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Today at Atelier Kaz - Private NSX Enthusiast, ex-Honda R&D engineer with F1, Indy/CART background

OEM Header Tank 03

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This is the water passage of our engine.


The hot coolant is cooled down at the radiator and then it is returned to the WP through the centre pipe running inside the V-bank under the intake manifold as indicated in light blue arrow (should have used blue arrow instead because it's the same flow as the coolant returning from the radiator via thermostat after being cooled down.
It's not the same flow as the one returned from the Heater core indicated in the light blue arrow....
.).

Then the WP pushes the cooled coolant from the radiator towards the front and rear bank cyl block.


This will absorb the heat energy from the engine into the coolant while passing through the block and part of the head then the hot coolant from both banks enter the water passage as indicated by the red arrows.

Two flows are merged into one and if the thermostat is open, the hot coolant is sent to the radiator in order to cool it down.

The same flow is used for the heater control.

If the water valve is open but the thermostat is still closed, the hot coolant still travels through the same pipe but won't pass through the radiator and instead, it will travel upwards at the T junction before the radiator and heats up the heater core based on how far the water valve is opened.

If the thermostat (and the water valve) are closed, the coolant simply circulates within the engine to speed up the warm up sequence.


Here comes the nice design.
After the hot coolant from the front and rear bank are merged, in order to filter out the air, there is a chamber built into the water passage body forcing the upper stream of the hot coolant to be passed through the expansion tank as marked in pink arrow.
The air is most likely to be at the upper stream of the hot coolant so this chamber design will efficiently capture the air and transfer it towards the tank.

As soon as you start the engine, the WP starts spinning and thus, this flow towards the expansion tank begins immediately and it will continue to do so until you stop the engine.




If you have OEM tank, you can see the continuous coolant flow from the small hose connected at the upper side of the tank close to the tank cap.
If you adjust your viewing angle, you should be able to see the fast stream of coolant shooting horizontally just below the brass tank neck in the direction towards the front of the car.

Not easy to see in this video but you may be able to see just about a few mm width white stream of coolant below the brass filler neck.


Considering the surface tension of the thousands of tiny bubbles and in order to filter out the air thoroughly from the coolant, it requires enough length of filter passage.
At the same time, the tank needs to be able to hold enough level of coolant as well as enough open space to cope with the increase of volume when the system gets hot.
Within the limited space in the engine bay, Honda decided the size of the tank and designed it with multiple chambers connected with the tunnel (hole) each others inside the tank.


One side of the tank surface is about 25cm x 20cm.
With the tank cap pressure setting of 1.1kgf/cm2, it will be more than 500Kg applied to that single surface/side with thermal shock, vibration and pressure cycling when the engine is started/stopped.
In order to cope against this huge force with the use of plastic resin under severe conditions while filtering out the air from the coolant, each chambers walls were designed in round shape with small capacity.
If similar shape tank was made out of the metal sheet, it will need consideration on the thickness and welding point/spec against this huge force under the above severe conditions so personally, just pressure testing is not enough.


As mentioned earlier, you need to consider the friction/drag of the coolant from the WP point of view for the cooling efficiency as well as for the prevention of cavitation.
If you are thinking of using aftermarket parts such as multi flow/return radiator, you must use the one designed and tested with the above point in mind especially if you are tracking your NSX. Any friction will reduce the flow rate and will increase the chance of cavitation. Some of the aftermarket tripple flow radiators were tested on track using real NSX for more than 12months before they were made available on the market.


It is important to replace the coolant at least at the specified interval.
If we ignore the corrosion, plain water is much better than the 50% pre-mixed coolant from the point of cooling efficiency.
If you track your NSX regularly and live in the area where it won't get super freezing cold, you can dilute the mixture to 30% and replace the coolant every 2 years instead of 5 years for the Type 2 coolant. That's what many NSX owners do in Japan if tracking their NSX.







If you didn't replace the coolant for many years like on low annual mileage NSX kept inside museum condition, you may end up with this situation.

The coolant acts as anti-corrosion as well as anti-cavitation. Over the years, the corrosion inhibitor and the chemical (silicone like) for reducing the cavitation will loose their strength.
Eventually, the rust will build up at WP and coolant pipe fitting area.

This NSX looked like never driven under the wet condition so the suspension area, engine bay, the area under the engine, etc looked so clean with almost no rust.
However, once you start opening the engine, you will notice the true story of low annual mileage car.

As mentioned many times in my blog, moisture can enter the engine through the valve left open after you stop the engine and with the air temperature change, it could cause condensation inside the engine. If the car was not used regularly, this moisture will eventually overcome the thickness of the oil film next time when the engine was started. The camshaft lobes showed deeper scratch markings due to build up of moisture from condensation, cooling system was heavily corroded and I actually managed to push my finger through one of the pipe at the water passage.

The rust eventually modified the shape of the WP impeller surface and I think it caused small cavitation and grabbed off some of the metal material that is very unusual for our NSX.
Not easy to see in this photo but one of the impeller surface at the back showed lots of tiny dent as if the ice cream scooped out by multiple tiny spoons.

Another reason why I recommend the owner to replace WP regardless of the mileage as you won't be able to check this without removing it.




Rust and smashed metal travelled everywhere inside the cooling system so took ages to flush out the debris.


Another reason why I recommend driving it regularly and not just keeping it as a garage queen.

Updated 24-11-2014 at 04:11 PM by Kaz-kzukNA1 (extra info)

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Cooling

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