. I bought some shell rotella this morning, got it home and realized it was heavy duty diesel oil. Is this ok or do I need something different?

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[finsntins]

i dont think you want to use that,i would think you would want 5w30,not an i/o guy,but i am a chevy guy and thats what i have always used.

[Hooked on Kings]

I use Mercruiser 25 - 40 synthetic blend, I think it holds up better to the long hours of trolling all day. I have also used Quicksilver blend as well, both work well.

[rlconverse]

I talked to an engine builder he told me that the new spec on oil is that they removed the zinc from the oil, hes seen alot of cams eaten up from the lack of it. He suggested that i run a zinc additive in all flat tapper/ non roller cam engines. Lucas oil products make a zinc additive

[Has Been]

My)MC  5.0 chevy says straight  30 wt . Would think 5.7 would be the same.

[JakeyBaby]

Depending on the year.... you dont want to run 5w. My 87' I run I0w-30.

[poverty stricken II]

Dont run the diesel oil. Your engine will not make it through the spring.

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[ontherise]

What does the manufacturer recommend?

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[BALLS DEEP]

The engine is an 89

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[Glenn -Brazee]

Like others have replied, always check the owners manual. I believe it called for SAE 30wt back then. Now with the newer blends available, Quicksilver 4-Cycle 25W-40 Marine engine oil is recommended by Mercruiser site and mechanics. I wouldn't use anything other than specified. Hope this helps.

[TileMan Dan]

GM s are usually straight 30 weight I have a 5.7 in mine repowered last year and running synthetic now

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[hooknup]

SAE30

[machzrcr]

Straight 30 dont want it to thin out when engine is warm and low rpm.

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[Knotlost]

This is what you want... 

10W-30 Synthetic Formula 4-Stroke Marine Oil : Case of (12) quart bottles

 

Its Amsoil, and its made for the boat. I run it and if you need to get some PM me I will get it for you at Dealers cost to your door.

 

PK

[Xxx]

This is what you want... 

10W-30 Synthetic Formula 4-Stroke Marine Oil : Case of (12) quart bottles

 

Its Amsoil, and its made for the boat. I run it and if you need to get some PM me I will get it for you at Dealers cost to your door.

 

PK

My uncle builds dirt modified race car engines and he repowered my 350 merc. punched 30 over with all the modern goodies as it was a 1982 flat tappet and now a full roller motor 2 years ago and what PKomrowski said is what he recommended I use      it's not cheap but neither are new motors!!

[Tim Bromund]

My Mercruiser Manual Recommends 25W-40, so that's what I have always used.

[FleetTracker]

Lots of folks are running the Rotella and I've heard great things. Some mechanics are recommending it. I Also have a 5.7L Merc 350mag and am considering going with it. Has anyone else been running Rotella T 15-40?

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Edited April 8, 2014 by FleetTracker

[bout time]

My Mercruiser Manual Recommends 25W-40, so that's what I have always used.

Same here .....

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[Chas0218]

Diesel oil is better if it has flat tappet cam. It will make no difference whether it says diesel or not long as it is the correct weight.  Diesel motor oil just has more additives to help eliminate premature lifter failure. Your motor will be fine long as it is the correct weight.

[pete277]

I just looked in my 88' Mercruiser manual for  my 5.7 I/O and it recommends a good grade SAE 40w, SF  detergent automotive straight weight oil for an ambient temperature above 50 deg.F.    and a 30W,SF  for temps between 32 deg and 50 deg F.

[dick black]

no no no shell rotella has a much higher ash content check owners manual for correct oil applications

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[lrg355]

I have looked into oils as part of my job. The major manufacturers of marine engines usually recommend straight weight oil such as SAE 30. This is because the multi viscosity oil like 10w-30 is loaded with additives to make it act like a 10w oil in cold weather and 30w in warm weather. the problem with that is the additives are the major cause of "sludge" we all see in the engine. Since a auto engine converted to marine use usually is only run in temps well above freezing, there is theoretically no need for additive loaded multi-viscosity oil. I just wish someone would make a single weight, readily available synthetic.

[lrg355]

Also, the W in 10w-30 stands for Winter.  It is the viscosity at 0 degrees F.  The second number (30) is the viscosity at 210 degrees F. 

Plenty of additives to make that happen.

[Chas0218]

I have looked into oils as part of my job. The major manufacturers of marine engines usually recommend straight weight oil such as SAE 30. This is because the multi viscosity oil like 10w-30 is loaded with additives to make it act like a 10w oil in cold weather and 30w in warm weather. the problem with that is the additives are the major cause of "sludge" we all see in the engine. Since a auto engine converted to marine use usually is only run in temps well above freezing, there is theoretically no need for additive loaded multi-viscosity oil. I just wish someone would make a single weight, readily available synthetic.

 

Actually diesel oil has more detergents than normal "gasoline" oil meaning less sludge than a gasoline motor. Diesels produce more soot and contaminants than a gasoline engine making it more important to have more detergents.  Diesel oil utilizes more phosphorous, Zinc and magnesium than gasoline oils. This is because diesel motors have flat tappet cams.  These style cams have a flat metal surface that rides against a flat metal cam lobe without the additives the cam and lifter will fail prematurely.  That is also the reason why older cars/boats run diesel oils.  You can also accomplish the same by running one of those aftermarket additives in gasoline oil.  I don't like the aftermarket additives they don't do as good of a job as the motor oils that have it in the formula from the factory.

[FleetTracker]

Got the scoop... 4+ years ago Shell Rotella would have been an excellent choice and many major marinas and mechanics recommended it. What most do not realize is about 4 years ago, Quaker State bought the Shell Rotella product line and maintained the brand without change... Well, to the name. They DID change the content of the oil and removed the zinc additive from it. Shell Rotella is now not a recommended oil for use in marine gas engines and has largely been removed from many marinas who used to use it. I'll go with the OEM quicksilver 25w40 oil. Still has the additives.

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