this was not written by me but a person on another forum called Wingnut, Thought this was a very interesting read.
Marine Oils Ain't Special
If you spend a lifetime talking to both the R&D guys and the organic chemists that support their efforts, you will get confirmation on all your suspicions. All the "factory approved" oils must come from somewhere. Merc and Volvo don't make oil. They give various suppliers a set of performance criteria and take the low bid. They then test the oil to make sure it meets their minimum standard and then have it stuck in their bottle. With cars it's easy. The spec is not very aggressive. Honda Certified Motor Oil is actually Mobil Clean 5000. The bottom of the food chain. Will it get you through the warranty? Sure. Can you do better? You bet. I don't know about you guys, but I like the fact that I just sold our Oldsmobile with 386,000 miles on it. You ain't going to get there on Mobil Clean 5000, but we did with Mobil-1.
The marine oil spec is a bit more aggressive, but the stuff still is not a blend to order product. It is a re-brand of an existing high performance motor oil. A blend to order product for that limited market would be $12/quart. Oil batches are either blended in an in-line blender where a row of meters proportionally blend the correct components at the rate of around 400 gallons per minute, or they are batch blended by hand in 9,000 gallon kettles at a very high cost premium. Some specialty lubes get made that way, but they cost a fortune.
The exposure that the marine industry has now is that all the newer generation car engines are going for increased fuel economy. This means lighter engine components and tighter tolerances which allow for the use of really thin oils. Heavy oils create parasitic drag wasting fuel and robbing horsepower. Also, reduced windage in the crankcase results from not having as much wetted surface oil throw-off to control. As the crank runs into the oil being thrown off the bearing surfaces, a rope effect occurs that drags the rotating assembly down. Tighter tolerances and thinner oils limit that effect. Marine engines cannot be manufactured to such tight tolerances as the higher component loads generate more thermal expansion. Build them that tight and they will seize up at operating temperature. Try to use light oils in them and they will beat themselves to death. Problem is that more and more oil compounder's are finding it necessary to eliminate their marine friendly oils as they are being forced to blend more flavors of the really thin specialized stuff, which is their bread and butter.
If you think Marine Oils are a "special secret formula", you're wrong. Will they get you to 1,000 hours on a gasoline engine? I've yet to see it but maybe if you change it often enough. I'll see you guys on the north side of the 1,000 hour club with my Mobil-1.
RECREATIONAL MARINE OILS...
I've followed the oil controversy for some time, and read the comments with interest, but it seems that most opinions are simple statements without any technical reference. I'm not a subject matter expert by any means, but have worked with some of the top Lube Chemists and Application Engineers in the business, and hopefully will be able to remove some of the apparent mystery surrounding "Marine Spec" oils.
First of all let's identify the fundamental differences between an automotive engine and a recreational marine application. Cars typically use a moderate percentage of their available horsepower to achieve cruising speed, then a much lower percentage to maintain said speed. A marine engine as we know is constantly loaded like a truck climbing a mountain and never reaching the top. As such, the marine engine combustion chamber temperatures are, on average, significantly higher than a comparably sized automotive engine. This alone creates a need for an extreme pressure component to be deposited on the cylinder walls to prevent compression ring and piston skirt scuffing. Marine engines are also jetted fatter on their fuel curve, and use a much colder spark plug. Control of ignition timing is also much more critical. The good news is that there is an inexhaustible supply of cooling water available to help with other related excess heat issues.
Secondly, engine oils have a propensity to attract moisture. With the boat sitting at the marina for weeks on end, marine oil will typically have an emulsifier added to help keep the oil in suspension until the next engine heat cycle drives out the moisture. If "moist" used oil is left in the crankcase say over the winter, it is not uncommon for acids to form which attack the lead/iridium coating on the engine main and rod bearings, leading to failure during the first cold start of the next season.
Let's set these two issues aside for now, and discuss the primary mission of motor oils. Most people think lubrication, and although lubricity is important, the primary purpose is to remove heat. To accomplish this, the oil must be in the right place at the right time and stay there until its mission is accomplished. Different oils achieve this utilizing different approaches.
Mineral based oils as pulled from the ground and refined have a multitude of different sized molecules. Quite simply, the medium sized ones do a pretty good job right out of the box. The big ones hang in there on a 90 degree plus day, but start to turn to tar as temperatures grow cold. As stated before, oil does no good if it's not where it's needed when it's needed. Cold start-up can be a problem with straight weight conventional oils for the first few seconds. To help with this, blenders add a pour depressant additive to the mix which tends to free up these big fat molecules as the temperatures fall.
The small molecules do not have a low pour point issue and will flow quite well at colder temperatures; however they have a nasty habit of vaporizing out the exhaust when temperatures climb. Another additive known as a viscosity improver attaches to these guys, and helps them to thicken as the temperature goes up. This is how 20W-50 oil can act as a 20 weight in winter and a 50 weight as temperatures elevate.
Lastly, in an extreme pressure application such as the cylinder wall to piston skirt scuffing phenomena common to marine engines, a blender will utilize an extreme pressure additive to negate this exposure. These materials, typically heavy metals, will deposit themselves into the tiny scratches in the cylinders and pistons providing a barrier of dry lubricant which stays in place until the carrier oil has an opportunity to deposit a new batch during the next splash cycle. These compounds can be moly-lithium-disulfide, zinc, graphite, lead, iso-sulfinates, and iso-calsinates (sulfur or calcium).
Marine oils and specifically the Merc oil blend that many of you defend so strongly achieves the required marine certifications in several ways. An anti-corrosion additive keeps the excess moisture at bay, while the viscosity enhancer and pour depressant make their base oil stable over a broader operating range.
Sounds like we have it all covered, but there are a few negative qualities to these additives. The heavy metals need to be use in precise quantities and need to stay in suspension in order to be effective. Too little in the mix due to poor quality control, or additive fall-out in the oil pan, and the skirts are going to get scratched. Too much, and this stuff ends up in the combustion chamber as tiny little blobs of glitter that glow at superheated temperatures causing pre-ignition like you would not believe.
The pour depressants, viscosity improvers, and moisture dispersants seem harmless enough, but they all have one thing in common. They decrease the carrier oil's base line lubricity. That's not a good thing.
I think the Merc oil is fine and if that is what makes you happy keep using it. But I think we can do better under certain circumstances. Engine builders are notorious for being slow to accept changing lubrication technology. They want oil that they can get in limited quantity in their bottle at a cheap price. It needs to get them through their warranty period, but not necessarily make their engine last forever. It's only when their customers insist on a better mouse trap are they forced to provide one. That's what drove Merc to develop their new full synthetic. A case in point is Honda factory approved 5w-20 premium motor oil. Available at their dealer network, this stuff is actually Mobil Clean 5000. That’s the bottom of the food chain at Mobil. Will it go 5,000 miles in your new Acura and get you to the end of the warranty period. You bet. Can you do better for your new ride? You bet.
So what about Synthetics? Remember the molecule size discussion earlier? Mobil-1 is made from PAO ester base oil manufactured by Mobil Chemical. They take a base fluid and through catalyst technology are able to re-arrange things at the molecular level ending up with a base oil with nothing but the medium sized molecules we are looking for, which is stable over the complete operating temperature range. Straight out of the tank, it can out perform the best conventional oils, without the need for additives. Mobil has developed special additive packages to enhance these formulations even further to the point where these oils can do things never thought possible.
http://www.mertenmarine.com/servlet/the-359/MerCruiser-Full-Synthetic-Engine/Detail
