1998 F150 4.2L v6

So I finally got the top of the motor back together and went to change the oil...

Back when I was buying parts, I picked up a couple of Wix 51516 filters from Rockauto (which directly cross-reference to Motorcraft FL-400-S, per the manual). Got under the truck, and removed a crappy little Fram, P/N "COR3614TLE". Went to put on the Wix, and the threads are different. Looking at the ends of the filters, it's obvious that the Wix thread size is a little smaller than the Fram.

Now here's where it gets weird....

The Fram "COR3614TLE" crosses over to a "PH3614", which is one of the most popular filters around... and everywhere I look, those filters have 3/4-16 threads. But also everywhere I look, the Motorcraft FL_400-S and Wix 51516 also supposedly have 3/4-16 threads.

WTH? How can every source of info say that two filters have the same thread size when they obviously don't, and more importantly.... why does my truck have what looks to be different threads than the manual and entire internet says it should have (even though the filter I pulled off it ALSO has 3/4-16 threads according to the cross-references)?

Grrrrr

 

righty tighty.....?

 

What?

 

Why not just use a Motorcraft and be done with it?
Just stick with Motorcraft. If I was your next door neighbor, I'd give you a few.

 

I bought the Wix because I've been using them forever (daily drivers and my race car), and I was ordering other stuff from the same warehouse. But... that's all irrelevant.

I'm trying to figure out why the Wix 51516 (or equivalent Motorcraft filter, or any other crossed-over filter) has different threads than the filter I pulled off this truck. I know there were metric vs. SAE threads on a couple of later V8's depending on where the motor was built (seriously? ), but all the references I can find for the 4.2L V6 (including the downloaded factory manual) only call out one filter... which supposedly has 3/4-16 threads. And yet here is my truck, with a Fram Core filter on it, with different threads.

 

I don’t think 3/4-16 and 22x1.5mm are easy to mismatch up. I don’t think you could confuse the two and have some thing that was close but no cigar. In this case, just use the one that fits right, I gues.