53 331 Oil Viscosity

[Jim Govoni CLC 20546]

Hello all; I have some questions regarding engine oil: 1.  The tech manual recommends 20 weight oil for the 1953, 331. 2.  I can no longer find Straight 20 weight, is 5W-20 the way to go?
3.  Is synthetic worthwhile if you change your oil only twice a year with less than 1,000 miles driven? 4.  I live in the mid-Atlantic, is a change twice a year good for less than 1,000 miles? Thanks, Jim

[Geoff Newcombe #4719]

A lot would depend on the engine.  Is it freshly overhauled?  50,000 miles?  100,000 miles?  For a fresh or relatively low mileage engine that is not burning any oil, or lets say very little, I would go with 10W-30.  After that it depends on just how worn it is and I would go with 10W-40 or 20W-50.  It probably goes without saying, but todays oils are far superior to anything available back then.

[Geoff Newcombe #4719]

Forgot to add ----- I would definitely not use a 5W-20 or 5W-30, synthetics for a low use car are basically a waste of money, twice a year changes in your case should be fine.

[Jim Govoni]

The engine has 39,000 miles, smokes occasionally on start up. Why the higher viscosity? Wouldnt lower be easier on the engine? Thanks,  Jim

[Geoff Newcombe #4719]

We are talking about multi-viscosity 10W-30, 10W-40, and 20W-50 oils here.  When cold they will flow like the lower number, which is what you want, when hot the additives make them PERFORM like the higher number.  You are not being hard on your engine by using the 40 or 50, you are making up for the larger clearances due to wear and hopefully, maybe, using less oil.  A little smoke on start -up sounds like valve guide seals to me.

Newer engines using 5W-30 are built to use it for better fuel economy, the lower viscosity does create less drag and requires an infinitesimally (there is such a word isnt there?) smaller amount of horsepower ---- possibly giving slightly better MPG and the automakers are looking for ANY inexpensive way to increase MPG.
Again, personal opinion and choice here, I would NEVER use a 5W-30 in a big ol V-8 like yours (or mine).

Please note ---- this is all personal opinion and/or school of hard knocks on my part.

[Mike Josephic #3877]

Geoff:

I agree with you -- I would use 10W-30 or 10W-40 in these 50s engines.  In fact, the Cadillac literature in 1955 indicates that the then new multi-vis oils, specifically, 10W-30 are recommended for the 331 V-8.

A also agree, that I would never use a 5W-30 or the other oils recommended for the newer cars.    Mike

[Jim Govoni]

Thanks for all your help. I understand the deal now. Boy, those oil manufacturers web sites can sure be confusing. Do either of you have an opinion about motor flushes? She sat at the resto shop for 16 months being started off and on and never warming up?
Thanks, Jim

[Geoff Newcombe #4719]

I would get it warmed up and then change the oil & filter while still warm.  Then run it some to get that fresh oil well circulated, drive it around some would be best if that is possible.   I am not one for motor flushes as a rule, they often create more problems than they might solve, and in my opinion it is not called for in this case anyway.