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

OEM Coolant Header Tank

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On several occasions, I had to work on NSX with aftermarket coolant header tank (or Expansion tank) and also asked from many owners regarding the use of aftermarket one.


Although they look nice, I saw several issues such as cap not secure enough, leaking coolant due to crack at the welding, design issue with tank expanding under pressure, etc.


As far as I know, I have never seen an aftermarket header tank designed and tested to the same level as the OEM one.
Having said this, I won't say OEM one is perfect. In fact, in my view, it has serious issue of not being able to check the coolant level without removing the cap or without the support of flashlight from behind after the tank was used even for just one year or so. It turns into creamy white colour making it impossible to see through the coolant level.
In some countries, the law requires the driver to check several points on the car including the coolant level before start driving so one has to be able to check the coolant level wth ease.
If the engine to be started while it's still hot, the driver can't remove the cap and has very limited option on checking the coolant level on NSX.


None the less, it's well thought after and well designed structure.





NSX uses higher pressurised (1.1kgf/cm2) system than the ordinary production cars (0.9kg/cm2).
Therefore, it requires careful consideration on the size of single wall/plain against the high pressure for many years.
For this reason, the OEM one has rounded body including each corners and it has been separated in 6 chambers internally to reduce the size of single wall.
The internal walls are integrated to the outer wall and together with the rounded wall/corner making it very rigid against the pressure.


This is the same between the upper and lower tank structure and these two are bonded at the seam (where it can start leaking after many years).


The other most important feature is the air/fluid separation for cooling efficiency.
I'll leave the detail for now but many people spends too much time warming up the engine first thing in the morning and don't pay much attention on stopping the engine.
In UK, even in the cold winter, you only need a few minutes to warm up the engine before start driving very slowly. While warming up the engine, you are actually circulating the blowby gas contaminated with the moisture inside the engine and making the engine oil to trap it for you. So far, from what I have seen in this country, I saw much severe damages to the engines with the low annual mileage NSX than the ones used regularly. Obviously, the total number of issues are lower on the low annual mileage one.


It's much more important to let the engine and other parts to cool down after driving on the motorway or A/B-road by keep running the engine even just for a few minutes at idle rpm before shutting off the engine.


Still, as a production car manufacture, Honda had to deal with all sorts of driving style/conditions so inevitably, there will be a case where the coolant could boil at the cyl wall and thus, air/fluid separation becomes key feature for the header tank.





Addition to the cleverly designed/structured six chambers at both the top and bottom tanks, each chambers are connected at the small single hole located near the bottom of the internal wall. The coolant will pass through each chambers only through this bottom hole and the air will be separated as it will float upward and separated to the upper chamber. Even the six air chambers at the upper tank are connected each others with small hole at the upper side of the internal wall. What a complicated and sophisticated design.


By the time the coolant reaches the last chamber, the air is completely separated and only the coolant will be returned to the engine.


I have never seen the internal structure of the aftermarket header tank but looking at the position of the welding and using flat aluminium plate body/wall, I don't think it has multiple internal wall structure for air/fluid separation purpose.
Unless it's using really thick aluminium plate, I don't know how it can cope with the very high pressure per panel over many years without internal wall supportor or the rounded design and with the sharp edge/angle bonding design, not sure how it can maintain the constant thickness at the welded area.


I'm not against the use of aftermarket parts and there are lots of nice and well designed parts available on the market.
Possibly the same for the header tank and I just don't know such product yet.

Despite the issues mentioned above, I'll stay with the OEM header tank for my NSX.....



Kaz



(All photos from Mr Toyoizumi at KSP Engineering, Japan)

Updated 22-07-2014 at 10:15 AM by Kaz-kzukNA1 (Updated the font)

Categories
Parts , Cooling

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