Oil grade?

If my manual says put in an oil with a viscosity rating of 15W-50, and I put in an oil with a rating of 10W-50 (in both cases fully synth), will that:

a) do no harm whatsoever;

b) not be the best, but not the end of the world either;

c) result in a loud and expensive BANG?


It helps to think about what the numbers mean. 15W-50 oil means an oil that can be pumped as easy as a 15 grade oil when cold, but has the protective properties of a 50 grade oil when hot.

A 10W-50 oil has the same (or similar) properties when hot, but will be less viscious when cold. That could effect how well the pump lifts the oil to the cams, although could mean the oil is pumped easier, however, more seriously, it will mean that when cold, when most cam wear occures, the oil will be thinner and therefore less protective to your engine.

I doubt this would make much difference in a smaller less highly engineered engine, say in a CG125, but in a sports bike, it is probably not a good idea, especially if you do a low of short journeys or cold mornign starts.

Thanks mate.

It seems a very complicated business these days: in addition to the viscosity grade, it seems I have to look out for the “API” rating too. my manual specifies SH or higher.

It wont go bang…but you MUST check the oil more frequently as you will find that it will burn/use more than normal. I used 10/40 in my old RSV and that thing just drank it all…so back to the reco. grade 15/50

absolutely echo what they guys say here - it’s not the end of the world but I’d be changing it a lot more frequently than I would with the ‘proper’ oil.

Must admit I never skimp on oil - always get the best I can lay my hands on.


I’ve ran my old Bandit 12 and my current Z1000 on diesel engine oil 'cos it’s what I get free from work!

In 4 years I’ve stuck to the normal oil change intervals and neither bike has missed a beat or used a significant amount of oil.

Must admit I never skimp on oil - always get the best I can lay my hands on.

Matt, is that 1st or 2nd wash you are talking about

I would never go against what a motorbike company says for grade of oil to use as they are the people who have spents millions bringing the motor to the bike. As for an oil change I’d do this depending on what you do with the bike. If you track it all the time then change it more often than if you just slow ride to and from work.

I had an oil change on the RSV after my Spain trip (3500 miles) as we were going at a good pace all the time and on the way back to Calais we spent a number of hours sitting over a ton. The bike may not have needed an oil change but it made me feel better for it to have one. Been told about people doing over 10K miles between changes and the oil still looking very clear.

IMO (not fact so keep the knives at home ) If you get mobile 1 for your bike over Tesco 1 it will be better for your bike. Cost is more but when your out on a ride to you cover your body with PVC or leather? Both cover your body but one does a better job when needed