Living north, with a very cool running 2.1L, which ran perfect for 10 years
while using Total 10W50 Oil.

http://www4.total.fr/middle-east/PDS/Auto/Total/QUARTZ%20RACING%2010W50.pdf

Last year I switched to Castrol Edge 5W50, and this is the first time I've
had issues in the spring with engine noise and stalling.

Once I do a mechanical review, adjust the lifters, and make sure valves are
not sticking & push rods are good.

And run a motor oil flush.

I'm thinking of going with 10W40, Liqui Moly - German Made Oil

https://www.fcpeuro.com/products/10w-40-motor-oil-semi-synthetic-5-liters-li
qui-moly-lm2043

With only 70k original miles on the 1991 motor. I'm thinking of trying the
following combination.

To help with viscosity.

https://www.fcpeuro.com/products/viscoplus-for-oil-300ml-liqui-moly-lm20206

May consider adding.

https://www.fcpeuro.com/products/hydraulic-lifter-additive-300ml-liqui-moly-
lm20004

Plus FCP Euro provides free lifetime warranty on all items, including
consumables, that can be returned, including oil!

https://www.fcpeuro.com/page/lifetime-guarantee

Jack R.