Drain plug question - what actually is leaking, threads or mating suface washer to pan?

TiGeo

TiGeo

Thread starter
Joined
Nov 5, 2009
Messages
10,248
Location
Virginia
I get weeping from the drain plug on my VW MK7 Golf Sportwagen. I have an aftermarket aluminum oil pan that uses an aluminum magnetic drain plug and single use aluminum crush washers. The recommended torque is ~20 ft lbs. Is the weep/leak from:

1) The threads (so you would say use HD teflon tape on them).

2) The mating surface where the crush washer should deform (I think?) to seal the drain plug against the pan.

Do I need to just tighten up (litterally!) and get that crush washer more deformed/tighten it more?

Don't forget folks, this post is set up on the forum using the "question" format so you can vote for the best answer with the arrows off to the right of folks' responses!
 
Last edited:
Sort by date Sort by votes
930.engineering said:
Which exact "aftermarket aluminum oil pan"? American made or far east?
There's some chance the mating surface isn't at an angle of 90 degrees to
the bore and thread. Next, your not so soft Al washer couldn't compensate
for the present deviation.

View attachment 254287
.
Click to expand...
I think @930.engineering has nailed the cause and offers an ideal solution using the washer type in his message.

That and use the new steel drain plug you have.

Scott
 
Upvote 2 Downvote
Oil drain plugs have cylindrical threads - at least the ones I know. Properly torqued tapered threads like those found on, for example, oil pressure sensors, make for a leak-proof seal. With a threaded oil drain plug with a malleable washer the onus of establishing a seal falls on the washer and the four mating surfaces. The washer is supposed to be soft enough to conform to minor surface imperfections and to compress a little, establishing a seal. I would closely inspect the drain bolt hole surround for imperfections like a deeper gauge or scratch as well as the washer contact surface on the drain bolt. If the drain washer has been reused repeatedly it may have become annealed and no longer be malleable enough to make a sufficient seal.
 
Upvote 1 Downvote
vavavroom said:
Oil drain plugs have cylindrical threads - at least the ones I know. Properly torqued tapered threads like those found on, for example, oil pressure sensors, make for a leak-proof seal. With a threaded oil drain plug with a malleable washer the onus of establishing a seal falls on the washer and the four mating surfaces. The washer is supposed to be soft enough to conform to minor surface imperfections and to compress a little, establishing a seal. I would closely inspect the drain bolt hole surround for imperfections like a deeper gauge or scratch as well as the washer contact surface on the drain bolt. If the drain washer has been reused repeatedly it may have become annealed and no longer be malleable enough to make a sufficient seal.
Click to expand...
I replace the washer each time. I am going to take a good look at this mating surface next go around.
 
Upvote 0 Downvote
TiGeo said:
View attachment 254278
Click to expand...
Looking at your new steel drain plug bolt - that's not many threads considering it's screwing into an aluminum pan. Using an aluminum bolt might make the thread interface even more suseptical to over tightening. I wouldn't use any more torque than what's specified, and even then I'd be careful.

So long as it doesn't drip when parked or oil mist the undercarriage when driving I'd let that drain plug weep its little heart out.

Scott
 
Upvote 0 Downvote
Never had much luck with aluminum crush washers providing a good complete seal unless the bolt and mating surface were of a considerably harder material than the washer, ie; steel. It takes a good amount of force to deform them sufficiently, and if all components are of similar material/hardness, likelihood of stripping either bolt or mating threads is much greater. DO NOT try and torque your way out of this one. Get a softer gasket/washer like the Elring ones @930.engineering posted. I have a big bag of them in 3 different sizes and use them on all drain plugs. Never leak a drop. Now the old seals everywhere else? Well, thats a different story 😁.
 
Upvote 1 Downvote
930.engineering said:
Which exact "aftermarket aluminum oil pan"? American made or far east?
There's some chance the mating surface isn't at an angle of 90 degrees to
the bore and thread. Next, your not so soft Al washer couldn't compensate
for the present deviation.



Keep using ~20 ft lbs please because aluminum pan thread.




I'd bet it's both. ;)

So Teflon tape won't help, but a different "washer" might solve your problem.
I use to use for at least five years ELRING #813.052 without any complaints.

View attachment 254286View attachment 254287

When you remove it later it'll be flat like a post stamp - literally. :whistle:




Never please! Unless you love to strip this thread. 😜




Too late. It doesn't even help to express my thoughts.
.
Click to expand...
What is the size on those washers?
 
Upvote 0 Downvote
930.engineering said:
Which exact "aftermarket aluminum oil pan"? American made or far east?
There's some chance the mating surface isn't at an angle of 90 degrees to
the bore and thread. Next, your not so soft Al washer couldn't compensate
for the present deviation.
Click to expand...

That was my first thought. The mating surface isn’t orthogonal to the threads.

