Oil for my new to me 84 F150?

Joined
Aug 2, 2018
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862
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South Carolina
I got me a 84 f150 xlt 5.0L c5 auto. Truck has been well taking care of. Was wanting to change its oil and saw that the previous owner was using 5w30 but to me a flat tappet 5.0L would shear it out of grade over a 10w30. Truck also runs about 3k rpm at 65mph. Should I use RGT 5w30 that I have or use rotella t4 15w40 that I also have. My 88 truck seemed quiter on 40 than 30 but had more miles and used oil alot. What yall think?
 
Joined
Dec 19, 2019
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Muncie, Indiana
Maybe use what he was using but in a 10W30.
RGT is only available in 0w20, 5w20, and 5w30, plus I have this suspicion it's gonna be discontinued soon since retailers haven't seemed to really unload any of it since it was introduced about 2-3 years ago and I've only really seen anything about it because people were buying it on clearance.
 
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10W-30 or 40 would work I would think. I personally in something that old would use 10W-30 or higher but that’s just me. As stated above possibly ask what brand of oil he used and get it in a 10W-30 formulation. If you have a service manual or owner’s manual for it that might give you a table that shows the climate type and which type of oil to use. In my 1994 Ford 5.8 I use 10W-40 year round.
 
Joined
May 21, 2018
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My situation: 1993 F150 4.0L E4OD 255K miles. Originally spec'd 10w-30 but back spec'd to 5w-30. Using 5w-30 (SuperTech Syn) and Motorcraft filter. No problems, no perceivable oil consumption.
 
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Dallas,Tx USA
Me,personally,I don't believe in back specing. I guess it's because I'm one of the "thickies" here on BITOG and I normally use the thickest oil per FSM.
 

OVERKILL

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That engine has a broomstick cam and light springs, you aren't going to have issues regardless of what you run. if it isn't consuming on what the previous owner was running, I'd be inclined to just stick with that.

That said, I usually run M1 0w-40 in my Windsors and it definitely wouldn't hurt here.
 
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Dec 19, 2019
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6qts sounds like a pretty typical sump size on a V8 truck, what's ridiculous is my TrailBlazer the straight 6 in that thing holds 7 freakin quarts.
 
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