oil with zinc for 1977 350 chevy engine for 24'searay

[tinkertoy]

I was told many years ago that you should use straight weight oil because
when using a multi weight (IE) 15-40 the average marine engine does not reach 180 degrees (not including closed systems) therefore you are using only the 15 weight portion of the oil, the 40 weight portion only becomes effective at or over 180 degrees,dont know if this is true but it seems to make sence.
I use castrol straight 50 weight racing oil in my boat. I also agree that
Shell Rotella is probably the best, I use it in my trucks,front end loaders,Ect.
I am also a believer in the lucas products, I had a 1975 Lyman and the rear main was leaking and the lucas formula definatly worked. And I am not a big
believer of fix it in a can. lol Good fishing to all. Tinkertoy (john)

[wakina]

Here is how the viscosity rating is explained. The following is from the link that I have provided at the end of the quote. Also the operating temp of the engine is measured by water temperature and not oil temperature. Oil temps are almost always higher than the water(cooling) temp as oil is only cooled from the heat exchange effect created by the water cooled system. That is unless there is an oil cooler installed.

Quote " Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Your engine needs oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil. This is the best of both worlds and is accomplished by using special additives to increase viscosity with increase temperature. " Unquote

http://www.autoeducation.com/autoshop101/oil-change.htm

I hope this helps clear up some of the mystery that seems to surround what the viscosity numbers mean and when they are achieved as engine oil temps rise. 10w40 oil would have a rating of 10 at zero degrees and 40 at 210 degrees! The viscosity of the multi grade oil rises with the temperature of the oil and increases the oils wear protection.

[tinkertoy]

Wakina. Your explanation makes a hell of a lot more sence than what I was told, I was given that info many many years ago and I wondered about that then. Thanks for the GOOD info. Tinkertoy.