I would like to use 0w20 due to short trips, but there are occassions where the car will see 100f temps on the highway and also in stop and go. 0w20 is not Ford approved. Is it because it is a little too thin, a little too low on hths and a little too high on noack?
Basically, 5W20 and 0W20 should have the same viscosity properties in the entire temperature range, except for freezing temperatures. 0W vs 5W only tells you have 0W oil flows better in freezing temperatures. Most manufacturers publish the kinematic viscosity of oils at 40C (consider that start up temperature in hot summer). The 5W20 and 0W20 should be about the same. Once warm enough, the 5W20 and 0W20 also should be about the same (the 100C viscosity is also provided in the data sheets). Considering that you live in California, 5W20 should be good enough unless you prefer a certain 0W20 oil for other reasons. Some manufacturers now recommend 0W20 for new cars. I think this is driven by desire to have a single recommendation for all people, those living say in Minnesota and California.
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Will using 0w20 or even 5w20 compromise my 1 year oci seeing that Ford specify 6 months on 5w20?
Only used analysis will tell with certainty. Fortunately, there are many reports for 0W20 in used oil analysis section on this web site. A lot of people don't like the 0W oils because it is believed that they don't extend as far as 5W oil. This is because 0W20 may need more viscosity improves, which may wear out with time faster.
I think car driven in 100F on the highway should have no problems with cooling engine due to good air flow. It's the city driving, specially stop and go that may cause the oil to be a bit hotter. Again, it's hard to say with certainty if you need 5W20 or 5W30. I'd pick a high quality 5W20, run 5,000 miles and send a sample for analysis.