Pennzoil does not give any product specifications for their yellow bottle oil, or at least not on their web site a few minutes ago. Castrol gives very little, nothing really useful.
However, from VOA and UOA, the GTX has better specks, additative package looks better "TO ME," is a more robust oil at least on paper. However, Pennzoil may, or may not, have a beter base but if they do it doesn't jump out on UOA over GTX. If you want a conventional 30 weight oil that is a little on the light side, cSt wise, and don't push your OCI, I think you would be happy with either.
Given the choice between just those two, I would go with Castrol but I do not think Castrol is the oil it used to be.
I did use Castrol from 196? until 1990. I used it in a variety of vehicles. When Mobil 1 became available to me in 1990, I switched to it and have used in ever since.
However, from VOA and UOA, the GTX has better specks, additative package looks better "TO ME," is a more robust oil at least on paper. However, Pennzoil may, or may not, have a beter base but if they do it doesn't jump out on UOA over GTX. If you want a conventional 30 weight oil that is a little on the light side, cSt wise, and don't push your OCI, I think you would be happy with either.
Given the choice between just those two, I would go with Castrol but I do not think Castrol is the oil it used to be.
I did use Castrol from 196? until 1990. I used it in a variety of vehicles. When Mobil 1 became available to me in 1990, I switched to it and have used in ever since.