i'm having a problem with my 99 grand marquis. I was over heating and thought it was my fan, checked that it's working, then thought it was my thermostat, replaced that still having a problem, over the winter i had no heat at times made me think that it was the themostat so replaced that now i'm still over heating and i'm building so much pressure in the cooling system it's blowing the fluid back out the cap of the over flow tank. any ideas?