In this MVS post we discuss the aluminum crush washer.
A Crush washer is maybe the most misused kind of seal in automotive work. They’re commonly found any time a threaded fastener has to seal in a liquid; the most common example is the crush washer under the oil drain plug of most cars. Tighten the plug, the soft copper washer deforms to fill any gaps, making a liquid-tight seal.
What makes a crush washer misused is these are supposed to be one-time-use items. You can maybe get away with reusing them once, if you’re careful; but after that, the washer gets work hardened and doesn’t deform anymore. The usual response to this is to crank down on whatever it’s sealing to try to stop the leak. In the case of the oil drain plug, this usually results in stripping out the threads in the oil pan.
MVS Forum Member MadeInJapan writes:
Was asked by someone on another forum what size aluminum washer he needed for his oil drain plug. He didn’t have one and was going to look for one at AutoZone. Of course the best course of action is to order them when you get your oil filters at some place like fcpgroton.com but if you are ever in this predicament, here’s is the size (I just measured, and it’s easy to remember this!):
1. Diameter is exact size of a quarter (U.S. 25cents).
2. Hole in the middle is exact diameter size of a dime (U.S. 10cents).
(take a quarter & dime with you if you ever have to buy one at a parts store)
This crush washer size evidently applies to all FWD and AWD Volvo’s (not sure about RWD Volvo’s).
Remember that no matter what, NEVER USE A COPPER WASHER. It is too hard and will strip the threads on your aluminum oil pan.
Hope this information helps someone.
MVS Forum Member Tsquared added:
After the second oil change on the 850 I went with a Fumoto brass valve with extended nipple. Happy customer. No problems with oil changes, no more hassel with crush washers, and no need for a oil plug wrench. It does drain at a slower rate so I do have time to pull the filter and perform my other service checks during the standard service. I have over 120K on the valve on the 850, 90K on the valve on the F150, 25K on the ES330, and 80K on the valve on the 944 with no leaks or any issues.