KuroNekko wrote:That hole you see is the boil-over relief outlet. When the coolant boils, that is were it can escape out of. Nearly all cooling systems with an overflow reservoir have this. Some have hoses, but they merely go downwards and have an opening. These holes are always located at the top of the tank.
While I'm not sure, they may also act as air bleeders. The reason why I think this is because cars that have a pressurized reservoir tank (Mazdas, Fords, and many GMs) don't have radiator caps. You fill the coolant via the pressurized coolant reservoir. They have air bleeder valves specifically designed to purge the air from the coolant system once you add coolant.
I have not seen many traditional cooling system with radiator caps have these bleeder valves as the radiator cap opening is typically used to bleed air. I believe the overflow tank relief hole can also purge the air if it makes it to the overflow reservoir.
After each drive, check the coolant in the overflow tank right after you park.
Also, when adding coolant, add it directly to the radiator if it's low, not the overflow tank.
To keep it simple, lets just stick to the Kizashi.
The coolant recovery system is a standard system, which allows part of coolant to flow from the radiator into the coolant reservoir when it is expanded by heat. When the cooling system cools down, the coolant in the coolant reservoir is drawn back into the radiator.
So, the engine cooling system and radiator are pressurised, the overflow coolant reservoir isn't. There will be an overflow hole in the reservoir, but coolant will only be expelled from that hole when there is something wrong with the cooling system (it could be as simple as it being overfilled.)
Coolant level check and top up:
Coolant Level Check
WARNING:
To avoid getting burned, do not remove radiator cap while engine and radiator are still hot. Scalding fluid and steam can gush out under pressure if cap is taken off too soon.
When engine is cool, check coolant level in reservoir (1).
Normal coolant level should be between FULL mark (2) and LOW mark (3) on reservoir (1).
If coolant level is below LOW mark (3), remove reservoir cap (4) and add proper coolant to reservoir to bring coolant level up to FULL mark (2).
It is not necessary to remove radiator cap to check coolant level.
You should be checking the reservoir level only after the vehicle engine has completely cooled - this will take a long time. Best to leave it over night. That will allow for the engine coolant to contract- sucking back into the engine any coolant that has overflowed due to expansion with heat. It's a waste of time checking the reservoir level when the engine has just been stopped- unless you're purely looking for over flowing or bubbles entering the reservoir from the radiator overflow.
Amoows should also never need to remove the radiator cap to top up the engine coolant. In a Kizashi, any air in the engine cooling system will bleed out through the reservoir- with the natural expansion/ contraction cycle of the coolant. The coolant expanding will force any air, past the pressurised radiator cap, into the reservoir. When the engine cools, the reservoir is designed to only allow coolant to return to the engine (providing the level is kept between the high and low markers.)
So, continually getting air in the system- or the coolant level in the reservoir always requires top ups- indicates a problem..... It could be something simple like the radiator cap not being done up properly (or a deteriorated seal letting air in during the cooling cycle) to something more serious like a coolant hose leaking or head gasket leak!
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