10w50 Oil in a 996
 

I remember reading on the forum quite a while ago a recommendation for using 15w50 oil in a 996. (i know i put 10w50 in the title)

I can't find that thread know, but can anyone shed some light on this please?

I going to change mine in a few weeks and i normally use 10w40 in all my bikes so i'm just interested to know why.

cheers
Simon

The 996 tends to burn off the thinner 10W40 oil, the Ducati 2000 Tech poster actually lists Shell Ultra 20W50 for the 996, my preference is for Silkolene 15W50 in my 996, I know others use Motul V300 15W50 and don't seem to suffer the drop in oil level you get with the thinner oil

Viscosity Reduction
 

The main reason for using a higher viscosity 50 weight oil is that the oil looses viscosity because it also lubricates the transmission.

The central dogma of motorcycle oil manufacturers and distributors has always been that motorcycles put different demands on their lubricants than do automobiles. In particular, they point to the facts that motorcycles run at higher temperatures and use the same oil in their transmissions as in their engines. The transmission gears supposedly put extreme pressures on the oil molecules, thus causing the long oil polymers to break down. High temperatures can have the same basic effect, as well as additional effects such as the increase in oxidation products.

When the size of the oil polymers decreases ("cut up by the transmission gears," as at least one manufacturer claims), the oil thins. In other words, its viscosity decreases, as well as its ability to lubricate properly. For example, what started out as a 40-weight oil could effectively become a 30-weight oil, or even a 20-weight, after prolonged use.

The viscosity of synthetic-based oils generally drops more slowly than that of petroleum-based oils in the same engine.

Here's the result of one test.

Castrol GTX, a non-synthetic car oil at 800 miles showed a relative viscosity of 0.722, meaning it had retained 72% of its original viscosity. Or, if you want to look at it the other way, the Castrol had lost 28% of its viscosity after 800 miles of use in the motorcycle.

Just for comparison sake, they also tested the viscosity drop of the same Castrol GTX oil after use in a 1987 Honda Accord automobile. At 3,600 miles of use, the Castrol GTX showed a relative viscosity of 92%.

So a motorcycle is definitely a more severe operating environment than a car so the oil change mileage interval should be shorter than for a car.

In the same test, since Mobil 1 car synthetic oil had retained so much of its viscosity after the 1,500 mile test, it was the only oil allowed to run longer in the motorcycle. After 2,500 miles, the Mobil 1 recorded a relative viscosity of 79%.

One more point. If you buy a motorcycle-specific synthetic oil it's no guarantee that you can extend your change interval. There were two motorcycle oils tested, Spectro 4 (petroleum based) and Honda HP4 (petroleum/synthetic blend). Both the Honda HP4 and Spectro 4 had lost over 30% of their viscosity at 800 miles, and over 35% at 1,500 miles.

So, my choice is to use Mobil 1 15W-50 automobile-specific synthetic oil and change it at 3,000 mile intervals.

Your oil viscosity selection chart in your owners manual tells you to change to a thinner oil if the expected outside temperatures are lower. As you can see from the chart, a single modern motor oil with viscosity enhancers can be used over a wide range of ambient temperatures and still maintain adequate oil pressure. So oil viscosity not a sensitive parameter.

Thanks both for responses :-)

Very interesting on the wear on the oil in a motorcycle engine. I knew that the gearbox created a much harsher environment, but to loose 28% viscosity after 800 miles is a surprise!

So given that the oil looses its viscosity quite alot, do say Honda take that into account when they recommend 10w40 for the Fireblade for example? Or could one play it safe and put in say the 15w50 knowing that it will reduce its lubrication properties?


@skidlids - i think that it was your original post that i remember.

Opieoils.oc.uk have the Silkolene at a good price and only £1 delivery at the moment so i'll get some of that (along with oils for my car and bike).

Cheers
Simon

So, my choice is to use Mobil 1 15W-50 automobile-specific synthetic oil and change it at 3,000 mile intervals.

I'm not saying don't but be careful about putting Passenger car oils in a motorcycle engine unless it is running a dry clutch, the friction modifiers used to improve fuel economy may cause clutch slip issues.

Hi Simon, I buy quite a bit of oil from Opie and get my DSC Discount with them as we are a registered club