Q&A

When you say there are white gases coming from the engine do you mean it's white smoke from the engine. Just wanted to be sure I know what you mean. If it's white smoke there is almost no way not to get coolant or oil on the exhaust while performing the head gasket repair. As for the temp gauge the Engine Coolant Sending Unit may not have been plugged back in or it was damage while the work was performed. It sounds like you know what your doing so go to a auto shop website and look what the coolant temp sensor looks like and find it on you car to make sure of it being connected. Engine coolant sending unit, which is the single wire post goes directly to the temp gauge on the dash.
Try this link it looks very helpful as someone else had your same problem.
http://autoforums.carjunky.com/Automotive_Repair_C1/Elect...