Lotus Elan

Petrol Proof Sealant.

PostPost by: G4ILN » Sun Nov 05, 2006 8:49 pm

I removed the drain plug from my fuel tank whilst cleaning it out. It's a taper thread plug, so will need some sort of sealant. Apparently PTFE Tape dissolves in petrol. Hylomar Blue although petrol proof is not suitable for constant immersion in the stuff.

What sealant should I use? It needs to be something which is available in the UK.

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PostPost by: "Sean Murray" » Sun Nov 05, 2006 10:58 pm


I have removed and replaced the drain plug many times. I never used a sealant. It never leaks.

Sean Murray.

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PostPost by: fatboyoz » Mon Nov 06, 2006 1:44 am

There should be a sealing washer of some description under the drain
plug. Perhaps fibre, copper or some sort of crush washer.

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PostPost by: G4ILN » Mon Nov 06, 2006 3:41 am


This is a TAPER threaded plug screwed into a TAPER threaded hole.
Such threads are designed to seal on the thread, which means some
sort of sealant is needed.

The plug has a square head smaller than the plug itself, not a
hexagon head under which a copper or fibre washer can be fitted.

I might retap the hole with a PARALLEL thread, which will enable a
hexagon headed PARALLEL threaded plug to be used with a sealing


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PostPost by: "Clivey Boy" » Mon Nov 06, 2006 7:49 am

Hi Graham
PTFE is not effected by petrol. PTFE tape can go clear when used with petrol
but it still does the job.
If its a taper thread then it seals on the threads with tape or sealant. If
it is a parallel thread then it needs a sealing washer etc under the head.
Sean mentioned that his seals without tape, as the tank is not under
pressure it is quite feasible.
I personally would use tape as it helps sealing and also acts as a thread
lubricant for easier dismantling later.


"Clivey Boy"

PostPost by: Bill Barry » Mon Nov 06, 2006 7:54 pm

"There should be a sealing washer of some description under the drain

Not with a tapered thread plug!!

Bill Barry

PostPost by: lotuselan2 » Mon Nov 06, 2006 8:08 pm

I would use Permatex Fast Drying sealant; it is brown and funky but works
well on fuel if you leave it an hour or more to dry. I should be available
in UK; Permatex is part of Loctite now.

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PostPost by: richboyd » Mon Nov 06, 2006 10:22 pm


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 http://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

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PostPost by: mackmotorsport at aol.com » Tue Nov 07, 2006 12:06 am

It's very possible that you actually have a parallel thread there already
and someone has forced in a taper plug.The British seldom use them around fuel
and there is a close size in whatever thread that would be (not pipe but tube
fitting thread?) Someone here probably knows...
Bill Mack
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PostPost by: Fred Talmadge » Tue Nov 07, 2006 12:33 am

I just replaced my buggered gas tank drain plug, and it is brass with straight
threads and a fiber washer and a hex head. This is on a 1965 S2 with a stock

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PostPost by: lotuselan2 » Tue Nov 07, 2006 2:12 pm


I do not believe Hylomar is being discontinued. The problem is that if NAPA
doesn't sell 20 of something in a store everyday, they stop stocking it.
Other shops will have it as well as specialty dealers on line.

Note that it does not "setup"; it stays as a paste or gel in use.

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PostPost by: G4ILN » Wed Nov 08, 2006 9:50 pm

Lotus Elan Owners - Plus 2s to 26RsThanks for all of your replies.

I checked the thread bosses in the tank for the drain and banjo connections and found that both are tapped 1/4" BSP x 19 TPI. BSP = British Standard Pipe. The 1/4" refers to the internal diameter of the pipe and not the external diameter of the thread, which is more like 1/2". The bango connection has a parallel thread and the sealing is by washers. The drain plug connection has a taper thread requiring a taper plug which seals on the threads.

I'll be using loctite 242, as the spec sheet confirms it's petrol proof and it's easily obtainable locally.
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