1999 Ford F150 automatic 249317.9 miles. 4.2 liter V6. I've always used 10 weight 30 synthetic blend notice on the Web there is a service bulletin to use 5 weight 20. Which motor oil weight should I used.. Thanks
If it were my truck, I would use synthetic blend 5w30.
5W-20 is correct weight but at 250K miles changing to a thinner oil might not be such a great idea. Any leaks going on now?
It does have a slight leak at the rear main seal if I drive over the of 75 only need to and about an half of a qt.
Meant to say over the speed of 75 and only have to add half a quart every month
Yea, a leaking rear main seal is typical for those engines at that mileage. No big deal really but 5W-20 could make it worse because its thinner at higher temps. I would also recommend using 5W-30 synthetic blend in your situation like @doc suggested. You can always switch back, but there shouldn't be any reason to. Good luck.
Seems like everything's going to full synthetic but it hurt to go to the full synthetic like a 5 weight 30 or 10 way 30
No, it won't hurt. Ford recommends synthetic blend for those engines now, because Motorcraft discontinued conventional oil which was the original spec back in the day. Full synthetic offers better protection than either. A high mileage full synthetic 5W-30 would be my suggestion there. Brand doesn't really matter but I hear good things about Mobile 1 high mileage full synthetic.
Thanks for all the help I went with the full synthetic mobile 1 5w30 and a wix filter
Good choices. You're welcome.
I found a TSB from back in 2003 backward spec-ing the 3.0 Ranger to be 5W-20 compatible as well after I accidentally mixed up the oil weights between my 2017 Mustang and 1999 Ranger. I put Pennzoil Platinum 5W-20 in the Ranger and was going to drain and refill it with 5W-30 high mileage Pennzoil Platinum I normally use until I saw that TSB. I would stick with the heavier weight oil in these old Ford engines with high mileage. I have 274k miles and usually go through around a quart or so every 5,000 miles, and I noticed on the thinner oil I went through a bit more on a 4,000-mile change. I don't have any noticeable leaks, so I assume a little more got around the rings and burned. I changed back to 5W-30 weight.
