how to determine engine oil grade for modded engine

[shaggy911]

i have 302 with total seal rings and some pistons - by a previous owner.
Currently it has 20w50. i dont know if this is needed or if it will work in the winter time well.

How do i find out what grade to put in it, without screwing up the engine internals? I dont see any need to put 20w50.

BTW what is factory fill grade?

thanks

 

[hollywoodstang]

10W30 is the factory grade. 20W50 is too thick for winter no? I know some people use 20W50 but i just use 10W30, I don't use those expensive oil either, I just use Motorcraft. Good stuff

 

[Cobra1741]

i run 20w50 in my car, but i live in texas where its warmer climate. if you are up north i would say no but the winter doesn't get too cold here so it thins up relatively quick.

 

[shaggy911]

if temps here go down till 10F what oil would you suggest for winter?
And for comparison what does the factory suggest?

I was thinking of using 10w30
My 2004 V6 stang required 5w-30 (or 5w-20 maybe?). But that may be directly related to engine specs which is ofcourse different.

 

[wytstang]

Winter 5w30 all other 10w30, I would use a full synthetic year round if I could (leaky rear main seal=waste). All though next year I do plan on running a full synthetic during the winter months, it has a better cold flow rate then dino. 20w50 is just to thick for engines with close/tight clearances, you don't have a big block from the 60's/70's.