lexus-is2

After bleeding and burping the coolant, if after a while after its cooled down, I close the pressure cap and then few hours later I came to open the pressure cap and notice the coolant is not right at the top but I can still see the coolant but it's just not right at the top, does that mean by me opening the pressure cap I've now let air back in the system because the coolant isn't right at the top?

DennisMik

By design, the radiator will suck coolant out of the overflow tank as it cools off as long as you have the radiator cap on. By leaving the radiator cap off, the coolant cannot create a vacuum as it contracts and will not refill itself from the overflow reservoir tank
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You don't have to fill the radiator if you don't want to/feel like it. The next time you drive the car and the engine heats up to operating temperature, the coolant will expand and fill the radiator. Then when you turn off the engine and the coolant cools and contracts, it will suck coolant out of the overflow tank as long as you have the radiator cap on.

ELexis

Additional coolant flush information located here;

Coolant System flush
https://www.clublexus.com/forums/is-...m-flush-2.html

lexus-is2

Thanks for the replies. Question, I'm trying to understand this. So the overflow bottle allows the expanding excess coolant to come to the bottle as it has nowwhere else to go. This I believe is done by the radiator pressure cap which opens up the path to let the coolant into the bottle when the pressure exceeds it's limit. So if pressure exceeds it's limit it means coolant has expanded and needs to go into the bottle? But then the part I don't understand is that when cooling down and the vacuum that is supposed to suck coolant back into the engine from the bottle, how is the path the bottle open if the pressure cap valve only opens when pressure is reached? If that was the case then there will be no direct path to the bottle because the pressure isn't there.

ELexis

The radiator coolant overflow tank works by filling the tank with coolant when the cooling system’s pressure is too high and withdraws coolant from the system when there is pressure in the system. The coolant is transferred back and forth between the overflow tank and cooling system depending on the pressure.
This design works fine, as long as your coolant doesn’t get too hot. As the coolant heats up, it expands. In a sealed system, however, there’s no room for the liquid to expand. This can cause a problem as an over-pressurized system can cause your liquid to boil faster and to burst through any weak points on the system.

This is the reason why vehicle needs to have an overflow tank as the pressure inside the coolant pipes increases due to the coolant solution being heated and therefore expanded. The expanded coolant needs somewhere to go. Any coolant that no longer fits inside the primary cooling system is now forced into the overflow tank, where it’s stored until the engine coolant temperature reduces. As the coolant begins to cool, it contracts and increases the amount of room once again inside the cooling system. This contracting of the coolant creates a negative pressure which draws the extra coolant stored in the overflow tank back into the primary cooling system. The overflow tank is used as an expansion vessel to allow the coolant mixture to expand and contract as it warms and cools, without over pressurizing and damaging the cooling system.

If you’re seeing an overflow occur via the overflow coolant tank tube, it could be due to a defective radiator cap, thermostat, water pump, radiator issue or due to overfilling the system. When the pressure of the coolant in the radiator surpasses the designed pressure of the radiator cap, the coolant passes the radiator cap seal and flows into the coolant reservoir overflow tank through the overflow tube.

* The thermostat blocks the flow of coolant to the radiator until the engine has warmed up. When the engine is cold, no coolant flows through the engine. Once the engine reaches its operating temperature, the thermostat opens. By letting the engine warm up as quickly as possible, the thermostat reduces engine wear, deposits and emissions.

Protholl

The radiator cap on the 2IS fails fairly often. If you scan the forums you'll see people recommending replacing it. I'd start buy purchasing an OEM radiator cap and see if it makes a difference.

DennisMik

The coolant overflow tank was required to be added to cars with the implementation of pollution laws. Since water expands when it is heated up, it needs extra space. On cars 50 years ago, the coolant would spit out on the street.

The radiator cap is a 2 way valve. When you look at the radiator cap, you see a big spring in the center. This spring is what seals the radiator tank. It presses the rubber washer down over the opening of the radiator filler neck. This spring is also the device that determines the pressure that the cooling system will run at. As the coolant warms up and expands, the pressure in the cooling system (of which the radiator is part of) increases and the pressure will push against the radiator cap and compress the spring, allowing the hot coolant to escape the radiator and flow into the overflow tank.

As the engine cools down, the coolant contracts in volume. This creates a vacuum (negative pressure) in the cooling system. On the very bottom of the radiator cap is a small metal button about the size of a dime. This is the 2nd valve. The vacuum in the radiator pulls the metal button into the radiator, thereby opening the radiator cap to allow coolant in the overflow tank to go back into the radiator.

Pressurizing the cooling system is a good thing because it raises the boiling point of of water. The 13 - 15 pounds of pressure raises the boiling point of water to around 240º F. The chemicals in the antifreeze also raise the boiling point. When driving the car, the coolant temperature goes up and down between 185 and 200º F. When you have the air conditioning on, the coolant temperature runs between 210 and 215º F. The cooling system could be made to operate with a higher pressure and run at a higher temperature, but overall the engine would not benefit from higher temperatures. To operate at a higher pressure, you have to make a stronger container. The weak points are the radiator and the hoses.