BTW - don’t sand/buff/abrade that mounting flange - those microscratches will degrade the sealing of the crush washer by providing a path underneath it.
 
Upvote 0 Downvote
TiGeo said:
Drain plug is M18x1.5. Just whatever aluminum crush washers it came with...normal ones? Haha. They are pretty thin. I just measured one it's 1.3mm thick. I replace it each time.

View attachment 254291
Click to expand...
I wouldn't really call that a crush washer. It's just an aluminum washer.

Crush washers are two planes with an air gap and that gap crushes.

I'd ditch the solid Al washers and try a true crush washer. I get 'em in 18mm from Amazon. I think I use them on some Toyota trans pans and maybe diffs IIRC

An example
https://www.amazon.com/Dsnaduo-Stainless-Differential-12157-10010-M18/dp/B09PBZKGJG/
 
Upvote 1 Downvote
Upvote 0 Downvote
TiGeo said:
I get weeping from the drain plug on my VW MK7 Golf Sportwagen. I have an aftermarket aluminum oil pan that uses an aluminum magnetic drain plug and single use aluminum crush washers. The recommended torque is ~20 ft lbs. Is the weep/leak from:

1) The threads (so you would say use HD teflon tape on them).

2) The mating surface where the crush washer should deform (I think?) to seal the drain plug against the pan.

Do I need to just tighten up (litterally!) and get that crush washer more deformed/tighten it more?

Don't forget folks, this post is set up on the forum using the "question" format so you can vote for the best answer with the arrows off to the right of folks' responses!
Click to expand...
BMW uses copper washers with its aluminum pans.
 
Upvote 0 Downvote
And yeah I know it was already covered but only tapered threads seal, which is why NPT doesn't leak (er leaks less, a thread sealant or tape is still advisable) AND effectively stops at some point without a flange or shoulder. Certainly you can overtighten NPT so it's best to go snug and see what happens.

Also in most cases BPT and NPT are so close you can force 'em together and it works out fine, but isn't technically correct (ARB users know this)

Finally, my experience has been that most pre-threaded NPT available at Home Depot today is horrifically threaded and will leak terribly and fit together poorly. Kinda sad as this is old-school tech.

None of this helps with the drain plug question, either. You're welcome ;)

Sometimes you use (a different) thread sealant on things like valve cover bolts (like '08-11 Focii as an example) but that's more of a splash lube situation
 
Upvote 0 Downvote
TiGeo said:
What parts did you have that you had issues with? I figure an oil pan...how hard can that be haha.
Click to expand...
That was a while ago, but I remember an aluminum thermostat housing that leaked (was supposed to be an upgrade from the BMW composite housing), a fan clutch that failed in about a year (1/2 the price of the BEHR/BMW clutch), a fan housing that didn't fit properly and the last one was a glove box latch that looked identical to the BMW one (and half the price) but when installed it was somehow tweaked just enough that it would not operate properly.

But that was 10 years ago - perhaps it is better now and maybe better for your model. I just learned to avoid Uro and a couple of other brands such as Meyle and Karlyn.
 
  • Like
Reactions: D60
Upvote 0 Downvote
Also I've never really been thrilled with the concept of simple aluminum washers. Al ain't that soft and I think it takes a good bit of torque to "squish" it -- often more torque than I feel most drain plugs should get.

There are a million variables like thread size, materials of the female threads and aluminum washer thickness. And certainly, yes, many OEMs use solid Al washers with success.

Still, I kinda prefer rubber o-rings or rubber washer styles, or true crush washers that should technically be replaced every time.
 
Upvote 0 Downvote
Update. After the track event last weekend I drained the oil and replaced the aluminum magnetic drain plug....I reused the HPL as it has only about 4K mi on it. Steel magnetic plug with copper crush washer...hope this works! The aluminum crush washer that came off didn't look deformed at all. Also the aluminum drain plug 10mm her was pretty boogered from me over-torquing it was 🤣. I'll check it in a few weeks to see if it's leaking.
 
Upvote 0 Downvote
TiGeo said:
No thanks dude. It's good to get under your car once in a while and look around. It's like at most 2x a year. I'll keep doing it old school.
Click to expand...
I use an extractor and swap the filter every other service. Plenty of time to look around. I've serviced a car on Christmas day in my good clothes...

Each to their own, however.
 
Upvote 0 Downvote
You must log in or register to reply here.

Similar threads

C
Stripped transmission drain plug
2 3
Replies
50
Views
7K
The Critic
TiGeo
I've gone full BITOG....I drained oil/re-used it.....
2
Replies
26
Views
3K
TiGeo
paulri
  • Locked
Help me remove a fiber washer stuck to coolant drain plug hole
Replies
10
Views
3K
paulri
C
  • Locked
Leaking transmission drain plug
Replies
19
Views
9K
WyrTwister
M
  • Locked
Sight seepage from drain plug
2 3
Replies
43
Views
4K
atikovi
Back
Top Bottom