Hello - I've got a '76 Cutlass Supreme with the 350 and a catalytic converter. I have not been able to figure out the best oil to use. I've read that the best thing is something like AMSOil for the higher mineral content similar to what was sold in the 70's. But then I've heard that the higher mineral content would ruin the catalytic converter. Does anyone have any advice?

 

Well, they used cat converters as early as 1975 and had a much higher zinc content than even the most zinc rich oils now and it didn't kill the cat right away back then and even if it did do it in a little sooner your flat tappet cam will thankyou

 

Chris,
Higher Zinc content, not mineral.
Zinc or dialkyldithiophosphate (ZDDP) is the most commonly used anti-wear additive in motor oils in older flat tappet(lifter) engines such as yours. It had high zinc in it from the factory in 76. Cat converter has no real relevance to oil in this case. Hell take a prybar to that cat and break out the honeycomb wash coated substrate! Let it breathe! No more worries (Kidding...sortev). No sniff test here in Rottenchester/Taxchester/Libchester! The Zinc has been slowly removed from oil as today's engines commonly use roller tappets. The oil companies are able to back off on the zinc and save a nano cent.

Google high zinc oils and select one to your liking...I recommend 10W30 or 10W40. Separate additives such as Amsoil are acceptable to use with today's lo ZDDP oil. Schaeffer is my fav. South Town Beverage owners (Henrietta) are a dealer of this product.

Do you attend Damascus Shrine Cruise night on Friday nights on Bay road in Web? If not I highly recommend it! 3-8pm 4-600 cars(in and out) I'm usually there. Look for the only red 68 442. Im planning on attending this week as its not gona rain for once.

 

Chris,

I am using the Lucas 10W-30 in mine and it has Zinc in it. It seems to be working fine. I purchased the 5qt. Jug thru Amazon.

Thanks,

 

Thank you..

 

Droldsmorland...thanks for the headsup about the Cruise night...I'm definitely going to try and get there..I'll keep an eye out for you.

 

Also, DJ music, beer, food can be had there. Fish fry is great...full bar inside etc...Plenty of "sightseeing" as well :^)
Look for a Blue 68 Vette and a Black 55 BelAir. I'm usually sandwiched between them if we all arrive at the same time.

https://damascusshrinemasons.org/

 

1. A catalyst that old is no good to begin with. Has it been replaced?
2. The original equipment catalyst was a pellet-style. Hatefully restrictive, but once they rust internally, all the pellets migrate to the muffler. Once in awhile, you'd see a car shooting pellets out the tailpipe like a friggin' pea-shooter. There's a fair chance the "converter" is empty.
3. Stock valve springs? Why does he need "high zinc" oil when the valve springs are that weak?

The EPA went nuts on oil ingredients. They decided that zinc compounds would damage the converter on the severely-emissions-regulated engines, so the ZDDP level was reduced (NOT eliminated) from most motor oil. You could buy oil with the previous ZDDP level, but you don't need it.

What oil should you use? CLEAN oil, with a viscosity range as specified in your owner's manual.