Marine Engine Lubricants

Items 1-30 of 63

Set Descending Direction
per page

Marine Engine Lubricants How-Tos

Intro to Lubrication

Dan Watson, of Marine Technician Today Magazine, discusses the importance of lubrication for your boat. By Dan Watson with Marine Technician Today Magazine; Spring 2014

Simply stated, there is a direct connection between lubrication and the health and life of your engines and outdrives. Manufacturers have done their part by manufacturing these marvelous machines; each owner is solely responsible for their maintenance. As a Certified Lubrication Specialist (CLS), certified by the Society of Tribologist and Lubrication Engineers (STLE), I cringe at the misleading advertising, misinformation and lack of lubrication education for both consumers and service professionals. In this continuing series, I seek to provide factual information on lubrication to allow readers to rise above all the advertising hype and half-truths in order to make informed decisions when selecting lubricants - engine oils, two cycle oils, and gear lubes - for their marine applications. With this goal in mind, I intend to educate, not indoctrinate. In fact, the information in these columns will equip you to see through the attempts at indoctrination that surround us.

I want to begin with some fundamentals of lubrication and, in subsequent editions of Marine Technician Today, progress through lubricant formulation and applications.

So come along for the ride and be sure to jot down questions as you read. You will always find my email address at the end of the article, and I will be glad to answer your questions.

Fundamentals of Lubrication

Why Lubricate? Millions, no billions of dollars are spent annually lubricating every moving part in virtually every machine in operation worldwide. The short answer is that lubrication overcomes friction. Friction is not a complicated phenomenon, but it is important to correctly grasp this simple concept. When two surfaces slide or roll in contact with each other, friction is the force that resists that motion. It is important to remember that motion is required in order for friction to occur.

There are several factors that affect the level of friction between the moving surfaces. I list these in no specific order or level of magnitude. - Surface finish: relative smoothness or roughness - Type of motion: rolling versus sliding - Load: amount of pressure pushing the surfaces together - Speed: rate of relative motion - Lubricant: base fluid, viscosity and additives - Temperature (affects the condition of the surfaces and the viscosity of the lubricating film)

Surface Furnish: Asperities

Viewing the surface of metal with amicroscope reveals extremely small jagged peaks called asperities (Figure Two). There are continuous peaks and valleys of metal almost like microscopic mountain ranges. It is impossible to machine the metal surface fine enough to remove these asperities. Obviously, separating these asperities is paramount to reducing friction and resulting wear. Reviewing the factors listed that affect friction, it is apparent that lubrication is the factor most useful for limiting friction. The motion is set by application and the load and speed will be related to the work application. Temperature is usually a range determined again by the application. Now since lubrication is our vehicle for limiting friction and wear, it is important to identify the types, or regimes as they are called, of lubrication that are available and in which applications each regime comes into play.

Boat Motor Oil Formulation

Formulation of motor oil as explained by Dan Watson of Marine Technician Today Magazine. By Dan Watson of Marine Technician Today Magazine, Summer 2014

Understanding how to prevent friction is the first step in engineering a lubricant to deal with friction. Friction maybe the primary detriment that the lubricant is designed to combat but it is only one of many the oil will have to provide a solution for. The formulation of motor oils and why we put all those additives in lubricating oil is a basic question we have to address to understand lubricating oil. Before we get into the formulations, we better take a look at the functions of motor oil. If we understand what oil is doing, then we can better understand why we choose certain base stocks and additives.

Motor oil must perform the following functions:

  • Lubricate engine parts in order to prevent wear
  • Reduce friction and improve fuel economy
  • Maintain clean engine components
  • Prevent rust and corrosion
  • Minimize engine deposits
  • Provide engine cooling
  • Aid in engine starting
  • Provide ring seal for better combustion pressure

Each of these functions is vital to optimum performance as well as to the durability of the internal combustion engine. Motor oils are complex lubricating fluids carefully formulated to perform all of these functions. Motor oil is composed of base stocks and additives. The base stocks are either petroleum or synthetic and the additives are chemicals designed to satisfy the functions listed above, depending on engine type and duty.

Base Stocks

Base stocks are derived from two sources: petroleum (crude oil) and synthetics. Within these sources there are several levels of quality. The old saying Oil is Oil is simply not true and potentially misleading. All oils are classified into groups with the lowest quality oils forming Group I and the highest quality forming Group VI (Group VI oil is not used in internal combustion engines). The amount of refining (purification) and the Viscosity Index determines where the oil falls on the scale. Presently almost all petroleum oils are being made from Group II oils. This is a significant change since, not so very long ago, most petro's were Group I. Some petroleum oils are made from partially hydrocracked Group II oils. Synthetic motor oils come from Group III, IV and V oils. In a later issue, I will go into greater detail on the specific differences between the various groups of base oils. For now, I just want you to know that there are levels of quality in base stocks.

