[CapoTexas]

Ok, so being a nerd I felt like I had to figure out the liquid cooling system(s) in this car. Turns out there are three. The engine block is cooled like any other gas engine by antifreeze, a big radiator, and an electric pump (unlike the belt driven ones in other cars).

The electronics handling the high voltage switching and DC-DC conversion (the rectangular metal box called PCU) has a completely separate antifreeze-cooled circuit with its own smaller electric pump and its own radiator and tiny reservoir. The PCU radiator is at the very bottom of the bumper and is only a few inches tall. The electric pump for it is driver side about a foot or two down. The reservoir is the little pint-size thing to right of the main radiator (not connected).

The transmission fluid is cooled by a third radiator located underneath and behind the driver side fog lights in the bumper. You can see it through the holes there. Again, this one too is completely separate from the engine radiator.

In case anyone cares about such trivia...

 

[beww]

Ok, so being a nerd I felt like I had to figure out the liquid cooling system(s) in this car. Turns out there are three. The engine block is cooled like any other gas engine by antifreeze, a big radiator, and an electric pump (unlike the belt driven ones in other cars).

The electronics handling the high voltage switching and DC-DC conversion (the rectangular metal box called PCU) has a completely separate antifreeze-cooled circuit with its own smaller electric pump and its own radiator and tiny reservoir. The PCU radiator is at the very bottom of the bumper and is only a few inches tall. The electric pump for it is driver side about a foot or two down. The reservoir is the little pint-size thing to right of the main radiator (not connected).

The transmission fluid is cooled by a third radiator located underneath and behind the driver side fog lights in the bumper. You can see it through the holes there. Again, this one too is completely separate from the engine radiator.

In case anyone cares about such trivia...

And of course, another separate cooling system for the HV battery.
The car is a rolling collection of computers and cooling systems.
But I love it.

 

[Carbuff2]

Is there a change interval for ALL those systems? Does the PCU system use Honda Type II blue coolant or something special?

 

[CapoTexas]

Is there a change interval for ALL those systems? Does the PCU system use Honda Type II blue coolant or something special?

I have no idea if there’s a specific change interval called out in the MM. Maybe it’s lifetime coolant since it is NOT subject to engine combustion products and oil and stuff. It is a blue fluid. If you have this car, just look at the pint size white tank to right of radiator (the larger one to the left is engine coolant). You will see it is blue in there.

 

[pick1e]

I noticed the manual says "Do not attempt to check or change the transmission fluid yourself." There appears to be a dipstick with no clear marking, just a little dark red paint. I wonder why that is. Hopefully by the time the warranty period expires we will have much more information on it...

 

[pick1e]

Maybe it’s lifetime coolant since it is NOT subject to engine combustion products and oil and stuff.

The engine coolant is a closed system and should never be exposed to those things either. It just breaks down over time. I bet the PCU coolant should be changed at the same time as the engine coolant.

 

[beww]

The engine coolant is a closed system and should never be exposed to those things either. It just breaks down over time. I bet the PCU coolant should be changed at the same time as the engine coolant.

I'm not sure what temperature the PCU coolant runs at. If its significantly cooler then the engine the coolant it might last longer.

 

[williamsji]

The electronics handling the high voltage switching and DC-DC conversion (the rectangular metal box called PCU) has a completely separate antifreeze-cooled circuit with its own smaller electric pump and its own radiator and tiny reservoir. The PCU radiator is at the very bottom of the bumper and is only a few inches tall. The electric pump for it is driver side about a foot or two down. The reservoir is the little pint-size thing to right of the main radiator (not connected).

Thanks for this part here.

We were discussing the PCU a couple weeks ago and I speculated it was on it's own separate cooling circuit, but not owning one, I could not personally search for it to confirm.

Mystery solved.

 

[Carbuff2]

Is there a list in the Maintenance Minder section of the Hybrid Owner's Manual that says what services the MM codes require? That could answer the question...

 

[pick1e]

No it does not have an entry. What I was getting at but didn't state directly is I wonder if a dealer changes the engine coolant, possibly they are instructed to change the PCU coolant at the same time.

 

[williamsji]

No it does not have an entry. What I was getting at but didn't state directly is I wonder if a dealer changes the engine coolant, possibly they are instructed to change the PCU coolant at the same time.

It's quite possible that the fluid used in the PCU cooling circuit is NOT coolant. It could be a light oil or even AC style coolant, and may never require service during the normal life of the vehicle.

Could be something similar to what is used in small power transformers, or even what is use for liquid cooling systems in modern personal computers. These normally never require service unless/until there is a leak.

Clearly the goal is to use a closed loop corrosion free cooling circuit for a device that creates thermal heat as part of the power semiconductors contained within.

 

[beww]

It's quite possible that the fluid used in the PCU cooling circuit is NOT coolant. It could be a light oil or even AC style coolant, and may never require service during the normal life of the vehicle.

Could be something similar to what is used in small power transformers, or even what is use for liquid cooling systems in modern personal computers. These normally never require service unless/until there is a leak.

Clearly the goal is to use a closed loop corrosion free cooling circuit for a device that creates thermal heat as part of the power semiconductors contained within.

I'd think they would want to use a coolant that could not, under any circumstances, conduct electricity.
They probably wouldn't want to use any water-based coolant for that reason. Oil based is more likely.
I haven't seen the inside of the PCU, but I have seen the Toyota equivalent. The coolant is in direct contact with the transistors (MOSFETS in Hondas, IGBTs in the Toyotas).
I have worked on transmitters that used distilled water as a coolant. It doesn't conduct at first, but after a few days it picks up enough contaminants to start conducting. We measured the current through the coolant, usually in microamperes, but at 10,000 volts even that little can be an issue.
No hybrid uses anything close to that voltage, but the issue still exists.
The best coolant for the purpose would probably be PCBs, but the EPA would probably have something to say about that. Mineral oil would work almost as well.

 

[Carbuff2]

Come on, @beww . Look in the BIG owners manual and tell me what it says about changing that fluid..

I can't believe it would be blue if it wasn't Honda Type II. <--- I'm a poet, that rhymes!

 

[beww]

Come on, @beww . Look in the BIG owners manual and tell me what it says about changing that fluid..

I can't believe it would be blue if it wasn't Honda Type II. <--- I'm a poet, that rhymes!

I'd be careful analyzing chemicals by color. Sulphuric acid looks a lot like water.
If you want more poetry:
Willy was a scientist, Willy is no more, for what he thought was H2O was H2SO4.
If it is engine coolant they must have an insulated path for it, you wouldn't want it in contact with a few hundred volts.

 

[600JSC]

Could the radiator for the transmission used to primarily cool the two integrated motors?

 

[AML61]

In the user manual it is specified that the engine cooler is honda type 2 and the cooler for the inverter is still honda type 2.

 

[CapoTexas]

Could the radiator for the transmission used to primarily cool the two integrated motors?

yes - I heard it was for that on the Weber Auto YouTube channel on a recent vid. There’s no torque converter on these cars so there’s no heat generated from turbulence. Just the electric motors

 

[Carbuff2]

In the user manual it is specified that the engine cooler is honda type 2 and the cooler for the inverter is still honda type 2.

Thank You,


That is a start.

I'm still waiting to hear if the Replace Coolant code in the MM indicates whether to replace BOTH or just engine???

 

[michaelj3]

Anybody own the SERVICE manual for this vehicle, it surely will tell what is needed...

 

[pick1e]

I am still waiting on the owner's manual I ordered a month ago. I only have the "owner's manual lite" that came with the vehicle. I don't know how expanded the supposed full manual is.