Mixing oil

[tch911]

I have a Chimp 400 engine that has had a recent oil change with semi-synth oil, with the weight apparently "as per the manual". The previous owner does not know what weight he used. I am thinking of topping it up with Castrol Racing 10w60, a semi-synth oil. If the oil in there is 10-40 or 10-50, am I moron for topping it up with 10-60? What happens when you mix a little bit of one oil with a lot of another.

I intend to change the oil soon but need a top up for a track day on Friday and don't have time to do the change in the meantime.

Thanks

[that daddy]

this wont cause any problems,jusy remember that the oil companys lubrication package works best on its own,now if you mix with another brand you may dilute the package slightly.if your changing soon then it will be fine.good luck with that track day.me personally i would want to do an oil & filter before the day.the engine will meet much harsher/heat conditions on the track.

[tch911]

It's only a tuition day on an airfield with sporadic bursts of full throttle. It'll probably get a better work out on the way there!