Which of these synthetic oils (Schaeffer's, Mobil 1, Mobil Delvac, Redline, and Amsoil) do you consider to be the best synthetic oil (of course, Schaeffer's is available as a part synthetic and a full synthetic)?
In terms of specs. I think the orders is: Redline, Amsoil, Mobil 1, Schaeffer's.
They are all good. For racing and high performance I think Redline. For the Money Mobil 1 and Schaeffer's. For extended drains Amsoil, (regular 5w/10w-30.
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Delvac 1 is in a different class but is one of the best oils money can buy....so they say.
Personally I consider best as:
1) Lowest engine wear in ppm/mile
2) Lowest varnish/carbon/sludge it leaves behind
3) How well it holds up over the drain interval
I think you can't go wrong with any of the oil you mention. Each might shine over the others in a particular application but I think those are the best out there.
In the summer I look for a 5W40 with the highest flashpoint, in the winter a 0W30 or 0W40 depending on which part of the country I'm in. For use in a engine with a highly loaded valve train XXW50 all year round. Then I shop around for the best price from an oil company or brand that I recognize, not caring whether they are a group III or PAO product.
I have started using M1 in winter only because of its excellent cold starting properties. I feel a good group II or II+ dino (Chevron/Havoline) is fine for the rest of the year for my application.