first, I am not the most mechanically inclined, I'm not about to attempt pulling the valve covers off my 5.4 2004 FX4. Truck has about 107k miles, anyway just was listening to a mechanic talk about sludge, and got to thinking..... about 4 years of my truck (from 2007 to 2011) were used when I worked about 1 mile from my home, short trips daily, in hot and cold weather.

I have never missed an oil change, all done since truck was new, and 90% done right at 4k miles, a few less and a few around 5k. All with Motorcraft Syn Blend 5-20, and every change without exception had a new FL-820S filter.

So I shined a flashlight down into the oil fill, looked really nice didnt see any black sludge, a little varnish on the metal but overall I'm happy.

Am I missing where the sludge should be? even when I check the oil after 4k miles, looks pretty clean on the dipstick, just darker than new which I know is normal.

 

Sounds like you're good. On a sludged-up engine, you will see it when you open the fill cap - looks like somebody sprayed in there with asphalt. Normal 'browning' is no cause for concern - where you can still see the metal but it has a brown tint. You could start putting in a can of Seafoam or 16 oz of Marvel Mystery Oil a couple weeks before the oil change. BTW, I think the Motorcraft oil is about as good as it gets.