I would never consider 15W or 20W
oil in my Cobra engine. During a cold start, I want the
oil to actually flow to where it's supposed to go.
I have been using a 5W-30
oil for years. No problems maintaining oil pressure lap after lap. And the bi-annual tear downs don't show significant bearing wear. So it's doing what it's supposed to do.
Heavier oil does not provide additional lubrication if you don't need. It just requires more energy and more strain on parts to move it around. You need a thick/heavy enough oil to maintain pressure in all situations. That's it; more is not better.
Last year I was reading that a slightly higher hot viscosity oil will provide better lifter stability at sustained high rpm's. I tried a 10W-40, but can't really see any difference. This year I went back to a 5W-30.
There are only two significant advantages to a
synthetic oil - longer drain interval, and better heat resistance. If those two things are not important to you, use standard dino oil. Same results, less money.
A true
synthetic oil starts with a PAO base stock, no dino oil.
AFAIK, there are only 4 true synthetics on the market - and Mobile 1 is not one of them. The rest of the "synthetics" are really dino oils that have been refined enough to meet a marketing standard of "
synthetic". The dino oils don't hold up as well in extreme environments, like racing and air cooled engines.
The diesel oils were somewhat better for a while. The gasoline oils reduced the ZDDP because it can damage the cats. Diesels didn't have cats, so they remained unchanged. For a while. Now some diesel angines have cats, so the ZDDP was reduced by about 25%. Not such a big deal any more. Now many diesel oils also have a certification for gasoline engines. That means there's very little difference from the gas oils for our engines. I think the big disadvantage to the diesel oils is their 15W or 20W rating.
IMO, you should choose a motor oil with the following criteria:
1. A dino oil or true synthetic according to what actually need- longevity or heat management.
2. Keep the W viscosity as low as possible.
3. Maximum viscosity high enough to maintain pressure in all situations, and no more
4. One that performs well in actual wear tests.
But, that's just my opinion. I could be wrong.
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