Engine starts when car switched on - why?

Your owner's manual actually explains this.

It *must* get the engine to a certain operating temperature in order to reduce emissions.

What does the owner's manual of your shiny new $25,000 toy say?

Thanks for your predictable and oh-so-helpful response.

Need help or instructions on how to open the glove box?

No I'm OK with that, thanks. I will know better in the future, though, than to come here looking for info about Priuses (substitute your own more-correct-than-mine version of the plural here.)

Marais

We've noticed that you still haven't bothered to read the owner's manual to your shiny new $25,000 toy.

Why is that?

Are you demanding that the world spoon-feed you basic information that's included as part of your $25,000 purchase? You shouldn't HAVE to read the manual, is that right? After all, you know how to drive, right?

This is a great resource for information about Priuses.

It's just not the place to come to have people read the owner's manual to you, that's all.

Now, if you HAVE read the owner's manual and you're confused about something or you've found it has omitted something crucial, that's fine.

But don't sit on your fat ass, too lazy to reach for the owner's manual, and ask that it be spoon-fed to you by others in the world.

Hey, I've got an idea: why don't I answer your question, in return for you painting my house?

Shagnasty , moms still not putting out or you just having a bad day?

Just keeping the noise out.

All cars have coolant overflow tanks , its not for storing heat its coolant overflow

nonononono, he's right. The 04-09 Prius models use a vacuum flask into which the coolant is pumped AFTER the car is turned off. The goal is to store heat that is pumped back INTO the system the next time the car is turned on. This helps the car heat more quickly, which helps with emissions.

In fact, after an overnight sit one can hear the coolant pump back out of this vacuum bottle after one opens the car door. This is in anticipation of the car being turned on to drive.

I will say that this seems to be a lot of complication--and cost--for very little effect.

It's a Prius, eh?

Toyota was trying to achieve something, and the devil is in the details.

Taken as a SYSTEM, the Toyota Hybrid Synergy Drive is a rolling work of art--and the SYSTEM includes the vacuum bottle.

But by itself, would adding the vacuum bottle to a normal car do anything for it? Sure, it would do the same thing--that is, present warm coolant to the engine so that the engine heats up faster to help lower emissions. But if the rest of the car isn't particularly tuned for that task, the vacuum bottle would e a lot of complication and cost for very little effect.

IIRC the flask was required for the USA spec PZEV emissions rating, along with the bladder in the fuel tank. Other countries got neither device but some did get rear disk brakes.

The NHW11 had an HCAC system (hydrocarbon absorptive catalyst), the NHW20 has the flask, and the ZVW30 has exhaust heat recovery. All 3 systems lessen the unburnt fuel emitted on a cold start.