YOUR ENGINES BEST FRIEND- MOTOR OIL 
The selection of motor oil that is best for your engine seems to be a subject that is like the never ending story, and  it seems to be constantly under discussion among RV folks and just about anyone else who owns an internal combustion engine. The idea of which motor oil to use, what grade or weight is best, and decidedly which brand is better has been the subject of  spirited conversations around RV campfires for quite a time now. Some  ideas are fueled by stories passed on from friends, others generated on beliefs expressed by the service mechanic who cares for you vehicle, and some even from industry advertising   that stretches oil claims to the limit, often backed up by which NASCAR driver uses which brand.          
While all of this information makes for a great campfire bull session, it is vitally important that you consider facts, and they are given to you in your vehicle manual telling you what weight and type of oil to use under certain operating conditions. These operating facts have been arrived at by extensive testing to determine what is best for your engine. However the manual leaves it to you  to make a decision as to what conditions your engine is working under. I am of the opinion that if your driving a Blue Bird, your engine is performing just about full out a good share of the time, so I consider the engine always working under adverse conditions and perform oil changes accordingly !
 Next you need to know that when it all shakes out engine oil has three basic jobs. First it must protect against wear, second it has a big job of transferring heat away from engine parts and third it must protect against  harmful deposits often generated by the engine during the combustion process. 
 
WEAR
Basically your oil protects against wear by keeping a microscopic film of oil between all moving engine parts. To do this the engine oil must maintain the ultimate lubricating viscosity or thickness. Too thick it will not flow to all places needing lubrication. To thin it will not provide the film required to sufficiently protect. Then to complicate things, different engines use differing oil weights. Sometimes the engine oil manufacturer will add a anti wear additive to assist this function. Additives can also neutralize combustion byproducts with detergent additives, thus doing away with corrosion.  Should your owners manual recommend a certain brand of oil, it will likely be because of the additives in that oil and not because they are trying to sell any brand of oil.

HEAT
Heat transfer or removal is one of the bigger jobs motor oil accomplishes for you. Pistons are constantly exposed to high temperatures of combustion, and they need far more cooling than that provided by the engine cooling system. Much of the cooling comes from motor oil spraying the underside of the pistons and carrying considerable heat off to the engine oil pan where it dissipates to the air. Without this extra oil cooling, the effect of combustion heat on the pistons would cause catastrophic failure of pistons and valves. A good oil has antioxidants that protects the oil from extreme heat while performing this cooling function and extending oil life. In the interest of efficient heat transfer, it is usually a good idea to keep your engine's oil sump pan free from layers of dirt and caked on oil sludge.

ENGINE DEPOSITS
When combustion takes place in the engine, engine deposits often result as by product and pollute oil and contaminate it as it carries away the heat. As oil gets more and more contaminated it tends to thicken and deter good lubrication. To help neutralize this, oils will have a blend of dispersants and detergents to fight the problem. It is very important to select oils with adequate and long life detergent additives so that they carry the particles into the oil filters to be trapped there and keep your oil cleaner, longer.

MULTI VISCOSITY OILS 
Perhaps one of the greatest inventions concerning motor oils was the blending of multi Viscosity oils . Oils with a label of 10w30 or 20w 50  are oils that can serve you all year around and depending on their selection, serve well..  To blend multi viscosity oils the manufacturer must first choose a light base oil (5W,10W,20W) then they add polymers to them to prevent the oil from thinning as it becomes warmer. For example at cold temps a 10W 30 oil will flow as their lower number indicates because when cold the polymers are wound up in a tighter chemical chain. As the oil warms up their polymers literally unwind into longer chemical chains that prevents the oil from thinning equal to more than a 30W normally would. The result is that at 100 degrees C the oil will equal what the higher number indicates. Choice of multi grade oils for an engine differs from engine to engine. That is why  I repeat that following the engine manufacturers recommendations is important. For example you do not use multi viscosity oils in either the 6V92 or the 8V92. They call for straight 40 weight oil, and I favor Shell Rotella because of its additives which copliment a two cycle engine. 
  
OIL CHANGE INTERVALS  
Perhaps the next most popular topic is how often to change oil. 
Not to worry, just remember that the key goal in engine oil change is to keep engine oil free of pollutants, with additive fully functioning, and doing the job it is supposed to.  I deviate from manufacturers recommendations and  with a gasoline engine I change oil and filter every 3000 miles. Admittedly this may be too often, but it is my insurance! A diesel every 8000 miles along with fuel and oil filters. This  I do to be certain oil is clean. But the book says that if you follow manufacturers recommendations to the letter you should have no problems and perhaps that is good enough. I just want to be sure!

SYNTHETIC OILS
The more expensive Synthetic oils have excellent lubrication qualities and have the tendency to keep engine bearings very happy for longer oil change intervals.  They have superior high temperature oxidation resistance, a higher film strength, and many other better qualities than standard motor oils, but at a  higher cost. It must be left up to you to determine if the higher cost is justified for your application. Usually synthetics can be operated  three times as long as petroleum oils without concern. 

OIL ADDITIVES
Oil companies go to a great deal of trouble to blend and test motor oils so that they will perform as specified in you engine. Very often the careful blending and balancing of additive can be easily upset by some well minded individual adding what  they think to be a great oil additive. The result might be that the oil will no longer performs to the intended specification!
Simply put, do not use additive in your motor oil!  .

OIL TESTING
Some large truck fleet owners use the oil sample test procedures to determine when oil needs to  be changed. This entails visiting your local auto parts store and obtaining an oil sampling kit. You then draw off a sample of motor oil and send it to a laboratory for analysis. The report you receive will tell you of the carbon and pollutant content of the oil sample, and also what kind of metal shavings might be present in the oil. Knowing which bearings in you engine is made of, the presence of a certain metal can tell you the extent of bearing wear in your engine. Note that  bearing wear has to be determined over the course of several  samples and can not be adequately determined from a single sample.
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Remember, oil and filter changes are your engines best insurance policy, so do it regularly, and in accordance with your manual!

Harvey Lawrence
Rockport, TX