5-20 or 5-30 motoroil?
 

Okay, I've heard both. Someone sale me on one or the other please.
I have a 99- F250LD 4x4 with the 5.4 triton w/ 200,000 miles. Seeing as
how I live in Georgia and it's 18 degrees right now I'm leaning to the
Motorcraft 5w-20w blend. With a FL 820s motorcraft filter. Then, when
it warms up in March or April, go with the 5w-30w. Someone change my
mind . With good info.
thanks

I use 10-40.
200k on it might need a little thicker oil than what your thinking about.

Sounds like a good plan to me. I run 5-20 year round based on some good used oil analysis I have seen on another site. Also, the Motorcraft quick reference chart specifies 5-20 for your truck, but if 5-30 makes you feel better in the summer, no harm done.

Doesn't really make any difference. The 5w number is the one that concerns cold flow properties. The 20 or 30 refer to warm flow properties. They are going to be almost identical in cold situations and the 30 will be slightly thicker than the 20 in hot situations.

5w-20 would be just fine year round. There is no need to go to a thicker oil. 5w-30 though is so similar that you will not notice the difference. Buy which ever is cheaper.

These motors need oil to get to the heads as quick as possible on start up. Which is why a thicker oil is not preferred. These are not old pushrod beasts of past which needed thicker oil.

FWIW I have over 200k on mine using only Motorcraft or Castrol GTX 5w-20 and Motorcraft FL-820s filters.

If anything stay away from anything that begins with a "10" or higher.

That's absolutely correct. Viscocity can be defined as: resistance to flow. The higher the number, the more resistance to flow. Multi-viscosity oils place the cold temp viscosity first, followed by a W for winter(not weight) and then the hot temp viscosity second.
Ambient temperature and resistance to flow are inversely related. This means, the colder the temperature drops, the higher the resistance to flow of oil. Changing from 5W-20 to 5W-30 for an advantage in winter therefore doesnt make sense. A change from 10W-30 to 5W-30 in the winter would make sense because, at cold temperature, the 5W has LESS resistance to flow and can reach vital engine parts faster on cold startup.
If the manufacturer calls for 5W-20 then use it.

Steevn, if you have 200k on your truck, I'd say just keep doing what you have been doing with oil! For me, I'm sticking with the 5w-20 my manual says to use on my '02 5.4.

You can run either one all year round, personally I am back to 5w20.

2 problems with using the heavier oil. One, increased oil drag, you may read higher pressure, but you get reduced oil flow to the critical parts like bearings. The oil will run hotter and break down more quickly, resulting in increased chemical wear. Two, you will get lower fuel economy, not by much, but it is measurable.

Stick with 5w20, your engine is designed for it. You mileage is irrelevant, even if it had half a million miles I would still run 5w20.