I just purchased a 1998 Expedition XLT 4x4 with 146K miles on it. In really nice shape. Has the 4.6L engine, it runs very smooth and pulls the big wagon suprisingly strong. I have read articles to use 5-20W oil in these motors because of tight tolerance in engine; my manual sayes use 5-30. Does it make any difference. Thanks

 

Use what the manual says to use.

 

You can use either.

Ford changed the recommendation to 5W20 a few years after your truck was manufactured. See TSB 02-1-9.

 

I use Motorcraft 5-20 semi syn. From what I've heard these motors aren't designed for thicker oils

 

The local Ford dealer (parts dept) here offers a $urprisingly good deal on an Oil Change kit that has the req'd # of qts [varies by application] of the Motorcraft 5W20 Syn Blend and a Motorcraft filter... I think it was le$$ than buying pure conventional oil just about anywhere else.

 

Wrong. See TSB. Ford's semi-syn 5W-20 wasn't yet approved when his (or yours, for that matter) truck was made.