The Seal Deal


Please recommend a high quality thread
sealant to use on the head bolts of my 1986
W250’s 318. The decal on the valve cover
makes it sound like this is important.


I have never used anything but light oil,
so that sticker really threw me a curveball.
Sure enough, I did find some reference to
sealer application in some 80s FSMs (but
not all). No mention as to why, though
you’d have to assume at least some holes
were wet (into the water jacket). I typically
have at least a few 340 or 360 blocks lying
around but have none at the moment to
inspect. Anyway, I put this by Chrysler
Engineering, including several retired
guys, and one current who is one of the
sharpest individuals I have ever met – Dick
Winkles. The following is a synopsis of his
and their – answers:
One engineer mentioned that his 1980
service manual recommended Mopar
Lock N’ Seal, P/N 4057989, and a final
torque of 105 ft-lbs., yet another one
wrote: “ I have a 1980 Dodge Truck service
manual and it doesn’t say to put anything
on the threads at all. It does say to “Coat
new gaskets lightly with number 1057794

[Mopar Perfect Seal, a gasket cement]
sealer and install on cylinder block. Then
install cylinder head bolts, torque to 50
ft-lbs, then 105 ft-lbs. No mention of thread
sealer or oil on the threads.”
Another said: “…Teflon sealer on the
head bolts. He should also look very
carefully at the block deck between the
head bolts and the water jackets because
those blocks liked to crack. Can’t really
remember what years these blocks were
used. With the heads off you can see that
the bolt holes are wet. With the engine
assembled I don’t remember if there is
any tell-tale signs other than the decal.”
Another fellow wrote back: “I have a 1983
318 that I recently rebuilt. It’s true. The
head bolt bosses, all but a couple are wet.
I couldn’t believe how many were wet and
[that] we would do such a thing, but we
did. We had a program back in the day to
make a lightweight LA engine block and
the head bolt bosses were reduced to take
weight out and they were through and wet.
I experienced this first hand with a 1983
318 engine.”
Dick himself wrote: “The light weight
‘A’ engine, or ‘LA’, had wet head bolt holes
other than the race and T/A blocks. In a
perfect world, the ‘LA’ head bolts didn’t
technically need sealant since the head
gaskets sealed around the head bolt anyway
– so it wasn’t recommended for many
years. Rather, oil was used to achieve a
more accurate torque reading. Sometime,
maybe late 70s or early 80s, sealant
was recommended to probably reduce
the possibility that coolant could get by
the head gasket and leak internally to the
crankcase or externally (the EPA/CARB
may have had a hand in this to reduce the
chance that any coolant could be lost) to
the environment. In my opinion, I’d use the
sealant. Just be mindful that it will affect
the true torque reading, I’d probably use
a high side head bolt torque like the 105
lb-ft number since sealant will have higher
turning friction than oil.”

Basically, I concur. The sealant will do
no harm if it is superfluous, and could prevent
a coolant leak if it is, in fact, needed.
Interestingly, one engineer looked up
the part number of that sticker and said
the first year it was used was 1989!

The mystery valve cover decal.

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