What all goes wrong as a v gets high mileage?

15k on a gen3 engine is hard to believe.

When the oil light comes on you have run out of oil, at least enough the oil pickup is running dry. Just as bad, oil provides cooling for the lower end of the engine in addition to suspending combustion blowby, carbon and dirt. Less oil means it is way hotter and contaminates are higher density.

If you get an engine that literally does not use any observable oil, keep it that way with 5k oil changes like your wallet depends on it. Same basic advice for coolant; every 50k or less, no exceptions.

 

RJ, yours is the question that brought me to the Forum today to post this "Save 9.5K!! As probably many know, the third-generation Toyota Prius models, including the Prius v, are prone to EGR (Exhaust Gas Recirculation) system issues caused by carbon buildup in the EGR valve, cooler, and intake manifold ports. This blockage leads to rough idling, stalling, sluggish acceleration, and poor fuel economy, and if left unaddressed, can result in severe engine damage, including a blown head gasket. Regular cleaning of the EGR valve, cooler, and intake manifold every 50,000 to 100,000 miles is the recommended preventative maintenance to extend the life of the system and prevent costly engine repairs.

My Prius V did not exhibit the idling, stalling, sluggish acceleration right up and until maybe just before the head gasket blew at 135K. Those symptoms were withing 100 miles of the gasket blowing. It did however begin showing decreasing AVG MPG from 60K. We went from 41.1 to 37.8 and it seemed to start after I had the major service at 60K so I stupidly stuck my head in the sand and attributed the decrease to age and the servicing. I never went to the Internet and asked what you've asked here RJ. So, I got what I deserved for acting like an Ostrich.

However had I known that my dealership was going to tell me the cost to replace the head gasket and do the timing chain (a service that makes sense for a 135K Prius when doing the gasket) was going to be 9.5K, even I might have swiveled from work and life's other focus grabbers and asked this question.

So, kudos to you RJ. Check your EGR Valve.

ps. I put your question to AI but it was too general a response. Maybe if you asked it component by component you'd get useful response.

 

Worth noting: this is owner recommendation. From Toyota, crickets.