ORIGINAL: Lees07GT

I think maybe it has something to do with the variable valve timing which is oil driven. Whatever the case, why not be safe and use 5W-20 like Ford recommends?

ORIGINAL: Fourth Horseman


I'm not saying you're wrong, because honestly I don't know for sure. But I will say this: with every generation of engine that comes out I hear the same thing. I heard it with the 32v DOHC V8 in the Marauder. It went something like this:

Me: "I've run 5w30 for years in SOHC 4.6 V8s with no trouble."
Worried new Marauder owner: "But these engines are DOHC, with much tighter tolerances."

Yet, here I am 5 years later, having run Mobil 1 synthetic 5w30 in my Marauder, which gets flogged regularly and HARD, and it runs like a watch.

*shrug* Maybe there is something new in these 3V heads on our Mustangs that requires thinner oil, but I really doubt it. That said, if I begin to hear valve train noise or anything else odd I'll switch back to 5w20. Until then I'm going to go with the oil that I believe protects my engines better.

ORIGINAL: Lees07GT

The 4V 4.6 does not have Variable Camshaft Timing like the 3V does. VCT uses engine oil to control the camshaft timing. Also, Ford only recommends 5W-20 for the V8. They recommend 5W-30 for the V6. So something in the V8 seems to require a thinner oil. I am certainly not an expert on why Ford recommends 5W-20 for the 3V 4.6, but in my 40 years of owning and working on my own cars, I have found that following the manufacturer's recommendations on fluids and lubricants to be the prudent choice. The only time I have ever run into any problems was when I ignored the manufacturer's recommendations and used a thicker oil because I thought it was a better lubricant. I even remember reading an article in a car mag many years ago that suggested using the thickest oil you could get by with (engine would still start) because the thicker oils would protect the components (mainly crankshaft bearings) better. That was hogwash and obviously proves that you can't believe everything you read. Modern engines are more complicated, tolerances are tighter and oil needs to flow. It can't lubricate properly if it doesn't flow. IMO, no automaker in their right mind providing a significant warranty on their drive train is going to purposely recommend a lubricant that could eventually result in engine damage and undesired warranty claims.