As I didn’t want disturbing your nice build thread, thought about not posting here.
However, you are happy for me to do so and other owners may re-visit your detailed thread in the future, going to add my experience here.
I wrote this for other owners when asked about how I bleed the cooling system years ago and it’s cut and paste of multiple messages from the past.
Very old info but should be still useful.
First, the basic.
The method in Workshop manual is OK but mainly written based on the theory.
The entire coolant capacity including the tank is about 16.5L for the C30A and about 16.2L for C32B.
If using aftermarket radiator, you'll need extra amount depending on the spec.
Because the hose/pipe goes up and down across the entire cooling system, you can't drain all of the coolant even if you replace the radiator, hose and the thermostat.
You will be able to drain only about 12 - 14L of coolant depending on what was removed/replaced and also the procedure taken.
With the air bleeding method in the workshop manual, if you study each components including the water passage, coolant flow, heater core, etc., you will understand that it will leave several air pockets within the system unless you use dual stage vacuum pull/fill method.
At the factory, there is a big machine creating deep vacuum and that's how the cooling and the brake system are filled.
Obviously, it starts with an empty system so much easier than already partially filled system.
When you remove the cyl head, you will notice that fair amount of coolant left inside the water jacket/block due to tilted eng installation and the position of one of the eng block drain port.
Even after opening all of the drain ports, if you have experience of replacing all the coolant hoses, you would know that quite a lot of coolant was left inside the system.
If using single stage venturi vacuum pump like the one in your photo, the performance is very basic and heavily depends on the temperature, amount of coolant left in the system, the compressor performance, etc.
I used to use one and I never managed to exceed more than 70% vacuum with my setup.
In fact on the first usage, I measured the amount of coolant filled and straight away, I noticed huge amount of air left in the system.
If you squash the big coolant hose attached to the thermostat cover many times, you may be able to feel and hear the bubbles created or if no coolant in there, you may feel/hear nothing.
That’s how much air could be left using the single stage basic vacuum pump on NSX.
It works nicely for the ordinary production cars with the short cooling system length and much smaller coolant capacity but not enough for our NSX.
NSX has really long cooling system length and as mentioned above, more than 16L of coolant for NA 3.0/3.2L engine.
For the clarification, it will work if other conditions were met but haven’t seen one at reasonable price tag.
Similar to what you can get for the HVAC vacuum pump between the single, dual and triple stage models.
I also use dual stage pump for the A/C Refresh as it's so much quieter and easier to get rid of any moisture left.
I kept using the single stage basic tool for a long time because I use different bleeding method from the workshop manual any way so the vacuum fill was more of keeping the area dry and clean.
Not for getting rid of the air pockets.
Later, I switched to the dual stage type and it significantly improved the air pocket situation.
As you can see, always managed to pull deep vacuum and although I still carry out the same bleeding method described below, most likely, no longer required.
By the way, it’s always good idea to measure the amount of coolant filled into the system.
You won’t know how much fluid left in the system so there is no single figure for all cases but if you repeat the same procedure many times, you would get some idea on the expected amount of new coolant to be filled. If big difference, something is not right.
Any air left inside the heater core could take ages to be pushed out from there so make sure to bleed thoroughly.
When the eng is cold, the thermostat is fully closed so the coolant only flows through the eng block and the heater circuit.
There is almost no coolant flow through the radiator back to the engine at this stage.
Therefore, any air pockets trapped in this circuit won't move until the thermostat starts opening.
There is a tiny float/jiggle pin on the thermostat that helps the air bleeding process.
Above should be enough as the starter.....
Now the actual bleeding procedure.
Not a must but if you can get hold of the coolant refill funnel that you can attach at the coolant tank filler neck, it will save your time.
Basically, the gravity speeds up the process.
Depending on the model, it will help removing the eng bay cover.
I normally remove it when working around the engine any way.
No need to lift the rear of the car.
Keep the coolant tank cap removed throughout the following process.
Keep water valve fully opened.
Turn IGSW into P2 ON, set CCU at max temperature setting and wait for about 30sec.
No need to actually turn the fan/blower On.
Just keep the CCU Off and turn the temperature dial fully clockwise.
This will move the water valve lever fully open.
Turn IGSW back to P0 OFF after waiting for about 30sec.
Or, if you have disconnected the A/C CCU and can't operate the water valve, just remove the control wire and manually open it.
If you look at the valve lever, there is even an arrow with engraved text 'SHUT'.
Move it in the opposite direction, obviously.
For the LHD, the lever should be pulled towards the radiator.
For the RHD, it's towards the cabin.
After filling the coolant using the vacuum fill or whatever the method you used and before bleeding, if it’s safe to do so, start the engine for about 30 - 60sec and stop.
This will push some of the air pockets in the heater system towards the heater core or back to the water passage.
Now top up the coolant tank up to the filler neck.
Yes, you read it right.
Fill it to the neck.
This is why I use the funnel at the tank because later, you need to top it up to the neck multiple times.
