Coolant and Heating overheating causes and fixes

Split hose from header to top-up tank

Mocki ok, how it works:

Top up tank to fill mark, when engine cold.......

Engine gets hot, coolant expands, builds up pressure with temp, and opens header tank pressure cap (VW Blue, after market black, Dalek shape, left hand rear of engine bay) forcing coolant into the top up tank........

Engine cools down when parked, coolant contracts, pressure turns to vacuum, and coolant is sucked back from top up tank to header tank, returning top up tank to fill level from its over full state when hot.....

So, if the pipe between is split or leaking, it would be pushed out of the header tank and out of the split pipe onto the zorst, not into the top up tank, and when the engine cooled down, the header tank would be not full.......

However, if you overfill the top up tank ( fill it when cold with Coolant at least 50/50 mix with water) it will push excess out of the breather holes in top of the top up tank, onto the zorst, and find its correct level.....

Mocki again!

the header tank is the one with the darlek cap on, inside the engine bay the top up tank is behind the (infront of) the number plate flap.

the header tank should always be brim full the top up tank should be between the marks depending on the temp when you check it.It has vent holes in the top of it, so if it gets over full it vents out the top

the coolant is pushed out of the headertank into the top up tank, and sucked back ( through the same pipe and cap) when the engine cools and the pressure turns to vacuum, in basic terms.

so if the top up tank is empty it has nothing to suck, but will still blow into there.

it is a one way valve as such, pressure forces the coolant past it , but it allows vacuum to draw it back.