a weried question about 2t oil

hi this is a strange one but i have been running my sr 125 on castarol fully syinthetic raceing 2t for the last year but i want to change to motoul 710 fully syinthetic as i hear its good but my mate just did the change and he didnt drain the tank of castarol he just simply mixed the 2 together so for a while theres was both brands in one tank it worked fine the motoul started feeding through but litrally after a day of the motoul comming through the engine just seized (he wasent reving the tits of it or anything like that he was simpaly on his ay to work before the seize engine was compleatly helthy) and he recons it because he changed the brand of 2t oil is there some truth to this or is it aload of bulls**t ???

please reply asap as i am very curious

 

the new oil he put in could have been pre-mix and may have been too thick for the pump to pump through. Normally its not a problem mixing like for like oils..synth with synth etc

If your bikes running good as is, then why bother changing unless your getting the other oil mega cheap?

BTW, IF you do need to swap disimilar oils, just run the oil tank WAY down and then top up with the new stuff...just dont let it run dry in doing so

 

thanks very much your advice is very apprecited