Full charge, coast downhill -> engine runs?

There has been a lot of other threads about this. I too have this issue. I work at a college on the side of a 1400 ft hill. Coming down from the driveway onto the main road, the elevation drops to about 1000 almost immediately. I had the same issue with the engine revving up to bleed off the excess energy. I use neutral now. Or during the summer, I crank the air conditioning.

 

Huh??? Your brakes still work perfectly in neutral. No one is suggesting coasting downhill!

 

I think I may have figured this out, although I said that before, so famous last words.

My guess is the engine turns on because something warms up a little too much and it has to circulate some coolant to cool whatever it is off.

I noticed that in the summer time, it'll go on/off pretty fast, presumably because whatever is a little too warm doesn't need that much coolant circulated and the emissions system won't cool off as much so there's no need to re-light the cat. In the winter time, it takes a little longer to turn on because it's not as warm out, but when it does turn on, it runs longer because the emissions system cools off a lot faster.

Having said that, even if my guess is correct, I have no clue what the car's turning the engine on for.

 

Your engine is firing up to help prevent the battery from overcharging while you coast downhill with a full battery, and yes, it is worse in the winter. I even experienced this on level ground while approaching a stoplight and lightly riding the brake for block or so. It's too bad that the engine won't shut down until it reaches normal operating temperature. Coasting downhill in neutral is never a safe idea, but some have tried it to keep the engine off. More opinions in 3, 2, 1....

 

I have experienced the same scenario going downhill on the grapevine ( I5) I get to the full charge and then the engine kicks in. I have learned that as soon as I get downhilli can look at the logs created by the Hybridassistamt app. When looking at the operating temperature it does get too hot because it is producing so much charge through Regen that it circulates coolant to bring that down. I don't like that it won't shut off until it reaches regular operating temperature. To keep it from getting the full charge I usually lightly step on the accelerator while I'm coasting so that I don't engage so much Regen. I usually only press on it lightly enough to make the bar on the HSI to disappear. Hope that helps.

Posted via the PriusChat mobile app.

 

It happens when the battery is far from full. It'll periodically kick the engine on and off as it recharges the battery on the way down.

 

I've actually experienced this going uphill - in EV mode, sticking to around 90 km/h indicated with cruise control, and near the top the ICE kicked in for no obvious reason (did not go into "PWR" section in HSI bar). I must try this again with Hybrid Assistant logging. The hill's about 150m high.