RP 5w-20 in newer F150

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Jul 31, 2003
I just wanted to get some opinions here. Since new in 2001, I have always run 5w-30 synthetic in my 4.2L V6 F150. Mostly M1 and Royal Purple. The recommended viscosity is 5w-20, however in 2001, 5w-20 was hard to come by. That was my reasoning at the time for the change. So with rising gas prices and my quest for better mileage, I have decided to switch to 5w-20. Saturday morning I changed the oil to Royal Purple 5w-20. So far I notice a bit better mileage, but can't really quanitfy it yet. Anyone think that this may not be a great idea at 80K miles? Should I let this run for 5000 miles and then do a UOA?
I think any GOOD synthetic should hold up well to 5K. I mean, if it didn't, why pay all that extra bucks for it and use a good dino oil. Like you, in '01, 5W-20 was not common, so I ran with the 5W-30 and never looked back. All is good so far and running the M1 5W-30 in both my 5.4l F150 and 3.0 Accord.
I'd think a good synthetic 5w30 would give almost the same mileage as a blended 5w20. We're talking 10ths of a mpg.
I don't know. My truck is acting kinda funny now. At idle in drive, it vibrates and sounds like a faint knocking sound, when fully warmed up. When its cold, it runs smooth. Accelerating swiftly is more difficult now, but cruising seems easier. I hate to dump oil that has 500 miles on it, but don't want to damage my engine. Plus I will be driving some long distances this coming week. Anyone think I should try to thicken this oil up? Dump it? Run it another 2500 miles and test?
Oh BTW - my mileage was only a little better. I'm getting a litle over 300 miles per tank, where as before I was averaging 270-280 miles per tank.
If it were my truck I would dump it and save it for your mower or something. It sounds as though the 20 weight is to thin for you. I'd go back to a 0W30 or 5W30 oil.
Another thing to consider that might perhaps help keep this in perspective: Ford's motivation for recommending 5W-20 vs. 5W-30. It was to help themselves comply with the federal CAFE regs. The mileage gain is indeed very small on a per vehicle basis, but when multiplied across the thousands of vehicles involved, it looks good for Ford. On the other hand, it does what for you? Do you think that either Ford or Honda made any mechanical changes to the engines involved? No! They want you to use this oil so that they can make their numbers. Obviously, they really don't care at all what happens to you or your vehicle when you get into the six-figure mileage range. I will say this: although I'm deeply suspicious of oil this thin, I'll reserve judgment until I see some more objective evidence of what's going on inside and engine fed 5W-20, so for starters, do a UOA if you do leave the oil in for any length of time.
Originally posted by KW: If it were my truck I would dump it and save it for your mower or something. It sounds as though the 20 weight is to thin for you. I'd go back to a 0W30 or 5W30 oil.
I agree with KW except I like my lawn mower and wouldn't want that thin oil in it either...... Sorry for being blunt but my new 2003 CRV engine which calls for the 5w20 is running much smoother and quieter with the new Mobil-1 0w30 R in it. Same with my Accord running the new 5w40 truck/SUV oil. I've read all the arguments on this and am of the conclusion it's not a good idea to go to one extreme or the other. Too thin or to thick. If I were you I'd just stick with the 5w30 you were using. Especially with summer coming up...
This has been a good topic of discussion for some time on this board and I have always agreed that thicker is better. But, on the CAFE thing, I read one point that Fords may have CAFE troubles but HONDA definently does not. I can't buy the argument that Honda adapted to the 5W-20's strictly for CAFE purposes.
For what it's worth our 2001 f-150 7700 has a duel fuel 5.4 v-8 and has had oil changes with dino 5w20 at 3k since new and have seen no ill effects,even at the hottest part of the summer...FYI [I dont know]
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