Mondeo Overheating

[jimcognito]

Hi. Have recently got myself a 1998 mondeo 2.0 6v zetec. I noticed it had a slow water leak from the thermostate housing. It also required a new rad, as the old one had split at the top. I replaced the rad and will be sorting out the other leak very shortly. The problem is that after replacing the rad, the car over-heated very quickly, far quicker than with the damaged rad. I have very limited knowlege of fixing cars but i would hazzard a guess that this is due to that fact that now the radiator doesn't leak, there's nowhere for the pressure to release? So my question really is: Could it be the thermostat housing (or a part inside it) that is causing the overheating and maybe stopping the circulation? I also noticed that when i loosened the lid of the filler cap, it bubbled away frantically like a witches cauldron which led me to thinking that, for that much air to bubble, the water isn't circulating properly (if at all). I do realise that this could be the water pump but don't want to jump to too many conclusions as my brain is now hurting Any advice welcomed.

[Lincoln_white]

I'm no expert but if it over heated without loosing water then i would look at the thrmostat first. i think if water pump gone then they leak because its normaly the bearings that go in them. i've never had a car air lock so not sure if they do.