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I'm tracking down what I think is a vacuum leak after replacing my valve cover gaskets and I just noticed that where the EGR valve goes into the plenum I am missing one of the nuts. I think this could probably issues if it's not sealed right? My question is, will any nut do? Or do I need a special nut to seal the hole where the bolt goes through?
The other nut looks like a specialized nut, not just a normal one.
I could welll be wrong, but it looks, LOOKS, I say, like a regular "castellated" nut, I think they're called. I may well be wrong on the name, though.
The little extra part on top is slightly smaller than the rest of the threads, so it clamps the nut tight down onto the bolt, even if the bolt contracts as it cools faster than the nut. Generally, once their put on, then removed, the castellated portion is spread slightly, and so useless. That's why they're "non-reusable" items. Once they've been spread, obviosley, they will become loose, and no longer function as designed. Not a lot loose, but enough.
If it were me, I'd find a place, like McMaster-Carr, that could supply you with all you need for a slightly better price than $3.00 each. I realize they're a somewhat specialized item, but really, three dollars each??
Of course, I'm no mechanic. It may be there's something special about the Toyota nuts, which we all knew already, (sorry, I couldn't resist) so three dollars is a reasonable price.
A "castellated" nut is different; they're used with a cotter pin (like on ball joints). These are lock nuts; they're like "Nylock" nuts, but you can't use a Nylock where there are high temperatures. Like almost all "lock nuts," as 2ToyGuy points out these should not be reused. Or they'll get loose and fall off (ah! that's what happened to 881stgen.)
A little better price here: https://parts.lakelandtoyota.com/pro...rm=90179-08059 But they've got to ship it to you, so even if you had to pay $5 at a brick and mortar dealer, you'd come out ahead. And your time has to be worth something.
We used to refer to them as pinch or squeeze nuts. if you look at the hole in the nut you can see a slight triangulation, as opposed to being perfectly round.
Ok, sounds right.
As a mechanic, I make a darn fine electronics tech, if you see what I mean. I learned a lot from the professional mechanics at my last job, but I remain a professional electronics tech, not a mechanic.
Thanks for the help! I learn something new every day, if I'm not very careful...
Pat☺
03-29-2020, 10:59 AM
(sorry, I couldn't resist) so three dollars is a reasonable price. 
