In Reply to: The Castrol Syntec 5/50 is not a blend of any sort posted by more on September 13, 2000 at 10:20:44:
"Castol Syntec is HYdrocracked and Hydroimerised. Yes is it is a good base stock but is still API Group II. It is very pure but not as pure as say a GroupIII or IV base oil. On one of your posts on noria you questioned the european spec Castol 10w-60.It is a PAO based oil,castrol does not use hydrocracked base in there oils that they market as synthetic in europe."
From what I undersand the BMW brand oil that is produced by Castrol Europe for BMW is good stuff. The stuff we buy off our shelves here in the US though is NOT the same. There was big lawsuit over this a year ago but surprisingly the judged rulled that Castrol could keep the name synthetic on the label despite the fact that it was a petroluem base. The class II hydrocracked petroleum base is not as good as the PAO base like Amsoil amd Mobil-1.
It is 100% synthetic...just like Amsoil and Mobile 1. However, given bob's comments, i think i'll switch back to Mobile 1 extreme 0/30 (what I used before) before my next track event.
You have obviously done some homework. I use Amsoil 20W50 in my track car (in Florida) for a couple of reasons. 1) I just can't shake the thicker is better old school thinking for the real extreme temps we get at Sebring (I have seen 250F on my gauge). I know this is kind of dumb but I have yet to try the 0W30 on the dyno to prove to myself that I am giving up any power. 2) I like the extra zinc and phosphorous the 20W50 has.
Regarding the other gentleman's comments about 5W40 am 10W50. There is more to be lost than gained with these oils. First, I believe these are Syntec blends which, in the US, aren't even in true PAO synthetics. They are better than most petros but they are in a completely different clasification of base oil than Amsoil and Mobil. Second, any oil that has a viscosity spread of more than 30 points is using a viscosity modifier to get the extra spread. The VM breaks down faster than the base oil (particularly in track conitions) and eventually causes the oil to behave like a straight 25 or 30 wt oil. The cold start beneifit you originally bought the oil for is essentially gone by the time your drain interval is reached. In this scenario the 0W30 is better for your car per Bob's argument.
The point is, if you are using your car on the track, use the best like Bob does.