Thanks for the replys guys As far as using mobil1, thats what AVA put in it when they serviced it and going by the sticker that was on the front panel, PJ Motorsport used that also when they rebuilt the engine. I will keep an eye on it and see how it goes.

As for the hissing from the cap, i will check the tank and cap for cracks and i will also empty some water out, the tank doesnt have a min or max mark so its hard to tell where the level should sit, i defo think i put to much water in it though.