Oil...again

Oil weight varies for weather reasons; when it's cold, it needs to be thinner, hot should be thicker. All oil is interchangeable, a
s they overlap each other significantly. I live in SOCal, use 20/50 for nearly everything.

And don't forget that the first number, with the "W", is the weight when the engine is at ambient air temp. The second number is what it gets to when the engine is at full operating temp. Ambient temp has an effect on exactly where that is. So at very low ambient temps the oil needs to start out thinner and the engine will not really reach as high an operating temp as it would at higher ambient air temps. At high ambient air temps the oil should be a little thicker but not as thick as when the engine does get up to higher operating temps. The layman's explanation of variable viscosity oils.

Per the chart above, which is common in the service manual for almost any bike or even cars, any weight oil from 30 to 50 will work for full operating temp of the engine at higher ambient air temps.
Only the low weight part of the number varies a lot depending how cold it can get to when you try to start the engine. I ride in temps from around -15 F up to just over +100 F so a 10W-30 will work for me. But I usually would go with the 5W-40 of Rotella T6. I know that recently Shell changed the formulation of T6. But when I last looked the back label did still say that it at least meets the criteria for JASO MA/MA2 which is most important for bike with a wet clutch like the CTX1300. Since Walmart is where I usually got the best price on it I kept looking for them to get more in stock but the shelf remained empty for the entire year so far so I went with the SuperTech 4 Stroke full synthetic motorcycle specific oil, the bottle with the silhouette of the sport bike on the front. It's a 10W-40 which will still work for all the temps I ride in.

Oil threads can be very opinionated about what brand. Many brands will work fine so I try to never say one brand is best since I don't believe any one brand IS best in all situations. You can use what you want as far as brand or viscosity within the limits of certain factors. 10W-30, 10W-40, 5W-40, doesn't matter. They will ALL be the right oil for you if you don't exceed the low temps ratings as given in that graphic above. You can use Full Synthetic, Synthetic Blend, or full dino oil. Most Synthetic oil is made using dino oil anyway but modified to not break down as fast.

@LaGrasta 's chart is the same as what is shown in the service manual for the CTX1300 so you can use any that is shown there. These are guidelines, not hard and factual limits. So as long as the low temp is paid attention to you'll have the right oil. All the viscosity ratings listed work at the high temp limits and it is unlikely you'll be riding so far over 100 F that you have to worry about anything different. And don't be too concerned if the first and last numbers of the viscosity don't exactly match the pairs or sets of viscosity in that chart as long as each number doesn't exceed those shown. Variable viscosity oils will act like the first number before you start the engine so it needs to be lower to more easily flow to and coat moving parts. Then as the engine warms up the oil viscosity changes toward the second number until full operating temp is reached and the oil will then be at the viscosity of the second number.

That said there are limiting factors that can definitely damage the engine, and more correctly the clutch. That being if the oil is designated as Resource Conserving or Energy Conserving. Those types of oils have special anti-friction additives or modifiers that will damage the clutch plates in a bike that shares the engine oil with the clutch and cause the clutch plates to slip. That is called a wet clutch and the CTX1300 has a wet clutch. There are additives in almost all oils that you may use but some have special modifiers that you want to stay away from for wet clutch motorcycle applications. That designation of Resource Conserving or Energy Conserving is shown in the API Service circle in the outer bottom circle. If that outer bottom circle is blank then that oil should be good to use. An even more important factor is if an oil is rated to meet the certification for JASO MA or JASO MA2. That designation indicates that the oil is formulated to work in a bike with a wet clutch. There are some that are rated as JASO MB which is NOT good to use with a wet clutch but is formulated for bikes with a dry clutch. These factors are really the ONLY factors you need to be concerned about. Use the oil you want within those limits and the engine will last a long time as far as the oil is concerned. The JASO designation is a spec developed in Japan for motorcycles made or designed there and is used in motorcycles from many other countries as well. Most, but unfortunately not all, shops know this about wet clutch motorcycles. There are some riders I know of who have used this wrong kind of oil for their wet clutch engines and have not noticed much, if any, issue. Those are the exceptions and they may yet have a problem in less time than they should. Most who have used this wrong kind of oil end up with an issue with slipping clutches, while in gear, relatively soon after an oil change using those oils. Soon as in only several hundred miles or less.

Here is a graphic that shows what I am talking about with the API Service circle which is usually on the back label of many bottles of oil. Don't pay any attention to the viscosity shown here but only about that bottom outer ring.

bob said:

Keep in mind that just because it says for motorcycles there are many motorcycles that do not have a wet clutch. Make sure any oil you use in the CTX IS made for a wet clutch. JASO MA/MA2 is specifically made for wet clutches.

Click to expand...

I went to my local Honda Motorcycle Stealer to ask about the Honda HP4S Full synthetic. This oil is approved for use in all 2006 or newer motorcycles, ATVs, Scooters and PWC with wet clutch. So I'm good for my next oil change as early as tonight.

HP4S is fine AS LONG AS THE BOTTLE SHOWS THE DESIGNATION "MA" OR "MA2" ON THE BACK. From what I was just reading there may be a T 903 spec oil that is MB which would be bad for the clutch. I THINK the HP4S is also MA so that should be good.

In 1998 the T 903 standard was established and included both MA and MB JASO specifications. In 2006 the JASO MA rating was split into MA1 and MA2. MA1 is sometimes simply referred to as MA.