Anyone know why the coolant in my system goes into the reserve tank like it should when it's hot but it won't go back into the radiator when it cools down.
Radiator cap is the correct pressure rating and the hose from the radiator filler neck to the reserve tank is not blocked.
Cheers
So you are saying that the water level in the overflow tank never drops?
It could be normal that it never completely empties the overflow but if it doesnt go down anwhere as much as it fills when its hot then there is an air leak.
Where are the likely places?
1] Primary suspect is the radiator cap seal under the cap/handle of the cap. The cap neck seal may be OK and blow off at the correct pressure but the top of the cap must also seal against the top of the neck both under pressure and a slight vacuum.
2] The water pump seal can allow air in as it is only the spring that holds seal face together. Once pressure has built up in the cooling system the pressure also forces the sael against the sealing face.
3] As mentioned in another post above a clamp on a connection to the expansion tank could be loose or it could also be too tight and cuts the hose or worse deforms or splits the nipple that the hose is fitted to.
4] If you have to top up the radiator look also at heater taps as sometimes the leak is not obvious but if you are using the GM coolant it generally leaves a telltale stain.