In all the post I've read about vehicles achieving extremely high mileage I don't recall any that ran 5w-20.
I know 5w-20 is a fairly recent requirement, but can you imagine a vehicle reaching >300k miles with this weight oil?
I have 169K on a 2001 Crown Vic patrol car that has used Mororcraft 5w20 & Wix filters. It still runs strong and it is driven much harder than most any vehicles on the road. It won't see it hit 300K because I am slated for another vehicle on 2007.
Buzzsaw ..you would be about the only service to truly be "high mileage" with that oil. Didn't the stuff first come on the market in 2002? In four years how many drivers are going to be in "high mileage" territory?? Very few, IMHO. Yohan appears to be right on track with what would normally be considered a high/typical user ..about 15k miles a year.
That is, how do we define "high mileage" I'd say over 100k miles. Beyond that, it's like living past the 60's (considered a choke point) ..the odds are the same between 70-81 of your mortality rate.
The Milgard rep who came to our house to repair our windows drove an 02 F250 with the 5.4L Triton. It had about 170,000 miles on it. Serviced with either Quaker State or Pennzoil 5w-20 all of its life from Jiffy Lube, every 6-8000 miles. Didn't ask for further details.
2001 was the model year that all but a few Ford vehicles came factory filled with 5w20. Thus, if someone purchased a 2001 Crown Vic in the fall of 2000 that car has been on the road for 5 years.
And from what I've seen, the VAST majority of quick change lube places as well as independently owned repair shops do not offer 5w20 unless the customer specifically requests it. Most quick change places and shops around here use 10w30 in whatever particular brand they get in bulk.
A good friend has a 2003 Accord with 81,000 miles that has run exclusively on 5w-20 dino of various labels. I know this does not qualify as "high mileage", but I thought I'd mention it. So far, absolutely no problems with the engine.
I think that the jury would have to be out on this until you get 10 year old vehicles that have had this diet for their entire lives. Anyone who has higher mileage on a 5w-20 spec'd engine at this time is driving an "engine's dream" of constant state conditions (in the vast majority of users).
Even if the 5w-20 was doing a lousy job ..it still wouldn't be showing up in this type of use. The reduced wear ..even if elevated (I'm not saying that it is) would still be well below that which an "infrequent flyer" sees over the next 5 years seeing the same mileage.