I had a used 2010 Prius from…
I had a used 2010 Prius from a dealer with 60,K miles.
I brought it up to 240K miles with a different dealer who replaced everything else associated with it, including timing chain, other gaskets etc.
I'd say the mechanicals were excellent. But they failed to replace a defective horn while it was apart.
The real problem? The dealer system. My first 2010 was only a year old when I bought it, but the dealer hid that it'd been in a major collision -- and sold it as "certified".
It didn't take long to recognize something was wrong, and a technician confirmed it,
but the family-owned dealership denied it. When I tried to appeal, I learned that Toyota Corporate has no control over its dealers. Each dealership is different.
Recently, I traded that 2010 for a nearly identical one with an undisturbed chassis.
I expected it to be as mechnically as reliable as the first because its service record (and CarFax) showed it has always been serviced by a NJ Toyota dealer.
My first Toyota taught me to be suspicious of dealers when a service manager there insisted I needed new rotors & brakes at 100 K. -- I should have laughed at that.
Then they said I had a leaky timing chain cover. Well, I keep my car parked in a garage, where the clean concrete beneath the engine remains pristine. So, forget that one.
The car is better than its dealers. [That dealer system has outlived its usefulness.]
My second 2010 gave lousy gas mileage and began to emit a rattling sound after I bought it, suggesting combustion problems.
Well, 70 years ago, I knew two brothers who'd been WW2 mechanics on the Red Ball Express. Engineers of the time established products like "Rislone" and "Marvel Mystery Oil" to keep the supply trucks running.
I tried the Rislone which cleaned my EGR enough to raise my gas mileage at least 5mpg, enabling me to get 48 mpg on a recent 300 mile drive on the Interstate,
That revealed a cooling problem as the coolant overflows the reservoir. .
I wonder what a coolant flush could do?