bought a 70 lemans with the 350 guy I got it from gave me receipt for oil change his mech said only run 20w50 , I was thinking 10w40 or should I stay with the 20w50? Had a 69 firebird as a kid with cam ,intake like most kids a ran 10w30 my cousin had a GTO he dragged and ran straight 30w, what do you think?

I am a fan of running 10w30 or 10w40 in my 455. These engines were designed with that oil when they were new.  Now if this engine was rebuilt by a reputable engine builder recently and he changed the engine tolerances that would allow you to take advantage of a thinner 5w or 0w oils, I would stick with what we know works.

By today’s standards, Pontiac V8 specs are much looser than a modern LS/LT engine. Therefore a thicker oil is needed to prevent metal to metal contact within the engine.

hi Hd bob 

i am with frosty ! my 389 runs on 10w30 

has anyone told you we love pictures around here ? i have a 68 lemans, would be nice to see your new baby  

I was told to run straight 30 weight in my 428 while breaking in then run 10W30 as Frosty said. Also, in case nobody has mentioned it yet, we love pictures around here! 

Pic's??? Where's the pic's???

I'll add pics when I figure out how lol

Talk to Ringo bro, he's like the dude behind the curtain. 

2 hours ago, hdbob5454 said:

I'll add pics when I figure out how lol

Here’s some instructions at the link below. If you have questions, please feel free to message me:

 

See, he is the dude behind the curtain!

3 minutes ago, Wrongway said:

See, he is the dude behind the curtain!

Unless some one built the engine extremely tight, which would take some rework on the crank or oversized mains stay with the 20w50. Why? Clearance specs on those mains run between .0025 to .004. A 20w50 oil is only a 50 weight on the high heat end of the engine oil temp. And a 20 weight @ cold startup. So under normal conditions, I.E. moderate heat you have a 30w oil any way. But under worse case scenarios, high heat you have additional protection. The best way to really tell is to have a mechanical oil pressure gage. Given know engine temp + bearing clearance you should have x for pressure. To little pressure you'll scuff a bearing to much & you'll erode a bearing. My two cents.

Edited April 22, 20251 yr by Last Indian