Heat comes and goes 99 Chevy Malibu TEMP COOLANT LIGHT COMES AND GOES WHY?

Thermostat's starting to stick. Needs replacing a.s.a.p.

Most Malibu with the 3.1 engine have the same problem and it's your intake manifold gaskets that are probably bad... Intake gaskets are located in the middle of the valve cover and reach the bloc (V). Look with a flashlight near the bloc under the thermostat housing (rear) and behind the power steering pump (front)if you see coolant in these areas your intake gaskets are probably bad. Check engine oil dipstick for indications of a milkshake and high level of oil... on my car, oil was clean but changing intake gaskets solved the coolant slowly leak problem. Before attempting to replace your intake gaskets, have your head gaskets tested by a mecanic. Because if they are bad too (will appen if you wait before solving the problem and that your engine overheat too much), one you have reached intake gaskets, it's not verry complecated to to replace them too. Only exaust manifolds will be on the way before removing the heads. If they are good, just search for the procedures on sites like autozone.com or search in Google... on how to replace intake gaskets. I've already written the entire procedure I think on this site. I'm not a pro and I've done the job myself. Have your cooling system bleeded by a mecanic after you've done the job... By doing it yourself, you'll save hundreds dollars!