Just bought RX450h (2012).... when I start the car it immediately starts the petrol engine and I thought it was supposed to be silent initially.....what am I doing wrong ?

 

Usually there is a several second delay before the engine starts, but not always. Immediate engine starts are not frequent, but not necessarily abnormal either (in the absence of any warning lights). Temperature, battery charge, HVAC settings may play a role. If you want to test the possibilities, try starting the vehicle when the engine is warm and the HVAC settings off. In these conditions unless you're touring Antarctica the engine should wait a few seconds to start.

 

When stone cold, after the green READY light comes on, the engine will start after a few seconds, to heat up the engine. If it doesn't do that, your heater won't get any warmth, as it gets its heat from the coolant.

I found on mine that if I turn off the HVAC, the engine stays off for longer as there is no need to supply any warmth to the heater (as the driver is switched it off).

Also, I believe the hybrid is not driven by the engine through the gearbox for reversing - I think that reversing is a 100% electric affair on the 450h. So the engine will need to kick in to supply additional power if the hybrid traction battery is getting a bit low or simply more electric power is required for reversing than can be provided by the traction battery alone.

 

OP, you do nothing wrong.
As Droid said - mostly it goes down to two variables:
1. battery state of charge at the time you start the system. If traction battery is fully charged (well, at 80%) vehicle should roll back without ICE starting. Done this many times on two hybrids. So you sort of need to see, what exactly is your battery gauge showing charge level wise. Try parking with battery fully charged. Damn it, bars being light blue, it'll qualify as fully charged, and see what happens. As real life example, I could get my Camry hybrid quite far away from parking without ICE starting. RX or Highlander goes in reverse just fine without any additional power request from ICE.
2. outside temperature. ICE starts not to provide heat to the car. It starts to warm up catalytic converter and other emissions related components. Hence, in cold temperatures (anything below 50 and counting) it will start rather quickly or immediately, if it's very cold.
That said, if it's nice pleasant 75 degree Florida morning and battery is showing almost full battery charge - ICE should not start right away. If it does - you have traction battery issue.

 

Without any warning lights, I would say this a possible situation, not an absolute.

 

That's not entirely true for the RX450h - unlike the RX350 which has a cataytic converter which needs to get up to full temp, this is not the case for the 450h. If the HVAC is off, the engine doesn't bother to keep running once coolant temperatures have warmed up slightly. It's easy to test this out - turn on the heater with the coolant temperature at 50 deg C and the engine starts. Turn off the heater and the engine stops. There is a coolant circuit in the 450h exhaust system to capture some heat from the combustion process - to warm up the coolant as the engine doesn't stay running all the time. There is no such heat exchange system in the RX350.

 

I have seen references that say the transitions mentioned below depend on coolant temperature. I have also seen references to the importance that HSD gives to keeping the catalytic converter warm, to reduce emissions. I will simply refer to the system temperature in the discussion that follows.

The Stages:

S1:

In Stage 1 the ICE is cold. If not prevented by use of the EV switch, the ICE will start a few seconds after the car is powered On. Until the system reaches the S1/S2 transition temperature, the ICE will run continuously. This accounts for the anomalous observation of electric regeneration or no arrows (coasting) at the same time as a low instantaneous mpg reading. No power is being drawn from the ICE, but it is running. Also in Stage 1 you will notice that battery power is used for even mild acceleration. In Stage 1 the HSD prefers not to draw power from the ICE if it is not necessary. You cannot enter EV mode while in Stage 1.

S2:

When the system temperature reaches 40 degrees C. (104 F.) the computer goes to Stage 2 operation. The original Japanese poster gave more detail than I clearly remember, but it appears that in Stage 2 the ICE will shut off if it is not needed to provide power. At a stoplight, in S2, the ICE will stop immediately and fairly smoothly. However, the car will not go into golf-cart mode in Stage 2. It can draw power from the battery or it can recharge the battery, but will not use the battery without the ICE. I have not ascertained if you can enter EV mode from S2.




That was quote. I have TCH detailed manual at home, with stages description and PRIMARY ICE start up at Stage 1 is referenced to cat warm up and emissions components warm up. After all, TCH was a PZEV, what comes with priamry concern on emissions, not on passenger comfort.

 

I can confirm some of the information above matches my observations.

When the Power Button is pressed ON and the Ready green light comes on from stone cold, the engine starts about 10 seconds later, even with the traction battery full. The engine will idle or be running continuously, regardless of transmission gear position. I observe from the coolant temperature readout on my Scangauge II that the engine only stops running continuously at 40 deg C (104 deg F). After this point, the engine will stop running, if not required to drive the vehicle.

I've also observed that if the airconditioning system is ON, and in heat mode, the engine will remain running until coolant temperature reaches in excess of 65 deg C - at this point, there are several further observations:
1. the temperature gauge on the instrument cluster is now pointing at the fourth mark
2. the temperature gauge never moves any further up even if coolant temperatures range from 65 deg to 85 deg C (full operating temperature) - this is rather misleading because it does not move up and down relative to true engine temperature
3. the ICE stops continuing to heat up the coolant at the 65 deg C point because there is now appreciable heat for the HVAC system to warm the cabin.
4. if the HVAC is in the OFF position, the ICE does not bother to keep running from the 40 deg C coolant temperature point if vehicle is stationary.

The last point is the bit that I am saying - at 40 deg C - which is only slightly warmer than body temperature, the ICE stops running if no heat is required of the HVAC system and the vehicle is stationary. But if heat is required, and the vehicle is stationary, the engine keeps running till coolant temperature gets to 65 deg C. Normal operating temperature when driving at constant highway speeds is around 83 deg C.

So if stationary in traffic conditions, it is possible to save a small amount of gas during the warm up phase of the engine from stone cold by simply switching off the HVAC/heater.