I just saw a video saying he uses 20w50 oil in his high mileage engine. He said it will "fill" in gaps in the bearing journals and such. I have a 99 f250 4x4 auto 5.4 257K miles on it and I use 10w40. Should I be using something else? I think I am going to be beating a dead horse here but I had to ask.

 

"filling the gaps" is his personal opinion, not based in reality........... 20w50 is kind of thick for these motors.......... If your in the northern half of the country, 20w is thich enough in the winter to starve the motor of oil for a second as the pump trys to pickup the thick oil............. 5w or 10w is the spec.......... Look at youtube on what happens to oil pouring with 20w or 30w oil at ZERO ambient.

 

Too thick to run in an OHC engine.

 

I am not an oil expert but 5w-30 is what I would run in your truck. It's what I run in my 1997 f150 4.6l 220000 miles.

 

10w- 40 is OK for Texas ........ I would not use it in Minnesota....I believe 10w 30 would be better for you.

 

Use 10-40 high mileage oil. It has more zinc and will fill more imperfections than any increase in viscosity.

 

who told you there was zinc in automotive oil ? Zinc destroys catalytic converters.

 

The local Chevron distributor. He said the "High Mileage" formulas have a higher zinc content.
Just looked into it, motor oils still do indeed have zinc and phosphorus in them. The levels have been reduced with the newer LE series oils but its still there.

 

Years ago I fell for the thicker is better theory. I had a 79 400 with 4:10's, ran 20w50 in it. Oil press was good, until I watched one day. Running near 3 grand, my oil press was dropping and coming back up. Pulled over checked oil and was ok. Figured out when I was anywhere near 3000 rpm, oil press would drop and fluctuate. Short story was I had a melling hv pump and we figured it was pumping the pan dry because the oil was so thick, it couldn't get back to the pan quick enough. Swapped back to 10w40, no more oil pressure problem.

 

Why? Just use the specified 5w20 or 5w30 over 10 5.4 2v in the fleet well over 270k using 5w30, no oil consumption and run lije the day they left the factory.

 

There is zinc in automotive oil. Check out the analysis done on the virgin oils in all the threads in the link. They all have some amount of zinc in them.
https://bobistheoilguy.com/forums/ub...sis_-_PCMO/HDE