Oil lubricants and the common man

Marine Mechanics need to have an overall understanding of oil products. Always, refer to engine and/or owners manuals for specific information, but you should be aware of the basic, yet significant, differences in the oils and lubricants used today.

Two stroke gasoline engine

Two stroke gasoline engine oils are formulated with the following additives:
* Detergents to neutralize acids formed during combustion
* Dispersants to hold contaminants in suspension and off the metal surfaces of the engine
* Anti-wear agents
* Rust and corrosion inhibitors
* Polymers to reduce exhaust smoke and exhaust system blocking.

Major performance requirements of two-stroke gasoline engine oils include:
* Protection against ring sticking
* Protection against exhaust system blockage
* Protection against piston and cylinder scuffing
* Protection against deposit-induced pre-ignition
* Rust prevention
* Biodegradability

There are two designations that a two-stroke gasoline engine oil may be classified as:
* American Petroleum Institute "TC"
* National Marine Manufacturers Association "TC-W3"

TC-W3 quality oils are preferred by most outboard engines and personal watercraft. Some personal watercraft manufacturers, (Bombardier for example), specify not to use TC-W3 quality oils on some of their engines.

TC (low-ash) and TC-W3 (ash-less) oils primary difference is in ash content. Ash content is the non-combustible portion of a lubricating oil. Many of the additives found in fully-formulated lubricating oils contain metallic, non-combustible derivatives, such as barium, calcium and magnesium. Ash-less oils must be formulated without metallic or noncombustible additives.

In North America, four-stroke gasoline and two- and four-stroke diesel engine oils are all classified by the American Petroleum Institute (API). The engine manufacturers will specify the API service category and Society of Automotive Engineers (SAE) viscosity grade that they prefer based on the ambient operating temperatures and the quality of oil required for the design of the engine.

Four-stroke gasoline engine

Four-stroke gasoline engine API service categories always begin with the letter S.
Diesel engines begin with the letter C.
These letters stand for "Service" and "Commercial" sometimes refereed to as... "Spark Ignition" and "Compression Ignition".

There are seven current base API service categories:
* API SJ is for most four-stroke gasoline engines. (Current automotive API is SM which replaced the SL category)
* API CF-2 is for many two-stroke diesel engines.
* API CF, CF-4 and CG4 for many four-stroke diesel engines.

The requirements of four-stroke gasoline and two- and four-stroke diesel engines, motor oils are formulated with the following additives:
* Anti-foaming agents
* Oxidation inhibitors
* Corrosion inhibitors
* Rust inhibitors
* Anti-wear and anti-scuff agents
* Detergents to neutralize acids formed during combustion  (non-detergent oil is required in some applications)
* Dispersants to hold contaminants in suspension and off the metal surfaces of the engine
* Polymers to improve the ability of the oil performance in cold temperatures and over a wide range of temperatures.

It's important to note that the amount and type of additives varies by manufacturer and intended usage. For example: Valvoline has a very high zinc/phosphorus content in it's VR1 & "Not Street Legal" engine oil "which provides extreme wear protection (including flat tappet applications) combined with additional friction modifiers to help deliver maximum horsepower". Most marine engines benefit from this type of formulation. Unfortunately, zinc/phosphorus additives has a long term detrimental effect on catalytic converters. So, you should not use this type of oil in marine engines that have catalytic converters. 

Volvo Penta and Mercruiser both have modified their OEM branded engine oils to conform with the current marine engine packages that they sell, which have catalytic converters. They say these oils will work with their older non-catalytic marine engines however, they do not state whether engine durability is affected. Sierra Marine and other generic suppliers still sell their oils for either catalytic & non-catalytic marine engine type.

A majority of 4 stroke inboard marine engines run best on a straight weight engine oil. 30W and 40W being the most common. Marine grade multi-viscosity oils are also available. (Note the phrase "Marine grade") The most popular is the 25W-40 oil available in both mineral and synthetic base. These work well for general purpose marine engines. However, multi-viscosity oils are not typically recommended for high performance marine engines and those with flat tappet.  Also, adding an oil additive similar to Johnson LL5 to mineral base oil used in a high performance engine is strongly recommended.

Several of the latest 4 stroke inboard and outboard engines have started to come from the engine manufacturer with blended and full synthetic multi-viscosity engine oils. These oils are specifically blended for either 4 stroke inboard or 4 stroke outboard engines used in the marine environment. Substituting probably won't instantaneously destroy your engine however, overall engine life and performance will be better if you use the oils designed for your application.

Special Purpose lubricants

There are three API service categories for gear oils:
* API GL-1
* API GL-4
* API GL-5
Most outboard and stern drive manufacturers recommend API GL5 gear oils for their lower units. API GL-5 gear lubricants are for both mechanical shift units calling for Type B gear oil and electrical shift mechanisms calling for Type C gear oil. (only the viscosity value will be different for each application)

Recent additions and modifications to gear case lubricants have come from several manufacturers. Primarily, these are blended gear oils where both mineral base and synthetic base lubricants are blended together. Since synthetic base lubricants do not mix well with potential moisture; the marine industry primarily recommends these blended gear oils be used in their products. There are a few model exceptions that have gone to full synthetic recommendation. 

Transmission fluid needs to have excellent oxidative stability and anti-foaming characteristics, and must be able to perform over a wide range of temperatures. Dexron(r) III & Mercon(r) formulations meet the requirements of Type A, Dexron(r), Dexron(r) II, Dexron(r) II-E and Mercon(r) ATFs. Current Dexron(r) III & Mercon(r) and Spirax (S3 ATF MD3) formulations are also generally suitable as Allison C2, C3 or C4 type fluids.

On the other hand, Type F ATF has a different frictional property than Dexron(r) III, Mercon(r) and the new Spirax (S3 ATF MD3) from Shell oil Company. 

(Note: some marine transmissions use regular motor oil)

Always refer to the manual for exact specifications but as you can see, standards exist to create a uniform atmosphere for compatibility in lubricants. This should make it easier to choose one brand over another. Also note that every "generic brand" lubricant has to comply with the same standards as the "brand name" lubricant to carry a specific classification. (and there are only a hand-full or so of lubricant manufacturers as compared to the numerous "brand names" they manufacture.)

There is a case to be made for "product specific" lubricants that are distributed by engine manufactures for their product. These engine manufacturers can specify changes or additions to a specific type of oil that would carry that engine manufacturers "private label". Not all lubricants in the same category are formulated the same. Ask your supplier or rep some cold hard questions. Also, ask your customer if he'd rather pay the premium for the OEM packaged product.
(See an experiment run by Mercury a few years back.)

The bottom line is that each oil has to pass the test for it's category, but the question is: "How well, did they pass?" and "What did they put into the oil, so it would pass? " There in lies the difference.....

Additional reading: Oil FAQ's by Valvoline. [opens in new tab/window]



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