With the funnel, you can speed up the process by adding extra coolant above the tank.
Attach clear tube (about 2m length) to the 1st bleeder plug (thermostat cover) with the other end in empty container that can hold at least 2L.
You are going to rely on the syphon effect so keep the container as low as possible.
Open the bleeder and keep it open until you collect at least 1.0L of coolant in the container.
Ideally 1.5L.
Hence, you must fill the tank to the neck or above using the funnel.
During this process, keep coolant level above the MIN line of the tank.
You can go well below the MIN line before allowing the air being sucked back into the cooling system but you want big enough safety margin.
You don’t want repeating the same process again.
The MIN line is just above the air separator of the water passage and while the air can enter from the top small coolant hose, any air left in the separator chamber would be easily pushed out towards the tank once the engine started but you want to prevent the air being introduced during this process.
Close the bleeder plug, top up the tank to the filler neck or add enough coolant in the funnel.
Move on to the radiator bleeder plug.
Open the radiator bleeder plug slightly.
Keep eye on the tank level as the air escapes from the bleeder plug.
Wiggle the plug. You will start hearing the bubbling sound and once no more bubbles with steady seepage of the coolant, close the plug.
Top up the tank/funnel again and attach the clear tube to the heater core bleeder plug if you have later spec aluminium L-shaped pipe with the bleeder plug.
If you have very early model, it would be a rubber cap instead so you are very likely to revisit here later.
This is the most important area of the entire bleeding process because it takes ages for any air trapped inside the heater core.
Follow the same process as per the thermostat cover bleeder.
Collect
at least 1.0 - 1.5L of coolant through this specific bleeder.
With the early model rubber cap, you could use larger ID clear tube just for this process but if you don’t have one, revisit this bleeder few times after each driving session. Will touch on this later.
Top up the tank/funnel and repeat the same process at the bleeder on the heater return pipe (eng bay firewall).
Top up the tank/funnel and repeat the same process one more time at the thermostat cover bleeder but on this occasion, collect enough coolant so that the coolant level sits just above the MAX line.
With this process, you can remove majority of the air inside the system.
Double check that the bleeder plugs are all closed (and the rubber cap + clamp for the early model).
Close the tank cap to the 1st notch (not fully closed).
Start the engine and keep eye on the coolant level as well as the temperature gauge.
The coolant enters the radiator from the bottom side.
Until the thermostat starts opening, the lower rad hose or the rad body itself would be cold.
Once the thermostat starts opening, you can start feeling the rad body getting warmer.
At this point, you could squash the big coolant hose at the thermostat cover.
You may be able to hear the float/jiggle pin of the thermostat moving back and forth while any remaining air pushed back to the tank.
Keep eye on the temperature gauge and the coolant level.
Wait for the rad fan to kick in.
Depending on the air temperature, it can take
more than 20min after starting the engine so be patient.
If followed the above entire procedure, never experienced but if the needle gets even slightly above the normal level or the coolant level getting close to the neck, stop the engine even before the rad fan kicks in.
From what I heard, this situation can happen on the early model with the rubber cap at the heater core bleeder.
No damages done but you didn’t bleed the system enough.
Too much air still left in the system so you want to bleed the air further
ONCE the engine has cooled down.
If you didn't experience the higher temperature situation or the potential overflow from the tank, let the engine run for several minutes after the rad fan kicked in and then stop the engine.
Park the car overnight and check the coolant level.
Top up the coolant if required to set the coolant level at MAX line.
Now ready to take the car out for the 1st test driving session.
For the test driving session, even in the hot summer, I’m afraid you want to keep the A/C CCU temperature setting at higher temperature range to keep the water valve open.
I always set the CCU temperature dial at max but keep the fan speed to min for at least 5min during the test driving session even during the hot summer.
Park the car overnight.
Now time to revisit the heater core bleeder.
This is especially important for those with the rubber cap bleeder.
While the engine is cold, remove the tank cap.
Now crack open the heater core bleeder or lift the rubber cap just enough to let the air/coolant escape from the L-shaped pipe.
If no air or just tiny amount of aerated coolant, good news and no problem.
If you hear just hissing sound with no coolant for like 1sec followed by the coolant, you may need re-visiting here again for the next few outings.
Adjust coolant level, close the cap and done.
Unless you track regularly with the aged radiator, you should not need topping up the tank until the next coolant service.
I never touch the coolant for the next 4 years using the OEM Type-2 coolant.
It can go for 5 years but I prefer slightly shorter service interval.
There is no need adding any chemicals or the use of different type of coolant.
If cooling efficiency is the highest priority, just use plain water.
No rust inhibitor or WP protection though….
If you think the coolant never boils even under perfect condition, imagine how high the temperature gets at the surface of the cyl water jacket and what happens with the coolant at the surface while pushed by the force of the WP.
Never recommend doing this but think about what will happen if you quickly put your hand in and out of the liquid nitrogen. That’s one side of the cooling system.
Kaz
