Engine decking issue(help)

66fs said

I never understood this. I have always run 20w-50 or straight 30 in anything from a 64 Barracuda to a 96 Neon to a 2001 Jeep Cherokee. Hundreds of thousands of street miles in FL, SD, MD, SC. Hardly any wear on any part and the motors run like new for ever. I also get better mpg than most people. Isky says not to run thin oil on flat tappet cams. I'm not buying the thin oil argument in the everyday street world. Just food for thought...

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There is never a reason to run a single grade oil. Ever. As to the 20w50, it depends. If you like loose bearing clearances, and you run full groove bearings and a standard pump then maybe that heavy oil is good.

Heavy oil flows less, cools less (a big deal) and requires more clearance to do the same work as a lower grade oil.

That's why there is a benefit to heavy blocks that don't move around, rods that stay as round as possible, and a quality damper. If you do that, you can loosen up the clearances and use a 5w30 that will flow and cool better.

As an exception to the above, if you are running alcohol based fuels everything goes out the widow. People either forget or don't know, oil is the number one thing that seals the rings. Depending on the power level you may need a 50 grade (or higher) oil to seal the rings. And never use a Group IV or V oil with alcohol based fuels.