Accidently broke off a nut thread

Initial thought, and considering the type head it has, I'd be willing to bet the stud is threaded into the base metal. Use a good tool, like quality vise grips, to grasp the remaining stud and see if it will unthread. If you have a small pencil type torch, you can use it to heat the stud. It most likely has loc-tite or something similar. Heat it, let it cool, heat it again. Do it a few times and it should release the loc-tite to make it easier to get out, just be careful of other 'car pieces' nearby. May even want to put some type of barrier to prevent accidently getting anything else too hot. After a few cycles, try to loosen it. May want to research to determine if it's standard or reverse thread. Previous experience on other brands has shown to be standard threads, but I've never had the opportunity to do this on a Toyota. Did it snap while tightening it, or loosening it? If worse comes to worse, pull the manifold and take to a machine shop, but if it comes to that, may be cheaper to just get a replacement at a salvage yard.

This may be a bit more reliable than vice-grips if you want to purchase a new toy or have a local place that does tool rentals.
Now I just have to figure out how to get this dang BING crap to stop taking over my browser. I think I'd choke the life out of whoever makes it do this.

stud removal tool - Bing video

I looked through my copy of the repair manual and searched online, but I can't find the Toyota part number for a replacement stud. I'm pretty sure they're available, but it may be one of those things a dealer has to look up. Or you snatch one out of a salvage yard.

 

No need for Vise Grips. Get another M8x1.25 nut and tighten them together with two wrenches. Then, turn the bottom nut anti-clockwise to remove the stud. This is the standard procedure with studs that do not have a drive head.

 

The new stud requires to be tighten into the hole with an 8mm external Torx socket.

 

Ah, you're not the first on PriusChat to have done that. It deserves some boldface, in the hope of catching the eye of some later reader who might make the same mistake:

Look twice (or more) at torque specifications to notice whether they are given in inch-pounds or foot-pounds! Fasteners will not survive if you try to tighten them to twelve times the spec!

After you've done this a while, you get a good sense to look at the thickness of a bolt and say "no way is foot-pounds right for that." But learning by busting stuff is frustrating.

You might have some extra trouble getting the stud removed, as it is now tightened into the timing cover not just to its original intended torque, but to as-high-as-you-ended-up-getting-it-before-it-snapped. You should still get it out eventually, but it might be extra stubborn.

 

at least it snapped at the threads. The body of the stud should be significantly stronger. That gives you a fighting chance of getting it out.

 

It has 3 threads showing.

 

The stud has Toyota part number 90126-06019 (list price $1.93), and the nut, 90179-06299. See catalog Figure 16-03, Radiator & Water Outlet; click View More Images, and then select the second image.

 

It's weird, because that's what I originally found also, but when I tried to verify it on dealership websites, it kept coming up as not being for a Gen 2 Prius, but for a Camry. Maybe that's just a glitch in their inventory system.

 

or maybe it's a me glitch, because when I put that into the same website now, it shows as a fit. I could swear I tried it/verified the part number several times, but probably operator error.

good call @Elektroingenieur

 

With just 3 threads showing, might not be able to do the double nut trick. Screw one nut on, then weld the middle, good as possible.

 

Everyone who mis-reads inch pounds as foot pounds is probably beating up on themselves enough already, but anyway:

The difference is twelve-fold, ie: 96 inch pounds is 8 foot pounds. This is an example where you have to keep common sense in play.

The other case I recall was the bitty hold-down bolt on the spark plug coil. Snapped it right off, in the valve cover.

If you've got a little toy-sized bolt, and the Repair Manual is telling you to get out the big-boy torque wrench and dial in 80~90 foot pounds, more than the wheel lug nut torque, stop and think a sec.

For small, secondary bolts, just one-handing it with a ratchet wrench is often the safest approach. With a water pump yeah use the torque spec, but read it carefully. Throttle body is similar I think, has 2 bolts and two studs-with-nuts, 7 foot pounds IIRC. And the studs are something like 48 inch pounds (4 foot pounds).

 

On small bolts or fasteners that are 6 or 8 mm with 10-13 mm hex heads, I almost never use a torque wrench. I use a small ratchet and drive the fastener down to contact.

Then, I turn it to no more than a 180 degree turn, which almost always results in the correct torque.

Experienced technicians almost never use a torque wrench except for critical engine components like bearing caps and head bolts.

 

I've had one of these in an Amazon Shopping Cart for a coon's age, a little reluctant due to the price up here. But something like this can keep you out of trouble with small bolts. Good for stuff like the bolts on the engine underpanel:



It'd be nice if they had a stubby version too, the above won't fit in some applications.

 

On the alternative, much cheaper would be a widely available 1/4 inch square drive handle that you could epoxy to a 1/4 to 3/8 adapter.

 

Regarding the OP's dilemna, I was watching a South Main Auto video, and he mentioned a special socket that's one-size-fits-all for gripping seized studs like this. It has internal cams that grip/bite when you turn it. Can be used for tightening or loosening. Anyone know the name of that?

Twist socket?

Here's that video, at the point he shows that stud-extractor socket:

PSA: this guy's in up state New York, so maybe disinfect your monitor after watching.

 

DIY "torque limiter", also handy for installing bolts in tight quarters:

 

My 1/4 inch square drive micro-ratchet:

 

I don't get it, how does it works?