finally got my tax and mot earlier, so my RS is now fully legal, so i went out for a drive, not booting it, just taking it steady........ but after i got home i let the car idle to cool down, but i decided to let it idle for alot longer (15 mins) to see how hot the new engine would get, the needle didnt move over half way or there abouts but all of a sudden i had a load of steam start coming out of the bonnet, the temp gauge was still normal, but when i popped the bonnet i found i had a small crack in the top of the header tank (expansion tank), where the steam/water was spraying from.

could this be caused by the car running too lean/rich on idle??? the revs are also a bit low on idle. i will be getting the fueling checked/setup tomorrow @ Race Power Motorsport (norfleet, kent), but not run up for atleast another 500 miles. I need to know if the idle fueling could have caused this or could there be something else? it had a new head gasket and head bolts fitted recently, so i know these are fine, and i done a compression check after fitting the engine a few days ago, all was fine and in uniform.