Originally Posted By: jaj
Originally Posted By: Atomic
Thanks for the info everyone. Again, I want to state I will absolutely be using 5w-50 to maintain warranty.
That said, it sounds like the 5w-50 shears and gets beat up quickly. I don't know how aggressive the oil change light is on the Focus RS, but on my prior ST it would go 10k (I changed much earlier).
Would you recommend a shorter interval on the Motorcraft if I go that route? Is Redline in this weight good for 10k if the indicator light goes that long?
"Motorcraft 5w50 shears!" is an internet meme that's been flogged relentlessly as a means of creating fear, uncertainty and doubt about an excellent product that works really well, mostly for the purpose of creating demand for other excellent products that work really well. It's true that Motorcraft 5w50 shears down fairly quickly to a 40 weight viscosity, but it's also true that there's no evidence that the shearing affects its performance or the performance of the engines it's in.
Ford puts this stuff in every sport and racing engine that they make, and the roads (and forums) are NOT littered with broken-down GT, GT500, Boss 302, Mustang GT Track Pack and GT350 engines because of it. So, while the analysis reports indicate that it shears, apparently Ford doesn't think it matters and there isn't a shred of evidence that it makes the slightest difference. This reminds me a bit of the way that Castrol TWS 10w60 sheared in BMW M engines. 300 miles and it was down from 60 to 50. Worked fine for 10,000 miles just the same.
So, use the Motorcraft 5w50 the same as you would any other high quality engine oil - if you'd change it at 1/2 the normal interval, then do that. If you'd normally run the full OLM interval, then do that.
The UOA results that I saw on the MC 5w50 on a prominent Mustang enthusiast site showed that it sheared to a 40-weight within 1000 miles of street use, and to a 30-weight if the car was run in a track day. So if Ford is unconcerned about it shearing that badly, why bother specifying a 50-weight at all?
Get the AMSoil that meets the Ford spec. It will probably shear much less than the MC.