expansion bottle level

hi guys just been out fiddling , fired the car up , but noticed before that the coolant bottle was almost full now normally its at the lower mark , anyway left the car running for half an hour temp guage in the middle but bottle still high , could it be the stat not opening ?, again temp was ok .

thanks peter

well ive just took about a litre out , give it a good run and it seems ok temp guage is normal

When it's cold and on the level it should be at the max mark, as the name suggest it's a expansion tank and the cooolant expands up past the max mark but it is designed to do this that's why the max mark isn't at the top.

So to reiterate under normal conditions it will rise above the max mark as this is how it is designed to work.

Essentially though if, when cold, the coolant is to the brim under the actual rad cap, then what's in the actual expansion tank is not that important

Essentially though if, when cold, the coolant is to the brim under the actual rad cap, then what's in the actual expansion tank is not that important

Really ? Are you sure about that ? so if the tank is empty and pumps air into the system then that's not important ?

was always told years ago when i first had the car that the level should always be low , and most of the time its been like this , but for some reason today it was full, so wondered why , i took out over a litre from the tank so it was back on the lowest mark went for a run , got back let it cool down and it was still there . so a bit confused as to why it filled the tank ,

Is your rad cap ok

The expansion tank as long as its got some in it when the system is cold it will work correctly but its best to keep between the min & max

Basically

If the tank is too low when the system is cooling down then it will draw air into the rad via the expansion tank, if its full as the system is heating

up it will simply overflow the excess fluid and not a problem

Really ? Are you sure about that ? so if the tank is empty and pumps air into the system then that's not important ?

If it's cold and the tank is empty but the rad full when you run the car what happens? the heat/expansion means the coolant will flow from the system in the expansion tank, when it cools it should flow back. I'm not saying ignore your tank completely I'm just saying the specific level ie top middle or bottom isn't crucial. Whatever level your car sits at should be fine, continual loss and any sign of a 'non brimmed' state in the actual rad need investigating.

ok mate as said its normally on or around the low mark, never empty , but yesterday after id been doing something noticed it was full , i run it for a bit but it didnt go down