Droid13

So, this EV Mode setting had me a bit befuddled. As most people have figured out, it's a bit of a pain to activate, both fiddling with the steering wheel buttons and actually having the request accepted. Also, the speed limitation is quite disappointing (40kph/25mph). My Camry Hybrid did not have an EV mode button, but the hybrid gauge had an "E" position to tell you when you were driving in EV and it was easy enough to figure out how to coax the car to cruise in EV up to 65kph/40mph. The RXh has the "Charge" area on the gauge where the Camry put the "E" on the gauge. There is no way other than driving by the seat of your pants to determine when the RXh is actually driving in "Pure EV" unless you were lucky enough to get the official EV setting to turn on. The Energy Monitor screen and instantaneous FE display on the MFD offer good hints, but not 100% clear indicator the vehicle is running in Pure EV (which I define as engine stopped, as did the "E" position in the Camry) because you can't say for certain if the engine is spinning or not.

So, I dug out my bluetooth OBD module and plugged it into the vehicle so I could monitor some additional engine information on my smartphone, which I setup to display a tachometer and numeric coolant temp gauge (the left side cup holder proved perfect for the purpose). I was going to see exactly when the engine was spinning and when it wasn't. What I discovered is that basically the RX450h works exactly the same as the Camry. You can coax the vehicle to drive in EV up to 65kph. The engine will always spin above this speed. I did some coast tests from 80kph/50mph. The MFD instant FE display and energy monitor might show no fuel or engine use, but the engine is still spinning. As the vehicle slows below the 65kph threshold there will be a momentary bump in fuel usage before the engine stops spinning. This is exactly the same thing the Camry did. It would coast at 0L/100km, then the needle would bump to 2L/100km then settle into "E". I'm not sure if this is done to give the engine a smoother spin down or to have a little fuel hanging around to make for a smoother start.

I read somewhere else on this forum that the first section of the ECO range on the gauge is for EV. I've pretty much confirmed this to myself. I set the h up to cruise in this unofficial EV mode and slowly applied gas pedal pressure. Always at the point the needle reached the halfway line in the ECO zone the tachometer would show the engine spin up. Handy! This is something the Camry did not have, it was always a bit of a guess how much gas you could give it while trying to keep it in EV.

25mph EV? Fuggedeboutit! The RX450h can do EV up to ~40mph like the Prius and Camry. The only thing I can think the EV button selector is for is to try to sneak up on Pedestrians and give them the horn!

Speaking of which, I was cruising in EV and tried to turn EV button on, it said I couldn't, and I said "but you already are!". Ha!

Side note, I was curious about how fast the coolant temp came up from a cold start. Startup at outside temp of -7C (low 20s F?). The dash temp gauge started to leave the bottom at 40C, and crossed the first line at 45C. The temperature rose steadily and linearly until it hit about 70C. I guess this might be the point where thermostats start to trigger. The temperature backed off and bounced around quite a bit here from 60C to 75C depending on if I was stopped at a light, coasting, or accelerating. After about 20 minutes the temp gauge then started a gradual climb to 80-85C where it mostly stayed. I assume that meant everything is up to temp across the board.

RXSF

yes, if you keep the needle in the first half of the green zone, it will stay in EV mode assuming the ICE is fully warmed up. Also if you have the gas engine on, you can dip below "half" of the first green section and it will jump back into EV mode.

vlad_a

The reason the engine starts to spin at higher speeds with no fuel going to it has to do with the nature of the Hybrid system. The gas engine is sandwiched between 2 electric motors, one of which is permanently attached to the wheels. During pure EV operation, the other motor has to spin in the opposite direction to keep the gas engine from turning. However, it is a smaller motor, spinning at a faster speed, so it runs out of its RPM range pretty early. At that point, the gasoline engine has to start spinning to compensate, even though no fuel is sent to it.

Here's a really good animation explaining the PSD functionality (RX is very similar in its principle):
http://eahart.com/prius/psd/

P.S.
I can't sneak-up on pedestrians because the '13 makes a hovercraft noise in the EV mode.