pluggin' away

[RCC]

Hey TRS'ers,

Got a question about spark plugs in 4.0 motors.

I have a '97 Ranger with the big V6.
Changed plugs a few years back, no problem.
Other day I wanted to replace them again.
Went to local parts store, asked for same type/number but
they were out. Said that particular plug had been superseded.
Asked me the usual vehicle questions, did the cross check on
their computer, came back with the "compatible" replacement.

The new plugs have double the thread length of the ones
specified for my engine. Went around and around with the
"mechanic"/register jockey after I told him that was not
the one I need.
Showed him the MotorCraft OEM plug(AWSF42P) that I had
used last time. That one has very few threads. He kept telling
me it did not matter.

While the long thread plug would fit(they both the same shoulder height)
who wants a plug with half the threads poking out of the head?
Surely that has an affect on the heat range it was designed for.

Never got the ones I wanted.
Parts dude finally came up with Autolite 765AP.
They are short thread and truck runs fine.

Anybody know what the deal is about the thread length difference?
Is it due to changes when Ford went OHC with that motor?

RCC

 

[Big Jim M]

I THINK you are saying the plug you were offered would actually hang down deeper into the chamber.. If so it would NEVER WORK! It would heat up and not be able to eleminate it's heat into the coolant.. This would after a short while cause the plugs to become cherry RED with heat and they would ignite the mixture as soon as the intake valve starts to open.. The engine would cease to run at that time.. The results can become catastrophic.
Personally I would have insisted on the stock plugs...even if they must be ordered from a GOOGLE address.. Or at a parts house across town..
Big JIm

 

[RCC]

Hey BJM,

What you said is exactly what I thought when the
parts guy showed me those long thread plugs.
After I compared them side by side, the plugs are
the same length and the shoulder/seat where they
get larger is the same. That being said, the longer
thread style SHOULD stop when the shoulder contacts
the head. At that point, half of the threads would still
be exposed outside the hole.

What makes it so frustrating is these newer long thread
plugs(all brands) show as acceptable replacements for the older
short thread style. I don't think that's right.
Wish I had some pics to post so folks can see the difference.

I did find an article on a Ford FAQ site that warned those
with the newer OHC motors to NOT use the short thread
plugs. It went on to basically state 4.0's before 2000 use
those.

RCC

 

[RCC]

I managed to find pictures on the web of
Autolite short thread spark plugs my engine
uses and new long thread plugs listed as
interchangeable for 4.0 V6.

But, I can not post attachments. :-(

Oh, well.....

RCC