Just bought a new F-150. 4.6 Liter V8. The owners manual recomends 5W-20. This seems to be pretty light weight oil. I hear that Ford did this for fuel economy. I am wondering if this will cause the motor to wear out quicker.

So far I have changed the oil at 300 miles with Castrol 5W-20, and a Fram filter. I plan to break in with regular oil, then switch to full synthetic.
Should I stick with 5W-20 and then go to Mobil 1 0W-20? Or should I go to Mobil 1 5W-30?

Any suggestions?

I use Havoline 5W30 and Fram fiiters every 3K miles in my F150. Just turned 216,000 and still going strong.

I have a 97 F-150 with the 4.6 V8 and it calls for 5W-30. Almost 95K on the clock and knock on wood not major problems. I too though it was a light weight oil, but there are thousands of trucks out there with 100K, 200K, and even a few with 300K on them with minimal problems. check out [URL]www.F-150online.com[/URL] all your questions can be answered there.

The dude at the oil place told me it would void my warranty if I didn't use it.  I dont know if that is true or not but its better safe than sorry.

I used Mobil 1 0w30 in my 2001 4.6L Mustang GT, now I'm using Amsoil Series 2000 0w30 both flow faster at cold temperatures and protect better at operating temp than 5w20.  My EPA sticker that came on the window says 18mpg City  and 25 hiway, but I get 29 on the highway with the AC on so I must be doing something right.  I'm going to be putting on a Amsoil bypass oil filter soon that supposed to filter down to 1 micron.

PV74,

I have a 1999 F150 with the same engine as yours.  I have used 5W-30W Mobile 1 & Castrol synthetic after the first 1000 miles.  I have heard that the newer cars are using thinner oil because it lubes well and in addition, it removes heat better from hot spots... (makes sense to me).  

I pull a boat and it gets pretty hot in Central Texas.  FWIW, this is the third vehicle I have used synthetic with.  I ususally change the filter every 3500 miles and the oil every 3500 miles or 6 months... whichever comes first.   Never had any problems, but to be fair, when I used the same change schedule with regular Havoline or Castrol, I never had any problems either.  

THIS is the way to go.  Even if you don't go to the trouble and expense of an Amsoil bypass system (excellent idea), Amsoil filters are some of the best, if not THE best filters out there.  Amsoil oil is the best, bar none.  You will not void your warranty with Amsoil 0w30, 5w30, or any other oil that is not in a weight range drastically far from the manufacturers recommendations.

If you want to go a step farther in protecting your motor, see [url]www.filtermag.com[/url].  This product works - have seen the results with my own eyes.  Have the HD model on both my family's vehicles.

I'd stick with whatever oil the factory recommends, but I'd also be thinking about installing a good oil cooler*. There's nothing wrong with running thin oil, as long as you can keep the temperature down to where it performs properly.

*Up north, a thermostatically-controlled or oil-to-antifreeze cooler would be the way to go. Down south, the weather never gets cold enough to make oil overcooling a consideration.

I have heard about Amsoil. I was wondering if the claims had any truth to them. 25,000 miles without an oil change (with their bypas filter)seems to be stretching it just a bit. Changing the oil at 3,000 miles is almost a religous ritual for me.

The cost savings in oil changes would pay for the cost of the kit though.

Oil really doesn't wear out anymore, the additive package does.  With a 25/35K oil change.  You still test it every six months or annually.  Tractor Trailer drivers have done this for years.  My friends new Mercedes-Benz S430 has a system on it that tests the viscosity, pH and amount of dirt in the oil etc.  And his first oil change wasn't needed until 10K.  BMW has a similar system.  Pat Goss of Motorweek put a bypass oil system on G.Gordon Liddys Duramax diesel engine and he said the oil stayed so clean at 14K that he though G. Gordon had changed it.  Diesels oil usually turns black within a month of changing it.