I have 4 quarts (truck takes six) of some 5w-30 synthetic oil in the garage made by a company called "Synthetic." Is it alright to just buy two more quarts of Castrol Syntec 5w-30 and put it all in together? Thanks...

 

I would never put generic oil in my truck. My truck is one of my largest investments, why pinch pennies on the most impoertant maintenance item?

Dude, toss that stuff in your lawn mower and buy 6 full quarts of M1 or RP or some other name brand quality synthetic. I run M1 have always run it in all of my vehicles. Makes me feel all warm and fuzzy.

 

By the way, I understand Castrol Syntec is not 100% synthetic.

 

i run royal purple. its a little pricey but well worth it IMO.

 

It would be totally fine, people get a little crazy on the oil.

 

Yea, you can mix different brands. I agree that I don't like generic brands of oil though...my father did some dyno testing a few years back comparing oil brands (kinda like that Castrol commercial, for heat and viscosity break down etc.), and there definitely is a difference from one brand to the other, as far as quality goes. He tested mostly conventional oils, and also Mobil1 synthetic. Mobil1 was the best, and Texaco Havoline was the best of the conventional oils...Castrol was another one that was near the top. Among the bottom brands were Quaker State and Valvoline, if I remember correctly.

 

I wouldn't do it...might be good might be not so good...different additives,etc. Like the others said put 6 qts of Mobil 1 or another well-known full synthetic. You wouldn't want to hurt a friend (engine) would you?