Torquing Drain Plugs w/Crush Washer

[The Critic]

I did an oil change on my friend's Honda Fit last week. Normally I use a new crush washer and give it a strong tug with my extra-long ratchet, and call it good. I follow this same process (new washer, strong yank with long ratchet) and have never had a leak.

For the sake of precision, I decided to torque the drain plug to 30 ft-lbs this time with my PI torque wrench. Of course, a new crush washer was used.

Here is how it went. I first installed the plug finger tight, then proceeded to tighten the plug with the torque wrench. When the plug started feeling tight, I kept going as the click had not been heard. All of a sudden, I felt the resistance decrease and it felt like the threads were crumbling...for about 1/8 of a turn...at which point I stopped.

Then, I changed my mind and decided to try again. This time, the torque wrench moved the drain plug a hair more, and then clicked. I double-checked with a ratchet and the bolt did not move at all, so everything is probably fine. Upon closer inspection, I noticed that the crush washer is a bit flatter than I am normally used to seeing.

This leads to me to a couple of thoughts:

1) Have I been under tightening these drain plugs all along? I know that the Honda dealer's express maintenance dept requires the use of torque wrenches on the drain plug, and the few times that this car has came back from there, the plug has been on super-duper tight.

2) I have never felt this "thread crumbling" feeling before when tightening drain plugs with new crush washers, but I presume this is what it feels like when the washer "crushes." So, I guess I have never fully, and properly tightened a plug before? But I have never had any leaks.

3) This is fairly new Precision Instruments torque wrench, and the 30 ft-lbs setting is well within its accurate range. I have tested it on other bolts recently and I have found it to be accurate, so I'm sure the torque wrench is not the issue here. Plus, I was turning the torque wrench at a reasonable speed (if not slower) speed.

 

[Shannow]

My Nissan gives two very different feels depending on which way the washer is installed...and I used the second hand ones in the E30 without leaks too.

 

[The Critic]

Originally Posted By: Shannow
My Nissan gives two very different feels depending on which way the washer is installed...and I used the second hand ones in the E30 without leaks too.


Interesting, does your Nissan use the "screw" shaped crush washers?

The pack of generic crush washers (proper size, of course) I have for Honda drain plugs look identical on both sides.

 

[Garak]

Although I haven't messed with many crush washers on oil pans and the like, I've used a lot of them in agricultural applications, and my experience has mirrored yours, Critic, with the resistance decreasing and then increasing again.

 

[eljefino]

I've had spark plugs feel like that. I probably undertorque them. They haven't flown out yet.

 

[JZiggy]

I almost always put a new crush washer on any drain bolt I service. There is usually at least a half-turn of yielding where the bolt is not increasing in tension but the washer simply crushes. These washers are annealed such that they work-harden after install, which is why they should not be reused. But I've heard you can re-anneal them in an open flame (followed with air-cooling) to re-use.

 

[Bluestream]

The crush washer can be used over many times. My 91 BMW still has the original crush washer and has had over 50 oil changes and never a leak. The owners manual says to use a new one each time...

Once you do enough oil changes you won't need the torque wrench any more. You will "feel" the torque in your hand and know when it right.

 

[edwardh1]

whats a crush washer?
toyota sells a metal flat washer that has a "rubber" coating on it, I think its oem, - is that a crush washer?

 

[Smoky14]

You might be under torqueing the bolt but don't forget the drain plug is oily as are the threads thus should be under torqued by some percentage depending on the how slick your oil is.

Long way to say keep doing what you're doing, you haven't lost a drain plug yet.

 

[Trav]

I don't know if they take oil on the threads into account or not but i would reduce torque 15% just to be cautious.
Try 25 ft-lbs next time, it will be fine.

 

[ARCOgraphite]

No torque required on new crush washers if you have a good feel. crush them until resistance goes up then stop. Thats All.

