Third time rear coil spring broken

This is rear coils only and not having any trouble with the front struts? It's quite interesting so are you bunny hopping down non-paved roads it pretty good speeds like a lot of my UK buddies would be doing even they so much that I have heard have not had really spring problems on Prius or vibe or matrix so I'm not sure I don't know of any bad runs and springs I used to have my springs wound right down the road from TRD's original shop in California this is way back in the mid '80s I didn't know springs could be this problematic unless they're really being beat on bunny hopping jumping up and down dirt roads with big holes so on and so forth.

 

Anything is possible but my goodness I go over quite a bit of speed bumps and parking lots at speeds not made for the speed bumps right regularly in my old generation too and we go down dirt roads and a long property lines and things like that not at break next speed mind you but dang three coil springs broken I don't think I've broken three in my whole life and I'm old but that is just wild.

 

I've had 2 sets of replacement rear springs over about 10 years. After first set was replaced I was super carful and gentle with them but still they broke and had to be replaced!

 

I've NEVER broken a spring in the 40+ years of driving all kinds of cars. I've had a leaf spring shackle break on me but never a spring itself. I've got a 2002 GMC that had bad ball joints and 250K+ miles, still on original springs.
I believe your real issue is bad aftermarket parts beginning in 2017. I'd look into the price differential between the cheap aftermarket vs OEM part. Oops; 2006 probably difficult to source an OEM part.
Has your mechanic showed you the broken spring or have you actually seen it??? 15K and 2K miles between broken springs??? Something doesn't smell right - too much fish-n-crisp???

 

I've collapsed and broken the coil spring before but not easily. Not one in the Prius and I beat these cars up and down dirt roads pretty badly that's really sunthin. I think these are cold rolled wound coil springs generally pretty cheap like $66 a pop I've had custom winds done many times for older toyoda's lifting purposes and what not . Generally pretty inexpensive endeavor.

 

Is there any markings on an OEM spring to differentiate it from an aftermarket one? If so, maybe pick up a pair from a junkyard and install those?