I have a 2004 DeVille, 4.6 liter VIN Y engine, it has 159,000 miles on it. I think I am having some major problems developing with my cooling system. For a few weeks now, I have been getting "Check coolant level" on the notification panel after each time I start the car. This message has appeard even when there is coolant in the surge tank. Up until today, everything seemed to be fine otherwise, it wasn't overheating or anything. However today when I was driving it, the heat was not working at all, except when I was driving it down the freeway at 55+ MPH. When I slowed down or stopped at a red light, the air coming from the vents got cold again. When I sat in park and revved the engine, the air was still cold. Then when I got close to home, I noticed the temperature gauge was starting to creep up 1 and 2 bars above the halfway mark, which it doesn't do normally.

When I went under the hood I removed the cap on the coolant tank slowly and it sounded like there was a lot of pressure build-up, then when I got the cap off, steam was coming out. The radiator fans sounded like they were running like they should be.

I have had to fill the coolant tank many times over the last few weeks. Not sure what is going on. I have had this car for four months. I hope it isn't the dreaded head-gasket issues that are common with these engines.

I would pressure check the system and look for external leaks before you condem the head bolts.

Let it sit over card board to narrow it down. If it is saying that the level is low when it'* not sometimes it'* crap on the sensor, and can be wiped off