I have audi a4 sport tdi 2002 I'm not a mechanic. I bought car 2 months ago guy told me there was a coolant leak at bottom of tank it's overflowing  cut a long story short there's to much pressure in cooling system  I've changed thermostat also put kseal in collant shortly after putting kseal in loads of foam in expansion tank. Could radiator be blocked car is now overheating but goes back to normal temp heater blowing hot and cold and losing coolant anyone have any ideas I'm puzzled

Hello, You will first need  to get the cooling system pressure tested- and report back on the findings. One can easily jump to conclusions, but let’s wait for the result of that test first. K Seal? Not a good move, although I have  seen some good results once, and with a low compression tractor! 

Kind regards, Gareth.