Oil Viscosity
 

What oil viscosity should I use in a 1973 280 carb 6-cyl car. Mechanic put in 15W-40 due to its age and it blowing some smoke at start-up. Where can I buy 15W-40 (could not find at Auto-Zone)

use Castrol 20W-50.

I use Castrol 20-50 all the time in the warm months, 10-40 in the winter...works fine but it won't correct valve stem leakage which it sounds like you have. It's really no big deal and the way to tell is this....if the engine is stone cold and the exhaust blows white smoke out then it's coolant and that's not good. If the exhaust puffs alittle dark blue or even greyish smoke out upon cold start that is not so bad but expected. If the engine smokes upon a quick restart when warmed up, white is really bad and blue is not so bad but both represent an issue. As long as the engine is not leaking any fluids visably and burning maybe a quart of oil every 1000 miles I wouldn't worry about. If the coolant is going away that's a problem. Valve stem seals are not a big deal but are typically done as part of a valve job, but as long as you keep the fluid levels up you could drive the damn thing virtually forever....good luck

you should just replace the valve stem seals, its really not that hard to do, but it does take some skill.

Autozone sells many brands of 15w40, that is a diesel weight oil. Rotella, Delo, Castrol.....there are several. Its on the separate shelf from the normal oils.

paw is giving you the correct information here.

It is not the weight that you are looking for as correct lubricant for this engine. It just so happens that 15W40 is what is termed Universal Grade and is what the truckers use. It has additives necessary for your engine that are not included in more standard engine oils, Castrol included.

The main additive that your engine needs is the zinc additive that has been dropped from most all oils except Universal Grade and most Racing Oils. The zinc additive is for health of flat and sliding cam followers. All modern engines use roller cam followers eliminating the need for this additive. The oil suppliers quietly deleted this from their additive package in order to put more profit in their pocket, but never bothered to tell anyone.

For your old six, use Chevron Delo 400 (my favorite,) Mobil Delvac or Shell Rotella T(has higher parafin content than the other two.) These are the most commonly available.

As an added bonus, these oils have more detergents that are used for soot dispersal in a diesel. These detergents will help prevent sludging in your older engines.

Delo 400 or Delvac Super would do the best, will clean up the insides and keep the rings sealed.

Thanks for the reply’s. It does blow some smoke on a quick start-up once warm but I find it hard to determine exact color. It's not snow white but it's not real dark either. The oil is down a little when I check it but the coolant is always fine. I just got the car back from the mechanic who had it for a couple months getting it going. It's was in my garage for the past 9 years. The first couple years I tried to turn over the engine but it never started then over time I didn't even do that. I want to run it for a while and then see what I need to do next, possible the valve stem seals.

Link to Mobil oil site. Note Zinc levels

https://www.mobiloil.com/USA-English/MotorOil/Files/Mobil_1_Product_Guide.pdf