What is everyone's preferred oil weight year round on the Olds small block on the street? I prefer 10w30. I have seen some use 5w30, as well as 20w50. I do use Driven 15w50 in my Pontiac 455, but that one I run a bit hard and usually only drive it in warm weather.

 

I have 20W50 in my 71 98.

 

10W30 on Eastern shoreline of North Carolina.

 

10W30 all year round.

My ride was a partial daily driver and is down to basically weekends only. 4 season weather.

 

Unless you have a high-performance build with large tolerances (or a worn out engine), there's no need for anything other
than 10W-30, maybe 10W-40 if the car sees a lot of hard driving in hot weather.

 

That's exactly what the CSM recommends.

Their chart shows 10W-30 or 10W-40 for temperatures above zero F.

For colder conditions, use 5W-30 up to 20 F.

 

10w-30 in my 350.

Pat

 

I have been running 10W30 VR1 conventional. I ran 10W40 SG Motorcycle oil last time after a flooding issue, no VR1 locally in 10W30. Slightly higher hot oil pressure than 10W30. I am swapping in VR1 10W30 synthetic for the new hydraulic roller cam and Edelbrock heads swap. That will leave one case of 6 VR1 10W30 synthetic. I plan to mix one quart with 5L of Valvoline Restore and Protect 5W30 for the next 6 oil changes. It depends on temperature, clearances and oil pump for what grade to run. I was often hitting 100 psi on the gauge cold with one quart 20W50 and 5 quarts 10W30 VR1. I went to straight 10W30, not quite so high cold and still over 20 psi at 750 rpm hot idle in gear. I have a HV oil pump, purple spring with .0022-.0025" rods and .0025-.0028" mains clearances.

 

10W30 in almost everything here. 15W40 in some big boat engines but thats it. Do remember ever using 20W50

 

Castrol 10-30 in the daily, 07 5.3 GMC and 10-30 VR1 in the W-30.

 

5 or 10w30 in Olds & Chevy grocery getters. In my 434 with “clearances you can throw a cat through” I switched to 10w40 for the fuzzy feeling of keeping idle oil pressure above 20psi in hot weather, as opposed to 18psi with 5w30.

Brand? Pretty much whatever decent quality, “full synthetic” oil is on sale at that time. Over the last 40 years I have used a lot of Mobil 1 in all the family’s variety of vehicles, other than diesel pickup.
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Valvoline 10W30 VR1 in anything I own with a flat tappet cam. The Toyota gets 5W20 Mobil 1 and the best filter I can buy.

 

Weight, especially on a rebuilt engine, depends entirely on clearances. Use whatever weight gives you good (10psi to 20psi is my goal) hot idle pressure without wasting energy. 80 psi hot idle isn't doing anything useful for anyone.
I start with 10w40 and move up or down depending on how the engine reacts. Thinner cold weight is almost always better so things get lubed at startup. But a huge weight spread, like 0w50, requires some very complex manipulation to the oil base so if you're trying to run conventional (which is a must for seating rings) then you're limited to a 30 number split or so.

If pressure is super high then that means the engine is struggling to get oil to move through the system and that's not necessarily great.

OEMs, especially today, are able to control clearances really well so they can make blanket oil spec requirements. Well, unless you're GM or ... shoot, I forget the other engine recently... where they went too tight and engines are failing. It's an interesting mess - OEMs are moving to thinner oils because you get 0.01% better efficiency (and every iota counts at the fleet level), but need tighter clearances to keep control of the oil so it doesn't just pour out at the first bearing, so you chase your tail down the spiral and ... boom. spun bearings.