Classic/Antique Car Repair: modern oil/older engine, sae 20, sae 40

Question
Hi Dick:
I have a 1938 Chevrolet with the 216 engine. The shop manual recommends SAE 20. As you noted in an earlier question, straight weight oil is becoming harder to find, especially 20 wt. (Valvoline does still list it on their website.)
I can find SAE 10, SAE 30, and SAE 40 fairly easily. Which of these straight weight oils could I use in the 216? Secondarily, if I can't find straight weight oil can I use a multi-weight?
And finally, do I need a lead additive in today's gasolines? The engine is stock.

Thanks for your help. I really enjoy reading your responses to people's questions and slowly expanding my mechanical knowledge.

Bill  

Answer
Straight 20W oil would be a bit thin if the engine has any wear on it at all.  That recommendation really was intended for the car when it was new.  If the engine is in really good shape (rebuilt within the last 10000 miles), I'd use SAE30W in it for most conditions, and in really hot weather, I'd go to SAE40W.  If the engine is a bit worn, use SAE40W all the time.  

If you are unable to find the 30 or 40 weight oils, I suppose it is OK to use a 20W50 multi-weight oil, but I personally don't feel those are good enough for the old engines, and I don't use them.

As for lead additives for the gas, you definitly don't need it unless you live in the Sahara desert, pull a 10,000 pound house trailer, and drive 80 MPH for hours on end!  In other words, for normal collector car use, there is no reason to add anything to the gas.  All the horror stories that were put out by the trade about valve recession were much overblown.  It is true the when you have the head redone, you should consider putting an extra $500 into the job to have hardened valve seats installed, but I certainly wouldn't spend the money until you need a valve job for other reasons.

I've seen once case of valve recession in my total experience, and that was on a station wagon with a big Chrysler 413 (a 1964) that was used to pull a heavy boat across the Mojave desert every summer weekend from LA to the Colorado river and back -at 80=85 MPH with the dual AC unit going full blast, by a retired Police chief (who had no worries about speeding tickets).  The engine had over 150,000 miles on it, mostly from that service, and it did show signifigant valve recession when I pulled it apart.  In that case, I did convert it to hardened valve seats - and as far as I know, it is still going strong ( the owner moved to Canada in 1997)

I drove my 1951 Chevy Pickup from 1975 to 1994 on unleaded gas (same engine as yours), and it had no problems with the valves at all.

Dick