Which is the better 5w-40?

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May 9, 2003
Fayetteville, NC
I'm sort of interested in switching to a 5/40 syn(but not 100% decided on it) for the summer from the GC, after getting my UOA done on it. Which is the better 5w/40 syn? and for which reasons? 1) Castrol Syntec 5/40 or: 2) Mobil 1 SS Truck/suv (my Walmart carries it now for 4.77 a qt) and where can one find the Syntec 5w/40? the local AZ carries GC, but not this.. BTW: car is 97 T'Bird 4.6L mod, 94k miles, driven daily; 60% hwy, rest city. I MIGHT do extended drains, if the GC uoa is ok. [another"?": Can i use GC for 5k miles or so for the 1st time, and do a UOA, or should I be safe, and get it at 3k miles?] Thanks in advance. [Smile]
My vote would go to the mobil SUV between the two you named. Although you may want to check out redline and amsoil 5w40's as well. 5k should be no problem for an initial run with GC in a properly tuned engine. [Smile] [Cheers!]
We are all familar with 5W40 SUV because it is rebaged Delvac-1. Delvac-1 has a great reputation and has been throughly torture tested in the comercial diesel areana for years. Castrols Belgium 5W40 syntec is the new kid in town. I doubt that it has been as thoroghly tested and tortured as Delvac-1 has. Castrol is also a hard company to trust! They have a history of playing bait and switch! If true synthetic is the name of the game look at Redlines 5W40 and you might look at Amsoil as well. Delo makes a Group III 5W40 and Rotella T Synthetic is group III as well. With all of this I think I would stick with M1 SUV 5W40.
Thinking of switching to Mobil SUV 5-40 also..been an Amsoil user for many years, always thought it was better than Mobil. But for the price and quality of SUV 5-40, you can't go wrong either way.
Forget 5w-40 Syntec. It is ok, but old. Currently using it in my wife's car...works well. M1 SUV is the way to go though. BTW- 5000 miles on GC is a joke, I just dumped my 3rd fill of it at 9000 miles. Also, my buddy who uses Amsoil in his big truck, literaly ran out the door for an oil change when I showed him the M1 SUV!
I was thinking of switching to the M1 SuV 5W-40. Just became a P/C for Amsoil, and was going to start using the AFL-5W-40 in my wifes new 2004 Axiom. I have just read that the M1 Suv might be their best oil on the shelf. Wondering to myself if a 5w-40 would be a good recommendation for a new auto that recommends 5w30 for winter and 10w30 for summer? I might also wait it out until some good test results come in from both these oils to make a choice..
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