After a base stock is chosen, then additives (chemicals) are selected to provide:

  • Anti-wear
  • Anti-foam
  • Anti-oxidation
  • Detergency and dispersancy
  • Neutralize acid
  • Prevent corrosion and
  • Maintain viscosity

To understand motor oil, it's necessary to take a closer look at base stock properties and these additives and how they relate to the vital functions of motor oil.


Viscosity refers to the resistance-to-flow of the oil and is the most critical property of a lubricating oil. Viscosity varies with temperature, being greater at colder temperatures and less at warmer temperatures; in other words, it is thicker when cold and thinner when hot. If motor oils are too viscous (thick) at engine start they make starting the engine more difficult. This is especially true of diesels. Conversely, if the oil thins too much at high temperatures, it does not provide adequate wear protection. The measure of an oil's change in viscosity with respect to temperature is referred to as Viscosity Index (VI). The higher the VI rating, the more stable an oil's viscosity is with regard to changes in temperature, which means an oil will thicken less at colder temperatures and will thin less at hotter temperatures. Additives, referred to as VI Improvers are used to increase the VI, making the oil less reactive to temperature changes. Petroleum oils require significantly more VI Improvers than synthetic oils because synthetics inherently possess a higher VI.


The viscosity of an oil must not be so high at cold temperatures that it inhibits starting or fails to flow to the critical lubricating points in the engine. Pour Point, a term helpful in determining an oil's ability to avoid these occurrences, is defined as the lowest temperature at which a fluid will flow. Petroleum oils naturally contain waxes that crystallize at low temperatures causing the oil to rapidly thicken and lose its ability to flow. Pour Point Depressants are chemicals that prevent wax crystals from joining together and thickening the oil. These chemicals are added to all petroleum oils with winter ratings, which is signified by a W as in 10W-30. Synthetic oils are wax free with very low pour points and so do not require pour point depressants.


Motor oil removes approximately 40% of the engine heat. The radiator system removes 60% but the entire lower portion of the engine is cooled only by oil. Engine lubrication could easily be accomplished with much less oil in the crankcase but additional volume is necessary to provide oil flow for heat removal.


A principal function of lubricating oil is to prevent wear. Anti-wear additives are designed to bond to the surfaces of the metal to protect the surfaces when the lubricating film of oil cannot maintain separation of the moving surfaces. Made usually from zinc and phosphorus compounds, these anti-wear additives act as soft, solid lubricants that prevent steel-to-steel contact. Anti-wear additives create a protective film on the moving parts and are critical for protection during start up and during heavy loads.


Oxygen is an extremely chemically reactive element and when it reacts with oil it produces sludge and varnish deposits and causes oil thickening. When oil operates at elevated temperatures, oxidation is accelerated. Compounds formed by the byproducts of combustion and oxidized oil form acids that contribute to rust and corrosion. This corrosion process is more critical in diesel engines than gasoline. Oxidation Inhibitors are added to oil to reduce oxidation. Petroleum oils react highly with oxygen, whereas synthetics are nearly inert, and react very little with oxygen. Total Base Number Total Base Number (TBN) refers to an oil's ability to neutralize acid. TBN is measured on a scale of 1 to 13: the higher the number the greater the capacity to neutralize acids. A high TBN is required for extended drain interval oils and most diesel oils should have a TBN between 8 and 12.


The combustion process by-products form sludge and varnish deposits in the engine. Deposits can cause hot spots in the engine, affecting its performance and fuel economy. Detergents are added to aid in removing these deposits.


Combustion by-products, such as carbon, are maintained in solution by dispersants, reducing deposits. Dispersants are designed to keep the byproducts in the oil until the filtration system can remove them. Dispersants and Detergents work hand in hand to keep the engine clean.


Imagine a blender whipping your motor oil and you will get a pretty good picture of how the oil is whipped by the rapidly moving parts in the engine. As the oil is whipped, it traps air. The resulting foam has very poor lubricating properties. Chemical additives such as silicone are added in near trace amounts to reduce foaming. The effect of these anti-foaming additives is to weaken the air bubbles, allowing them to collapse more quickly, thus reducing the amount of foaming that occurs.


Seals come in various sizes, shapes and materials. It is necessary for motor oils to not only be compatible with the materials, but to nourish the seals. Seals should not degrade, dissolve, crack or shrink. As an additional benefit, some, but certainly not all, oils even cause a little swelling of the seal.


Marine engines operate in a continuously wet high humidity environment and it is essential to have chemical rust and corrosion inhibitors added for protection. Standard automotive engine oils are not designed for the marine environment and will not provide adequate protection. Chemical rust inhibitors attach to the surface of the metal and prevent water and oxygen from getting to the metal surface preventing oxidation.

Copyright © 2023 BOATING INVESTMENT GROUP LLC., - IBOATS. All rights reserved.