Do larger engines require heavier oil. A friend of mine just bought a '88 merc 3.0 i/o boat and on the oil fill cap it says 10w30. I would have recommended straight 30w if i wouldn't have seen this. Also the guys with the 502's seem to always use straight 40w. My 5.0 says 20w-50 on the engine and 40w for the 454. But i use 30w and have great pressures. Why the call for 10w30 with the merc 3.0?
larger engines = heavier oil?
- Thread starter JonS
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The 502s are known for burning oil, and thicker oil helps reduce that.
FYI, contemporary 3.0L I4 Merc calls for 25W40 with streight 30, 40 or 20W50 being less desirable alternatives. I doubt if the engine has changed a lot since (except for carburator or ignition).
Like jack said above, oils and knowledge have improved since 88. I'd definently go with a thicker oil like a straight 40 weight. Mercruiser does mention the less VI's, the better. But, I don't know how their Quicksilver brand 25-40 can't have a buttload of VI's in it for that big of a spread. On the 3.0's, I'd go with a 30 or 40 st. weight, 4.3 and above...nothing less than a 40 weight. As the engine get's older and more hours on it, I'd go with a 50 weight.
These are engines that are based on Automotive engines. Don't go by the info on the cap, that is the same cap that they use for cars. the old Mercs had these caps on them, and I expect that they changed this at some point.
I don't think engine size or the clearance or "tolerance" as some people refer to has anything to do with the engine oil grade.
How hot the engine oil operates at, the valvetrain loading, and how well the engine is designed should dictate the viscosity of the lubricant.
The Chev big blocks are known as valvetrain eaters for several reasons, not to mention their crank and rod oiling problems, and their poor 1.53 con-rod ratio.
I'm sure that a tall deck 427 BBC with a small journal Dodge 426 Hemi rod, a good oil pump, and a rollerized valvetrain could easily run with 5W20 in the crankcase.
On the other hand a little 3.0 working its @$$ off in a 22 foot boat could have engine oil temperatures far above the big engines.
4500 HP locomotive engines use either 20W40 or SAE 40 in the 2-strokes. If the bigger the motor the thicker the oil theory held true, 30,000HP ship engines also would use engine oils far heavier than an SAE 30 or 40, but they don't.
How hot the engine oil operates at, the valvetrain loading, and how well the engine is designed should dictate the viscosity of the lubricant.
The Chev big blocks are known as valvetrain eaters for several reasons, not to mention their crank and rod oiling problems, and their poor 1.53 con-rod ratio.
I'm sure that a tall deck 427 BBC with a small journal Dodge 426 Hemi rod, a good oil pump, and a rollerized valvetrain could easily run with 5W20 in the crankcase.
On the other hand a little 3.0 working its @$$ off in a 22 foot boat could have engine oil temperatures far above the big engines.
4500 HP locomotive engines use either 20W40 or SAE 40 in the 2-strokes. If the bigger the motor the thicker the oil theory held true, 30,000HP ship engines also would use engine oils far heavier than an SAE 30 or 40, but they don't.
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