question........ since the top of my coolant overflow leaks. is that why the bottle is full? not sure how the radiator works, but does the overflow constantly change up and down? coolant gets sucked in and out? enlighten me please.


thanks!

 

When the cooling system is pressurized, coolant levels in the reservoir may go up or down depending on the state the cooling system is at. At normal operating temperatures the reservoir will generally stay at about the same level as if the system was not pressurized (for example, cold). If the car rise above normal operating temperature, due to increase pressurization, coolant level in the reservoir may rise above the Max fill line. After the car cools down some, some of the coolant in the reservoir will be suck backed into the radiator. If your car overheated and coolant came out of the reservoir, the reservoir level may be lower than normal once the system pressure is lowered.

The reservoir should be checked and filled to the proper level when it is cold and not pressurized. Filling to the Max fill line (the Max fill line is not the top of the bottle; there is a marked line) when cold is okay and proper, this helps to compensate for evaporation or any minor loss of coolant such from a slow leak and reduce chance of overheating before the serious damage occurs. Routinely checking and topping off the level of the coolant to the fill line should be done.

 

As redbull said, as the coolant heats up it expands, the expanded fluid flowing into the overflow. As the engine cools, the coolant contracts and the system refills from the expansion tank. As long as the level is between the min and max level regardless of engine temp, you are ok. Usually, when the engine is cold, it's nearer min, when at normal temp, it's higher (how high is dependent on exact engine temp).

A couple of things to look for. If the expansion tank continues to fill to overflowing, it could simply be a sign of over filling the tank. First thing in the AM check the level. If it's near or over the max line, this is a sign.

Sometimes the radiator cap can be defective, and not sealing the system allowing it to pressurize. This can also cause the expansion tank to overflow. Of course there are other things, but overfilling, and a bad cap, are the most common.

Caps are very inexpensive so you might try to replace it if overfilling the tank isn't the cause.

Here is a pic of a cap


If either of the seals are bad, or the vacuum relief valve is not sealing or missing (happened to my step sons car) , you need a new cap.

 

Also check for nicks or gouges in the 2 rims around the radiator neck, where 2 of those seals press. The "top seal" uses the upper rim of the radiator neck. The "Pressure Relief seal" uses another ridge or rim down inside the radiator neck.

 

this is a brand new radiator and cap.....this was the day after i put it in, i had the overflow.....i'm having starter issues, so it's been sitting for 2 days...i'll check out the level of the coolant tomorrow morning when it's cooled down.

 

Is it possible you got the wrong cap for your radiator?

 

Now that's never happened...

Ya, there are two different caps, both with "install", but only one will seal correctly. I would double check that you have a properly fitting cap.

 

all's well on the rad and cap....... weird, I still think I need a new bottle...... update to come...