Heat Retention, Coolant and Thermos

[Tideland Prius]

I was wondering, would the engine cool down faster with the coolant sucked out of it and into the thermos or will it cool down faster with the coolant still in the pipes. I'm guessing without the coolant unless the coolant has a low specific heat.

[rick57]

I believe that the coolant would not cool down any different then any other car. The recovery system thermos only holds approximately 3 liters of coolant. It is tied into the system similiar to having a heater core. Coolant is passed to the engine when the HV system is turned on & the engine is cold. Coolant is circulated into the bottle after the engine has reached operating temp. When full,the ECU will stop recovery. Also when the system is turned off ,when parking for example,and has not finished,it will continue for several seconds till it is finished.

[xevious]

I think what Tideland is getting at is the aluminum engine acts as a heat sink, rapidly cooling the coolant if the thermos wasn't used.

Aluminum has a very low specific heat (about 22% of water) and a very high thermal conductivity. This is why commercial heat sinks are often made of aluminum. I'm not certain what the specific

The engine will cool faster without the coolant, and the coolant will cool faster if left in the engine instead of the thermos.

[rick57]

I think what Tideland is getting at is the aluminum engine acts as a heat sink, rapidly cooling the coolant if the thermos wasn't used.

Aluminum has a very low specific heat (about 22% of water) and a very high thermal conductivity. This is why commercial heat sinks are often made of aluminum. I'm not certain what the specific

The engine will cool faster without the coolant, and the coolant will cool faster if left in the engine instead of the thermos.

Oh I see now ops:

[DanMan32]

I wasn't aware that the coolant is sucked dry from the engine. I thought it was more of a fluid exchange.

[xevious]

Great question. From the Toyota documents I've read, I inferred that the majority of the coolant volume is actually pumped out of the engine and into the thermos. One of the reasons why the engine cannot start immediately upon turning on the car is because the coolant must be pumped out of the thermos.

If my model is correct, however, then the coolant pump is a critical failure point.

Rick, how the heck does this system work???

[jayman]

So the system immediately pumps coolant out of a hot aluminum block motor when it is at full operating temp?

I don't see how. Seems to me you would have a seriously warped block and/or head in short order. The ORNL description and illustrations didn't mention anything about the block being routinely drained.

When you Power On, the electric pump will pump warm coolant out of the thermos into the head to minimize cold start emissions. There is a bit of a delay in doing this before the ICE can start, which seems to depend more on ambient temp and SOC than the thermos.

If it's a nice summer day, no demand for Max Heat or rear defrost, you can Power On, wait for Ready, go into D and slowly drive off in Stealth. At -40, even if the SOC is green, the ICE will almost immediately start.

[prius mdt]

Hey guys - new here, Maybe I can shed a little light.

The thermos and engine are always full. No draining out or moving coolant from one place to another. The hot coolant in the thermos is opened up to the cold engine which does help heat the engine up faster, goes into closed loop faster, reduced emissions, better fuel economy.

The mixing of hot coolant with the cold coolant/engine is not so violent that would cause warping of metal block/head. Instead you get warm coolant in the engine and thermos. The water pump continues to circulate coolant thru the engine and thermos until both are up to temp. After the thermos temp is satisfied, the ECM closes the thermos valve so the water pump only circulates hot coolant thru the engine.

When you shut down, the engine cools off, and the thermos does not.
Rinse, lather, repeat...

[Sufferin' Prius Envy]

The thermos and engine are always full. No draining out or moving coolant from one place to another.

Welcome prius mdt,

Not doubting your post, but do you have any corroborating links, etc. Or are you by chance a Prius Tech?
It’s a persnickety bunch here.

P.S. I hereby donate another point to double your PriusChat Point total to two . Again Welcome!

[rick57]

Ok guys(and any gals following) here goes.
You have an engine,heater core and coolant recovery bottle. There is a 3-way rotary valve connecting all 3. When the engine is cold,Power On but before start, a water pump activates to move hot coolant from the bottle to the engine & engine coolant will refill the space in the bottle.As the engine starts,the valve shuts off the flow during engine warm up and the system has normal operation with coolant circulating thru the heater core. When the engine reaches operating temperature the valve moves again to direct the coolant to both the recovery bottle and the heater core. When the bottle is filled with hot coolant the valve moves again to direct the coolant only thru the heater core,blocking the hot coolant in the bottle.
Any questions? Just ask,maybe I can explain a little better.This is explained in the 2nd gen NCF which has all kinds of interesting info :wink: