can i use 10-40 in my 91 f150 V8 5.0L
 

I wanna know if i can use high milage 10w 40 for my 1991 F150, its a v8 5.0L

that's what I use in my 1990 302~~~~have been for over 8 years now -she's a leaker }>

how many quarts should i use all 6 or 5 and a half, mine leaks too, i gotta do my rear main seal

Use 6. And of course you can use it. It's just a little thicker at operating temp than 10W-30. Same thickness at startup.

My Supra has 10W-40 in it right now, and calls for 10W-30. Used it after someone said it'd help with the lash adjuster (lifter) noise. The 5M engine is known for being noisy and the thicker oil helped quiet it down.

Thicker oil harder to pump more work for the engine and more protection. Thinner oil the opposite.

for summer that is fine but not for winter in ny.

USE 1 QT of Lucas oil stabilizer w/ whatever oil you use!

I've never added anything to any oil I've used. Lucas is some thick stuff, maybe it does it's job better than just upping your oil weight, maybe it don't. I haven't used it. But the folks that use it and Slick 50 and the like swear by them haha.

I'm gonna pour seafoam in my oil and drive about 50 miles before draining it, and see what that does, and that'll be the first additive I've ever put in my oil besides what comes in the quarts of oil themselves.

Use 10-40?? Go BIG!!
 

1995 F-150, 155k for miles;
5.0, Auto, 2 wheel drive.

In the Winter (in Southern California) I use 6 qts of Castrol 20-50, and for the Summer, trips to the Desert, etc, I use Valvoline Racing 50 wt, 5 qts with a measured top-off of Lucas Treatment.

Change the filter ONLY, fill the new one with LUCAS, and continue. I only change oil 3 times a year. No rattle, no lifter tick cold, and I'm hoping for another good year. This is my Company Truck, and Home driver too.

Bearings get worn; Motors get hot. I have 33" BFG's, and didn't re-gear. (my fault) But she still starts and runs quiet, thru the muffler!