Late last year, The Honda Motor Company changed its commercial engine oils they have for sale in their motorcycle outlets in Thailand so that now you can only get the 10-30 viscosity range. Before this, you could buy a single grade oil 40W that offered sufficient protection and, if I remember correctly, a 15-50 multi-grade oil.
I am seriously concerned about this change, and the effect this thinner oil may possibly have on engines during long distance driving. The first question must be, why did the company change its engine oil specifications in this way? Was it because they wanted the engines to last less so they could sell more motorcycles in the long run? I asked a very knowledgeable motorcycle mechanic here in Bangkok, and he gave me the following answer: Honda did this because they felt the other oils did not provide enough safe lubrication to the upper part of the engine, i.e. to the cylinder heads and valves. I don't really believe this.
Volumes could be said on the topic of engine oils for cars, trucks and motorcycles. The issue is complex and simple at the same time, and a lot of misconceptions are all around. Believe me, it is very rare to find a person who understands these issues in any depth in repair shops, garages and especially in gas stations that do oil changes. Most of the people involved in this line of work do not have any concept of viscosity, additives, mineral oil and synthetic oils. As this is a topic that I am profoundly interested in and could write about at length, I will have to restrict myself in order to prevent this from becoming too involved or too boring.
I believe in the following principles when it comes to engine oils for all kinds of vehicles:
"The most important single maintenance activity is to change the oil and filter on the engine-maker's schedule."
"Engine oil should be changed at 100 hour intervals."
"Oil collects moisture from condensation in the sump and is the repository for the liquid by-products of combustion. These by-products include several acid families that, even in dilute form, attack bearings and friction surfaces. No commercially practical filter can take out these contaminants. In addition oil, in a sense, wears out. The petroleum base does not change, but the additives become exhausted and no longer suppress foam, retard rust, end keep particles suspended. Heavy sludge in the filter is a sure indication that the change interval should be shortened, because the detergents in the oil have been exhausted."
"Most manufacturers are quite specific about the type and brand to be used. Multigrade oils (e.g. 10W-30) are not recommended for some engines, because it is believed that they do not offer the protection of a single weight types."
(Quotations from Paul Dempsey: Troubleshooting Diesel Engines, 3rd Edition, TAB Books, Division of McGraw-Hill, Inc., 1995.) (You should not let it trouble you that this book is about diesel engines as what I quote is true in general of all engine types used in all kinds of motor vehicles).
The bottom line is that I am not convinced that multigrade oils such as 15W-40 or 15W-50 offer the same level of protection as a single grade 40W does. Especially in Thailand. If you look at the tables recommending suitable oil thickness and viscosity to outside air temperatures, you will see that for the climate and temperatures prevalent in Thailand, 40W is the recommended engine oil thickness, given the average temperature in the country.
You may say, yes but the multigrade oil will act as 40W when that is needed. I say no, I am not sure and I am not convinced of that. First, the multigrade oil is made multigrade by additives and thickeners. It will never protect your engine as well as a single grade 40W oil in hot temperatures, especially not when it has been used let's say for 50 hours or more.
Is fully synthetic oil better than mineral oil? I am not convinced of that either. Research has shown that the long molecule chains in synthetic oils start to break down sooner than the shorter molecules in original mineral oil, and once this process is under way, the synthetic oil is much worse than mineral oil and does not offer the same degree of protection.
Let's look at some situations. With an outside temperature of 29-33 degrees Celsius, such as is common in Thailand, why would you need an engine oil that goes from 5W-40? All you need is the W40. Anything thinner than this is just going to make your engine wear down all that sooner. Offering oils such as 0W-40 for sale is just ridiculous in a sub-tropical country. Yes, if you live in Ontario, you will need a thinner oil for start-ups in close to zero or sub-zero temperatures, but how often do you have that kind of situation in Thailand? The answer is: Never.
In my opinion, real knowledge about engine oils is not common, and especially rare among engine oil sellers and distributors in Thailand. Most of them are very ignorant on this topic. About all that many of them "know" is that one kind of engine oil is more expensive than another, and so therefore it must be "better". That is pure bullshit, of course.