[Chris-Austria]

Originally Posted by AdamIsAdam

Did they say why?

As for 5W-50, why doesn't every oil have a really wide range? I thought I read a reason why they don't years ago but, well, I don't remember breakfast, so.

I understand why new engines are made for lower weights, but why not make everything use 0-xx?

The owners manual of my 66 GTO says that 10w30 or 5w20 is an acceptable alternative to the straight 20w or 10w. 20w50 is even thicker than the factory recommended.

A really wide range in viscocity is only possible with synthetic oils like the modern types. You probably could use 0w40 as well.. I never tried. The Morel lifters (HR) recommend 5w40 for the ones I bought... Butler said I can use 20w50.. I trust them but I think where I live I don't want a thick oil at startup all the time.

Maybe a synthetic oil will leak more if you run stock gaskets or if they haven't been replaced for a long time.. oil pressure with the 5w50 is also about 5psi more when really hot compared to the 15w40 I used for break-in.