2005 exhaust flange leak / donut gasket

welcome and well done! how many miles on her?

 

all the best with your repair.

 

On some cars those bolts seem too short to thread into the exhaust flange as the spring is pushing against you. What I have done to solve this is to put the spring in a vice and use two plastic tiewraps to capture the spring while compressed so that the total length is shorter. When you get the bolt threaded in or started you can cut off the tiewraps off. Now sometimes part of the plastic may remain but it will all melt off eventually. If it bothers you chisel them off.
Insofar as the metal facing - I would think that the metal faces the flange as it gets hotter than the exhaust pipe lip....then again....hard to say..

 

AS a sidenote its a good idea every few years to tighten up those donut flange bolts as they are spring loaded and tend to loosen up. At the least it will prevent them from becoming welded on.
I checked mine 3 years after I bought the car new and they were really loose.

 

The aftermarket donuts don't seem to fit properly. Dealer one is expensive but fits properly. You could try a salvage yard with Prius. The donuts are usually stuck on the manifold when they pull the engine. Maybe they'll see you one for $5-$10.

As far at fitment orientation it will be obvious when you have it apart. The flat side goes toward the engine, the conical side mates with the exhaust system flange which is conically shaped.

However, I'm afraid to report that you need or will soon need a catalytic converter or there is some other restriction in your exhaust system. The donut should not "wear out". However, if the Cat is plugged and engine under heavy load (going uphill, heard acceleration etc) the exhaust has to go somewhere and the path of least resistance is between the donut/exhaust manifold/exhaust flange.

There is another (smaller) donut between the muffler section and exhaust mid-section. I bet you that one is perfect.

Does your car burn oil between servicing? Do you have poor power going uphill? Has your check engine light "flickered" under load?, Every had a P0420 code? If you answered yes to any of these questions your Cat is probably done. Cars that burn oil definitely clog up the Cat before cars that don't.

When you had the exhaust apart did you look inside the Cat for any "gunk" plugging it up? What about the rest of the exhaust? any part of the pipe "smushed" from off roading etc?

 

My doughnut gasket was making the growling on acceleration noise and throwing the P0420 code. I convinced myself that the CAT had to be replaced even tho an experienced muffler repair mechanic told me that "if the doughnut is gone and introducing O2 into the exhaust stream, that alone will throw the code".

I went to work with CAT, AZ gasket and replacement spring bolts - and a SawZall! Watch out! I heated the nut and thread on the engine side of the flange until I got bored (propane torch) maybe 4 minutes. Then immediately applied bees wax. It smoked a little and the wax was certainly drawn into the rusty thread. I applied twist (14mm with 8" extension, 18" 1/2 drive ratchet wrench. I prayed. I wanted to watch the end of the bolt to see it turn as I applied pressure. If the tip did not turn while the head turned, then I was going to stop everything and take it to the muffler repair guy. It turned, I was kind of surprized, but extremely thankful. While these were loose, I made my cut behind the 1st cat, and it was free. I found that there were 2 tablespoons of light gray powder at the engine side. I tapped it on the garage floor to remove any more loose material. The CAT has 100 or so closed cells mostly toward the bottom, otherwise I can see thru it.

As I start to reassemble it is pretty clear that the AZ doughnut is way to small. I'm pretty bummed because usually the right part is a special order and it is 5 pm Saturday. I turned to Google, not AZ this time and it took me to AZ for part 61106 and 5 others. 61106 has fine print below the description that the ID is 2.40" This is perfect! I slipped it onto the flange tube and it fits perfectly. Very happy.

I will be reusing the original bolts and welding a new CAT back on and watch for codes. It turns out that welding on a Prius is not to be taken for granted. Doing this prep work will take more time than the CAT removal as it is recommended that the ABS computer be disconnected. That means remove the Inverter to get the plug free.