Originally Posted By: Patman
Originally Posted By: OVERK1LL
Compare the MRV of PYB to GTX and you'll see what I mean.
You have to keep in mind that the data sheets Castrol gives out for GTX doesn't give an actual MRV value on it but instead it's telling us the maximum value. That just means that the oil has to be less than that value in order to qualify as a 5w30 for instance. Castrol has never been good about giving out specific data like that, but it doesn't mean the cold cranking performance of GTX is not good.
I'm very impressed with the cold cranking performance of GTX 5w20 in my wife's Civic. Even at -22C the engine never sounded labored on that first morning start, it turned over quite easily.
IMO, when it comes to the choice between YB or GTX, I'd go with whichever one is on sale for a lower price. I believe both are excellent oils and you can't go wrong choosing either one. Up here I never see YB 5w20 on sale, plus it's not sold in the bigger jugs either, so those two reasons are why I'm using GTX 5w20 in the wife's Civic.
I agree that Castrol's data is somewhat vague.....
That being said, I never noticed any laboured cranking with 5w40 either