Originally Posted by Jeep2Xfire
generally, thinner oil is used because clearances are a lot smaller. Thicker oil will run off where thinner oil will lif an separate forming a "skin". Good example would be the clearances between rod bearings and the crank. The journals for the cams as well. Once you have metal on metal spinning @ 1000's of rpms, the damage is done...
Thanks for the info it clears things up for me! In Australia we have a racing series where the cars all have the American built 5.4ltr V8 BOSS engines and this is the oil all the cars use, I thought if it holds up in there racing series it should be fine for the Crossfire, I guess I better stick to 0W-40!!