Scored an 82 brat with turbo!

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MilesFox's advice of 5w40 over 5w30 in a turbo motor is sound. Built or high mile motors might even prefer 15w50 racing oil with lots of zinc and phosphorus.

 

0W40 is actually thicker at 210F than 10w30, the first number is for winter grades.. Which is directly effect by how much pour point depressant additives are in it. Think of it like something they put in to keep the oil fluid at cold temperature, but the actual viscosity at 210F is unchanged. Consider the second number as oil film strength, what really matters when the engine is running for any period of time.

Not all synthetic labeled oil is synthetic either these days, some is just the same petroleum oil with sulfur removed.