That is also incorrect. If you read my post idle time has nothing to do with needing a higher viscosity to maintain oil pressure. Sure 5-30 wont hurt anything but it is unnecessary. Look at what I said about the idle time conversion. The garage I work for services all the local municipal vehicles from Crown Vics to F550's. They all get Motorcraft 5-20 and most if not all those vehicles avg 3,500 idle hours within 4 years. The F550 V10 plow trucks will run for days non stop and idle on the off hours/driver break time. With the many many idle hours and very hard driving on 100 hour service intervals. Never once has any of the vehicles used anymore than 1qt of oil within the 3500 mile/100hr interval. All of the old squad cars later become taxis that idle more than before on 5-20. After taxi service they are usually sold again with over 250,000 miles on them running non stop for heat and AC, to the public who usually finish them off nearing almost 300,000,miles. My old F350 (in sig) was a former Wisconsin Central Railway service truck. The ODO had 160,000 miles on it when the motor went. Upon further digging into the truck I found out it had 7,580 idle hours on it so it is about 274,000 miles worth of wear and tear plus the 160k on the truck comes out to, 434,750 total mileage equivalent worth of wear and tear. I also talked to the service manager for the railroad who also explained that all their maintenance was done in house with Motorcraft fluids and filters including FL820s and Motorcraft Syn Blend 5-20. So I don't see where needing a higher viscosity is ever needed with modern oils. FWIW ford calls for an engine re-build or replacement at 8,000 idle hours.

 

That is what I switched to in my 2V V10 after the warrenty expired. Same engine a couple years prior the speced oil was 5w-30 but they switched to 5w-20 for CAFE. Nothing at the engines were changed.

The 5.4L Supercharged 4V Ti-VCT in the GT-500 specs 5w-50 oil.