Topping off GC 0W-30 with other oils?

[Deer_Slayer]

I went today to Autozone and took advantage of the great deal they are running on 5 qts of Castrol Syntec and a K&N filter for $25. I got some of that German Castrol (0W-30) that everybody was praising so much to give it a try. but the trouble is my truck holds almost 6 qts of oil, and I hate to pay the regular price $7 for just one more quart to top it off. I have some Castrol GTX in 5W-20 and also some PP in 5W-20. Do you think it would be ok to top off the engine with less than 1 qt of one these two 5W-20 oils? Would it affect the performance or effectiveness of the GC 0W-30?

 

[SuperDave456]

If you have another full Synthetic, like PP, I think that would be ok.
I wouldent mix it with a regular Dino oil to top of a full synthetic if you are looking for extending a interval.

 

[Deer_Slayer]

I forgot to mention that I also have some Valvoline Synpower 5W-30.

 

[Audi Junkie]

I wouldn't, not with GC.