Is this unique to the Prius: Coolant "lunch box" and back-up brake power?

1. The engine coolant heat recovery system can be found only on 2G Prius sold in North America. It is supposed to speed up engine warmup time for exhaust emissions reduction. IMO this is an example of unnecessary complexity, except it helped to qualify 2G Prius for AT-PZEV emissions certification in California. The coolant storage tank is in the left fender in front of the tire and can be seen if the fender liner is removed.

2. Prius needs the capacitor bank (located next to the 12V battery) because the braking system has an electrically operated hydraulic pump, called the brake actuator. The brake actuator is needed because the Prius gasoline engine does not run constantly.

Most cars have a traditional hydraulic braking system which receives power assist via engine vacuum (since the gasoline engine is intended to run at all times the car is operating) so #2 is not needed.

 

Keeping the coolant warm for 3 days sounds like a stretch to me. Is that correct? Is that only true with very hot ambient temperature? thank you

 

Yes

 

Yep, only the North American model has the coolant recovery thermos, but they all have the brake capacitor. If you think about it, the Prius had a pretty unique requirement in needing all of it's systems (brakes, power steering etc) to continue to function, even when the engine is off for extended periods of time. This is why the hydraulic system is electrically operated. It doesn't need those capacitor all the time though, even when you're gliding with the engine off it's still really just using the normal 12V power. However they put the capacitors there just as a back up, so that you wouldn't lose brakes if the car suddenly lost its electrical power from the inverter AND the 12V battery turned to crap as well. Most people will never need it, but it's nice to know it's there.

Warm is only a relative term. I assume that they mean warmer than ambient, so probably barely lukewarm after a couple of days. If on the other hand you've had the engine nice and hot and then park in freezing weather for a few hours the thermos is probably very useful for get the engine back to warm more quickly.

 

I've noticed some owners who refuse to replace the 12V battery when it has failed and instead rely upon jumpstarting the Prius for an extended period of time. That is an example of an owner who would benefit from the brake capacitor bank if the inverter pump decides to fail and the DC/DC converter stops operating.

 

Yes I've noticed that too. Lets just say that leaving out the capacitor bank for those people would merely accelerate natural Darwinism.

 

I agree that it is a really bad idea to tolerate a failed 12V battery in the Prius for an indefinite period.

Also agree that $3,500 is high for a 13-year-old Prius with unknown but likely very costly issues. (If it was so simple to repair you would expect the seller would fix the car so it could be sold at a higher price.)

 

No, normal cars use the engine's vacuum to boost the brakes. Since the engine is turning and thus generating a vacuum whenever you're moving, then these should be pretty safe. Even automatics these days can keep the engine rotating without fuel fuel injection when the car is slowing down. The only time it would really let you down is if you were driving a manual and for some silly reason decided to put it in neutral and coast. Then if the engine cut out you would indeed lose brake assist. Of course it goes against all good driving practices to coast a manual in neutral anyway.