Graham,
I went throught the gasoline-compatible sealant issue recently
(looking to seal threaded joints in newly created fuel delivery
system; not stock). Here’s what I found:
Loctite 242 (blue) is a very common thread-lock (medium strength) and
thread-sealant that will not deteriorate when constantly exposed to
several types of gasoline (leaded, unleaded, etc., aviation). Same
applies to 242 and Ethanol (common gasoline additive in US).
see tds.loctite.com/tds5/docs/242-EN.pdf
Loctite makes several gasoline-proof sealants, but the above 242 is
the readily available blue stuff for thread locking. It will work
fine on your drain plug (see below).
I decided to use Hylomar HPF (now a Permatex product) as my fuel-line
thread sealant. This stuff is meant to be used as gasket dressing (it
is a gel), but works well when smeared on threads. Hylomar HPF WILL
seal againt all formulations of gasoline. I found a tube at NAPA, but
I’ve heard it has been discontinued. I wouldn’t recommend Hylomar HPF
for your use: It would work well, but is too hard to find - I think.
I am worried about some “less-than-perfect” thread matches in my fuel
system, so I am looking for “extra” sealing - slightly
above-and-beyond normal thread sealing.
Teflon Tape is actually a family of several products: some will work
perfectly, some will only be “OK.” Most will seal against gasoline;
all will allow thread release (at next tank draining - do it often?);
and (if used with moderation) will not produce globs of excess
material into the gas tank. If used without some thought, teflon tape
(indeed: any sealant) can produce thin threads that will wind up
clogging fuel filters, needle/seat or carb jets.
In the best-of-all-worlds, the tapered threads should be
self-sealing: metal-to-metal contact SHOULD seal. But … gasoline
tends to find any tiny imperfection in thread-form to leak through.
“Are we dealing with a fairly new threads?” you must ask yourself.
Any doubt should lead to use of a little teflon tape (or other sealant).
If you use any form of thread sealant, use very little. The
metal-to-metal contact will do most of your job and only a very small
amout of sealant will be needed (if any). That last little bit of
sealing goo will be trapped down in the interstices of the threads;
not exposed to constant flushing contact with gasoline - so most
thread sealants will probably work well. Whatever you do, do not
smear on globs of sealant. More is not better.
Use a little teflon tape (any type), some Loctite blue, etc., and you
will be fine. Rely on the metal-to-metal contact and use your little
dab of sealant-of-choice as a fill-in-the-small-chinks device. Or,
leave the sealant out entirely (at first) and see what happens. The
fuel tank is not that hard to remove, should things not be perfect.
Rich Boyd