Started to over heat on the way home

So stopped at heathcote to check it out. Pulled the rad cap off. And it let out abit of steam (mm that cant be good). Anyway top it up and it dont like that. keeps on spitting it back out.
Well my old TD42 shorty used to do this when the thermostat died. So I pulled that out. Went to to fill.
MMM still spits water.
Anyway said

Anyway it runs fine until I get to Bendigo (another 40k's) Then heats up again.

So pull over at the servo and go thru the routine agian. Where it doesnt like water (it spits it out).
So I put abit in throw the cap on drop the bonnet and drive off. And the darn temp drops again. And only starts to rise agian when I pull into the drive way.
And dont get me started on the magna (other car).