We've all been there: you run out of juice just before you reach your destination, causing the ICE to turn on. Question: is it bad for the car to turn it off before the ICE finishes its warmup (thus turning itself off automatically)? I've been in situations where I've sat in a parking lot with the engine running for a full 1-2 minutes before I leave the car because I'm worried that it's potentially harmful to the engine to turn it off before it finishes warming up. Any ICE experts here knowledgable enough to comment on what the best practice is? Sit in parking lot leaving ICE running or just turn it off even though the ICE has only been running for 15-30 seconds and hasn't finished warming up yet?
I don't claim to be an expert but i never turn off my ICE when it is cold. I reason that the gas/air mixture is still very rich and is likely to wash down the sides of the cylinder walls and at least temporarily expose them to metal to metal contact. The warm engine block will evaporate any moisture which may be present as a byproduct of combustion which, if it stays, can form a mild acid with the CO2 and cause unwanted wear. There are other alternatives to sitting in the car while it warms up. It is possible to anticipate running out of electrons and run the ICE first. Then arrive home on EV with a warm ICE. This is what I do as a practice. Sometimes I use the"home" feature of my NAV to estimate the miles remaining to get home and compare that to the remaining EV miles to determine when to switch from HV to EV. That also gives me a reading of the accuracy of my estimated EV miles.
It's especially important to let the ICE warm up in Winter, as if you don't it may develop an ice coating *inside* the engine. When you start it again later on, it will sound as if the engine is destroying itself, as it breaks and vaporizes that ice. Even in Summer if you shut it off too early it will contaminate the oil with things like hydrochloric acid and soot...
Any ICE needs to warm up to a point where it evaporates the moisture that accumulates inside it from condensation. Fortunately the Prius has been designed with this in mind, as it can be a problem with short and intermittent running periods. The coolant system is plumbed to scavenge heat from the exhaust, thereby warming the engine much more quickly than would otherwise be the case. This cuts down on running time, and also helps with the problem of moisture accumulation.
