Low Coolant Issue

The low coolant light keeps coming on in my 2001 Grand Prix SE 3100. It fluctuates on and off just after I start the car. At operating speeds it stays on. The coolant reservoir is full. The heat is also acting kind of funny. It doesn't heat up as fast as it usually does. While warming up, the temp gauge will go up to 210 and then drop down to almost cold again. A few minutes later I have heat and it sits at a normal temp. The car does not overheat.

Any thoughts?

To start instead of relying on the coolant reservoir for proper coolant level with the engine cold check the coolant level at the radiator. After radiator cap is removed coolant should be at the bottom of the filler neck. If thats good and no confirmed coolant loss you can remove the level sensor and try cleaning it. Located about 3 inches below the radiator filler.

Also, when was the last cooling system service and are you still running the original Dex-cool coolant? Were the lower intake manifold gaskets ever replaced with the revised ones?

To start instead of relying on the coolant reservoir for proper coolant level with the engine cold check the coolant level at the radiator. After radiator cap is removed coolant should be at the bottom of the filler neck. If thats good and no confirmed coolant loss you can remove the level sensor and try cleaning it. Located about 3 inches below the radiator filler.

Also, when was the last cooling system service and are you still running the original Dex-cool coolant? Were the lower intake manifold gaskets ever replaced with the revised ones?

I'm still running the orginal coolant. I just it 100K and was going to have it done at my next oil change.

I didn't receive a notice about upgraded gaskets. Was it a recall?

I would replace the Dex-cool since it is due anyways and many would say overdue since you have a 2001 model. Either with Dex-cool or aftermarket coolant like Prestone Extended Life. Dex-cool is supposedly only good for 5 years or 150K miles, whichever comes first.

Visit our Tips & Maintenance forum which touches on the 3100 VIN "J" LIM gaskets. See link below. It was never a formal recall or GM voluntary recall but covered in a GM TSB dating back several years. If you get any Dex-cool sludge it may interfere with the operation of the level sensor. Also, any air may cause erratic operation so you should ensure the cooling system does not have any air which can be bled out.

http://www.automotiveforums.com/vbulletin/showthread.php?t=688015

Note: Flush cooling system of old Dex-cool before adding new and be sure to bleed any possible air out.