Which thread sealer for leaking NPT oil fittings?
nobrakes - 14/7/16 at 06:00 PM
Went for an MOT today, (new fuel pump packed up on the way to yesterdays appointment, didn't even make it out of the driveway 
)
its the first run on the road with the new engine. The good news is it passed with no advisories, the bad news is that on getting back home I noticed
an oil leak.
Its a Rover V8 with this remote oil filter, not sure how to get the picture up so here's the link -
Fram HPK2 High Performance Remote Oil Filter Adaptor Mount Base
The filter housing is alloy with ½" NPT threads and my NPT unions are bzp steel.
I used ptfe tape but it isn't sealing, they're done up pretty tight I thought but I'm wary of overtightening and cracking the alloy so
want to try a liquid sealant.
Here's the question, which sealer? There seem to be lots, has anyone got any experience of whats a good one to go for?
ash_hammond - 14/7/16 at 06:09 PM
I did mine with PTFE tape on my old pinto oil cooler sandwich plate.
hizzi - 14/7/16 at 06:10 PM
ptfe should be fine did you use the thin water stuff or the thicker single wrap for gas? single wrap is better.
also are the threads tapered? if they are parallel threads then they should be sealed with copper washers.
nobrakes - 14/7/16 at 06:37 PM
I used the thicker stuff you mentioned, that's what was recommended to me.
NPT is a tapered thread, some of my other fittings are BSP parallel (not BSPT tapered) and came with Dowty seals which have sealed up fine.
I suspect the leaks may be because they aren't tight enough but daren't do them up any tighter.
The walls of the threaded holes in the alloy housing don't look to be very thick and I just don't know how much tighter I can go before the
taper thread will crack the alloy so some sort of liquid sealer has got to be the best way forward.
rodgling - 14/7/16 at 06:41 PM
Normal thread lock (I've used blue in the past) will work fine.
Chris_Xtreme - 14/7/16 at 07:12 PM
on my rv8, I thought it was leaking from the same place somewhere, but it turned out to be a slightly loose bolt on the pump housing plate, those
bolts with the odd head. it ran down so finely and then collected and dripped on the remote part.
just a different thought..
cheers, Chris
gremlin1234 - 14/7/16 at 07:34 PM
quote:
Here's the question, which sealer? There seem to be lots, has anyone got any experience of whats a good one to go for?
taper
threads were designed to be used without any extra sealer, just remove all the tape and try that
coyoteboy - 15/7/16 at 07:28 AM
Yeah I've never used sealer or tape on tapered threads and I've never had a problem. It would be my first port of call if I did have a
problem though. Strip it off and try without.
nobrakes - 15/7/16 at 09:26 AM
In an ideal world the threads would all be perfect and both parts of the joint would be the same or similar metal which isn't what I've
got.
Have a look at the alloy threads in the picture, they aren't very well formed.
As the steel male thread screws into the softer alloy female thread I don't think I'm getting the intended sealing action where the thread
crests and roots on both parts deform to fill the gap because the steel crest is cutting into the alloy root instead. So it leaks without anything to
fill the gap.
Tape usually seals but it isn't a 100% guarantee.
There are tolerances in thread dimensions, maybe the male & female parts of these 2 joints are at opposite ends and combined with a mix of steel
& alloy is giving me leaks?
FWIW I've just been and counted, there's a total of 16 threaded joints (to be fair, they aren't all tapered thread joints) around the
remote oil filter system and only these 2 oil filter housing ones leak.
I've had a look in Yellow pages and there's a hydraulics & pipe fittings place not too far away so am going for a drive out there to see
what they reckon - watch this space...
daviep - 15/7/16 at 06:29 PM
quote:
Originally posted by gremlin1234
quote:
Here's the question, which sealer? There seem to be lots, has anyone got any experience of whats a good one to go for?
taper
threads were designed to be used without any extra sealer, just remove all the tape and try that
That's an interesting fact where did you learn this?
To the OP Loctite 577 or 5576 are good.
Silly question but did you wrap your PTFE in the correct direction, clockwise when looking at the end of the fitting which screws in.
Regards
Davie
britishtrident - 15/7/16 at 06:38 PM
As alreday said a normal (that is non-permanent) grade of Loctite Lock & Seal or Stud & Bearing Fit is all that is required.
[Edited on 15/7/16 by britishtrident]
Mr Whippy - 15/7/16 at 07:37 PM
Might be excessively negative but looking at it, it's price and design I can't help thinking there's something that will fatigue, crack
and wipe out an engine....
gremlin1234 - 15/7/16 at 10:47 PM
quote:
Originally posted by Mr Whippy
Might be excessively negative but looking at it, it's price and design I can't help thinking there's something that will fatigue, crack
and wipe out an engine....
I'am sorry, but I must agree, just not well made
nobrakes - 15/7/16 at 11:19 PM
quote:
Originally posted by gremlin1234
quote:
Originally posted by Mr Whippy
Might be excessively negative but looking at it, it's price and design I can't help thinking there's something that will fatigue, crack
and wipe out an engine....
I'am sorry, but I must agree, just not well made
You've got me worried now, what specifically do you see as the problem area?
By the way, the hydraulics place didn't have any 577 left so I ended up with 243 instead - apparently this one works with light oil contamination
on the threads which is handy.
I removed the tape (yes, it was wound in the right direction) and re-assembled the fittings this afternoon so I'll see what happens after the
loctite has cured.
gremlin1234 - 16/7/16 at 09:20 AM
quote:
You've got me worried now, what specifically do you see as the problem area?
they are the only joints that you have made that you
are having any issues with. as someone said, if you look at the picture of the item, the threads could be better defined.
this wikipeadia page may help
https://en.wikipedia.org/wiki/National_pipe_thread
it suggests a lubricating paste or ptfe tape for assembly.
edit:
hopefully what you'd done with loctite should work well.
[Edited on 16/7/16 by gremlin1234]
nobrakes - 16/7/16 at 10:14 AM
quote:
Originally posted by gremlin1234
[quote as someone said, if you look at the picture of the item, the threads could be better defined.
this wikipeadia page may help
https://en.wikipedia.org/wiki/National_pipe_thread
it suggests a lubricating paste or ptfe tape for assembly.
edit:
hopefully what you'd done with loctite should work well.
[Edited on 16/7/16 by gremlin1234]
About the threads - that was me.
The thing with NPT is that its designed work when both parts are a similar material, as in both steel, both plastic etc so the thread crests crush and
deform into the roots on both parts to fill the gaps.
With one hard steel and one soft alloy fitting you just don't get this. It may still seal, it may not and in my case it hasn't.
I'm going to check for leaks after a run out tomorrow so it's fingers crossed that loctite does the job!
nobrakes - 1/8/16 at 06:24 PM
Its been a long time but after fitting the new engine I sent the v5 to Swansea to get it changed and its taken them since June to do it...
I got it back at last so bought the road tax today, went for a run and no oil leaks from the loctited threads 