 

[rationull]

I used a torque wrench and Honda's plain looking aluminum crush washers on every oil change in my Civic and my wife's Mazda3 as well as a friend's (all with aluminum oil pans). I usually snug it with a ratchet and then tighten with a beam style torque wrench to ~30 ft-lbs since that's what the manuals call for. TBH I don't remember feeling this kind of thing -- I just remember the bolts getting tighter pretty evenly.

But, I have felt this on spark plugs, and also on my Subaru which has a steel oil pan and uses a steel (pretty sure anyway) crush washer with a "C" shaped cross section. Where the Honda aluminum washers seem to squeeze flat pretty evenly as you crush them, the steel "C" ones seem to have a definitive point where they crush that you can feel. Made me a little nervous the first time I did it.

What do these washers look like?

 

[JOD]

Originally Posted By: Trav
I don't know if they take oil on the threads into account or not but i would reduce torque 15% just to be cautious.
Try 25 ft-lbs next time, it will be fine.


Honda gives its torque spec for dry threads. Ridiculous, but true. If one is using a torque wrench on a Honda drain bolt, your suggestion is a good one.

 

[Quattro Pete]

Originally Posted By: edwardh1
whats a crush washer?

"Crush washers are made of a soft metal such as aluminium or copper and are used to seal fluid or gas connections such as those found in an internal combustion engine."

Crush washers are typically meant for a single use. As you tighten the bolt, a crush washer gets permanently deformed to provide a tighter seal. Next time you take the bolt out, you install a new crush washer.

 

[Boatowner]

I use copper crush washers on both my TDI and Hondas. I tighten with a short rachet until it feels right. I have had a leak nor stripped my threads yet. I replace the crush washer every time. I don't like the aluminum crush washers.

 

[JOD]

Originally Posted By: The Critic


For the sake of precision, I decided to torque the drain plug to 30 ft-lbs this time with my PI torque wrench....So, I guess I have never fully, and properly tightened a plug before? But I have never had any leaks.



You're really not thinking about this in the proper way, and you've misunderstanding the relationship between friction torque and bolt tension.

You've never had a leak and never stripped a train plug. By definition the joint has been tensioned correctly. A friction-based torque wrench may (or may not) help you get the joint tensioned "more precisely". The results are pretty equivocal, depending on a variety of factors. The takeaway however is that fasteners tensioned with a torque wrench still have a ton of variability, sometimes more variability than operator feel. A torque wrench measures the friction to turn, not the tension of the joint. It's simply a proxy for bolt tension (a pretty poor one), not a direct measurement of it. Thing is, a drain plug isn't a tension-critical joint and has a very high tolerance.

This is a long-winded way of saying that the "precision" you're going for with a torque wrench doesn't actually exist. If you're not having a problem with drain plugs leaking or stripping, you've been doing it correctly all along.

 

[Towncivilian]

I replace the copper crush washer on my Pathfinder's oil drain plug every time and torque it to 25 ft/lbs. Same with my mother's '07 Altima.

 

[Trav]

Oh no, here we go with parroting some excerpts from some guys book again!

OP you did the job right, the manufacturer has a spec you followed it using a precision instrument it doesn't get any better than that.

 

[rationull]

Originally Posted By: Trav

OP you did the job right, the manufacturer has a spec you followed it using a precision instrument it doesn't get any better than that.


Although the "dry vs wet" spec is an interesting point here. I've been using a torque wrench on drain plugs to ~30 ft*lbs for years and never thought of reducing the spec due to residual oil on the threads.

Of course, even 30 ft*lbs on oiled threads isn't going to be too tight IMO, but it does call into question the use of a torque wrench when you might be using it to the wrong spec anyway!

 

[JOD]

Originally Posted By: Trav
Oh no, here we go with parroting some excerpts from some guys book again!

OP you did the job right, the manufacturer has a spec you followed it using a precision instrument it doesn't get any better than that.



Besides the ad hominem, can you point to anything I said which isn't correct?

If you want to delude yourself into believing that friction torque is a "precise" way to tighten a fastener, so be it. Some people may be interesting in learning the distinction between "torque" and bolt tension.

BTW, he didn't "do it right" unless he used an OEM crush washer and had the threads of both mating surfaces completely dry.