Toyota Sienna 2016 3.5L V6 Oil Consumption Issue
I kept reading that Toyota engines are barely broken in at 100,000—so when I bought our family a 2016 Toyota Sienna 3.5L V6 with 116K miles, I thought we would be in shape. Unfortunately, it's been burning oil, (white/blue smoke on startup after longer journey's), and our mechanic confirmed it burned 1.25 qts of oil on 750 miles recently.
We have a warranty that has a month to go, but my mechanic says it will be hard to prove what is causing the oil consumption and be prepared for a fight with the warranty company. He did change the PCV valve to see if that is a "quick fix," but we are still seeing (and smelling) white/blue smoke on startup.
What would you be looking for in terms of the issue, and what advice would you give? We don't have the money for a new engine or huge repairs—so I am really hoping to get the warranty company to do their part.
No, sadly not.
Unfortunately that's probably the root of the problem. That Sienna had 116K miles on it when you purchased it, and a lot can happen to a vehicle in that time. When buying a well-used car you can't simply rely on the manufacturer's reputation. Even a Toyota is going to have potentially serious problems if it was not maintained properly or was mistreated during prior ownership.
About all you can do at this point aside from maybe trying the ATS carbon treatment is see if you can get the warranty company to do anything about it. (If they are willing to do anything though they'd probably want to install a junkyard engine, but you won't know until you try.)
Take it as a life lesson - going forward be sure to have a thorough inspection by a good mechanic done on any used vehicle before buying it.
You didn't say what warranty company is involved but most of them are scam artists.
In the event the problem is being caused by carbon buildup and stuck piston rings you could give the ATS Carbon Clean product that Scotty has talked about a try.