Hi there.

Would anyone know where to buy exhaust j-tubes in australia for my 2.0 type 4 engine as my heater boxes are dead.

Go vintage speed, they make a nice equal length set or for a bit less cash unequal.

VVDS have them in stock Sydney 02-9789-1777

I want J tubes too but heard they affect the engine temp, as the heater boxes are also designed to take heat away from the engine. Can anyone confirm this?

only when the vehicle is stopped and it will be minimal as the cooling air from the engine is pushing the heat away from the exhaust

you wont be able to measure it