Can oil be mixed?

My bike needs oil and I don't know which one to put in it (well I don't know what is already in it).

Manual says 10W 40. Should I top it up with this and if it is a different viscosity to what is in it will it be ok?

Incidently when I done a search I couldn't find a single post on oil!

I don't see as you have much choice. I'd have that that if you follow the manual you should be fine. That's what it should have in it already and in the absence of any history about your bike I can't see why it wouldn't have that already in it.

to be totally honest if you were in an emergency you would put anything in, as long as it has oil it has lubrication, fair enough it wouldnt run as well on something else but if needs must, in the manuel (be it owners or haynes) it should also tell you what oil they have in them or you could always go to who serviced it last and see if they know what they put in it.

It'll be fine, they're all miscible hydrocarbons, whatever the manufacturers say about their magic formulas. You won't be certain what you have till you do a new change. If you don't ask, most garages don't tell you what they put in anyway!

Cheers guys. Had a good mechanic do it's last service so it must be the right oil in there. Topped it up with semi-synthetic 10W-40. It's looking a bit dirty now so will probably do a full oil and filter change soon anyway. Is semi-synthetic a good compromise or should I go fuly synthetic when I do a change? It's an '03 SV650S with 6K on the clock.

[fizzwheel]

Semi will be fine. Its not a high performance motor, so there's no need IMHO to run it on full synth.

[Rich]

I mixed mine and havent had any troubles, as long as you put the same spec oil in it, as the manufacturer recommends it should be fine im told!!!!

Originally Posted by teriyakimonkey

It's looking a bit dirty now so will probably do a full oil and filter change soon anyway.

That's quite normal. If you do an oil change and drain all the old out, fill the new then start the bike up you'll probably see it go mucky before your eyes. Don't worry about it.

I put 5w40 in my bike last time. Lovely stuff that is. Takes time to warm the engine properly, but once it's warm, it runs very smoothly. More of a track oil than a road oil (since track bikes run at higher RPM & load on average).

I say this in every oil thread, but put anything of any viscosity in that you like, but never put car oil (eg, magnatec) in your bike. Your clutch won't like it!

I get a bit confused by oil grades, even though I've learned about them and read the explanation. Having said that...
It's my understanding that you need to be careful putting a lower viscosity oil in a machine than is specified. The seals might not work properly and apparently once a seal is breached by an oil (a bad thing) then there's bugger all you can do to reverse the situation without stripping down and cleaning.