What Oil Viscosity for Southern California Car?

I've never looked at a manual for my car (1990GT) but i've been running Valvoline Restore & Protect full synthetic 5W-30 and am in San Diego.

Did not know our cars take 10W-30 from the factory.

fasterthangas said:

So the recommended 5w30 is even better today, correct? That makes the factory recommendation even more valid.

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The recommended type of oil in 5.0 Mustangs was 5W30 in colder climates and 10W30 in warmer. Being 5W30 started seeing the market around 1985 there have been a lot of improvements like all lubricants.

fasterthangas said:

For reference, my 11:1 363 that regularly sees 7000rpm in Phoenix heat uses 5w30 semi synthetic oil. This is the oil recommended by Driven Oil techs and my builder. Taken into consideration was ambient temps and bearing clearances.

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I've followed your build and its really nice and one hell of a motor for sure.

For reference even thought it is irrelevant the Coyote motors use 5W20 and some other motors are using 0W20 these days. The 331 in my Coupe likes it above 7,000 rpm and it gets 10W40 Brad Penn per the engine builder's recommendation. None of this really matters in this discussion because the OP has from what I can tell a stock 86 GT.

What I was trying to point out (and may have done so poorly) is things have advanced so do some research to see what is best for what appears to be a stock build, 85,000 mile, 40+ year old motor with today's oils.

Yup. I didn't bother mentioning summer weight but it's not really important these days. Like stated, oil is so much better now so I believe he'll be just fine. As a matter of fact, I recommend Walmart Supertech synthetic changed every 5000 miles. It's actually quality oil for a stock motor. These cars were capable of 200,000 miles plus while using the oil from 40 years ago.

I had my struggles with this engine but it's now running great and I can finally enjoy the car.