During our 02's recent incident of no heat, I noticed that the Stage 4 (idle stop/EV) threshold was reached about 2-3 minutes after startup. After coolant was added, going back to normal warmup times (5+ minutes) was frustrating. Would there be some way to reduce engine cooling, get to operating temp ASAP, and then allow coolant flow so I have heat? I'm imagining a solenoid valve hooked up to a button marked "WARMUP ASSIST" or "WARMUP." I was also thinking about a secondary air induction hose running near the hot exhaust manifold, with an electric valve hooked to a similar "WARMUP ASSIST" switch. That would allow fast warmup to idle-stop mode in the winter, and maximum power and efficiency (using the stock cold air intake system) once warmed up. Has anyone tried either of those ideas? I know warm-air intakes are quite common in the Insight community.
There already is a device in the coolant path called a thermostat. It operates automatically. Exhaust heat recovery existed for a long time on a LOT of engines but I think they were eliminated when their usefulness was found to be tiny compared to the cost of maintenance.
From a bit of internet research, Exhaust Heat Recovery systems are used on some newer Prius models, but not gen1. https://www.energy.gov/sites/default/files/2014/03/f8/deer11_barrieu.pdf
