ok, There are certain facts of physics that dictate -->when temp increases, pressure increases with it...The "Expansion" initially caused by the temp increase while warming your car up to correct opperating temp,,, creates a higher pressure in the cooling system & the water expands,,, & as it cools, the water then contracts/shrinks (for want of a better term) as the temp in your car increases it will push water out cause you have filled the system when it`s cold & there`s no room for expansion.
As one guy said earlier (Cush was sort of right but for a different reason) --> he said that he fired the car up,,, then waited till it was pretty well at opperating temp & all the bubbles (bleeding) has stopped & then topped it up & fitted the cap... In this situation the whole system is allready hot,,, allready expanded most of where it would expand too, & once the cap is back on , then job done, it basically won`t push much more than that, maybe just a tad.... But if he checked it once it returned to cold again, i`ll bet my left testical that the level is low again, simply because physics dictates that the water will contract (shrink) once it cools again... & as it does that it sucks some air back in to the system taking up the space that once was filled with hot expanded water.
Other things take place here too,,, When driving around, the car will sit at it`s opperating temp, but once you turn it off, there`s no cooling effect for the last few cycles of the engine,,, it`s created heat, but that heat takes time to transfer to all the metal in the block,,, then to the water thru the bolck/head assy, then to the radiator,,, then thru the fins & out to the air,,, BUT!!!! You`ve turned it off, so it "heat soaks",,, Basically the engine temp rises significantly & isn`t actually being cooled directly after. hence the reason why later model cars have the thermo fans fitted, some using the temp sender to turn themselves off well after the engine has been turned off & this way it helps stop the heat soak,,, electric water pumps are also good for that sort of situation.
However, it`s not a problem,,, it`s quite normal & the std mini cooling system (if in good order) is well capable of looking after all that.
If you fill the system when it`s cold,,, it will push some out as it heats up & after your turn off the car,,, then it will cool & contract & the level will be low once more,,, leave it tho because once you fire the car up again, it will expand to being full again once it`s got back up to opperating temp
Got It!!!!!?????
This is all only if there`s nothing wrong.
other reasons it pushes water "CAN" be things like a blown head gasket, or cracked head or blocked radiator or thermostat stuck etc etc etc
If you have worries about it then the best thing to do is to have it checked but a mini specialist but also you could help it by buying one of the old skool metal "Expansion Tanks" (like mokes had as standard),,, these are very very good things & are worth their weight in gold. (flat cap on the radiator & pressure cap on the expansion tank) & make sure the hose between the 2 is clamped & evacuated of all air in that line. (otherwise it won`t work properly).
oky-doky? Easy-peasy?
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