Low coolant.
 

So I have a 2002 SS 3.8 LT V6, and whenever I drive more than 5 miles or so, my low coolant light turns on. Has this happened to anyone else, and if so, how do I fix it? A friend of mine said it may be the sensor, but I figured I'd ask you guys first. Any info would be appreciated. Thanks!

Is coolant low when the light comes on or not? If it's not low then I would say the sensor is bad, if coolant is low when the light comes on then it's either leaking coolant or burning coolant which needs fixed asap

Exactly as turbo mentioned

Also with low coolant in the radiator you can tell when warming the car up, when it's warming up in idle it doesn't blow HOT air maybe warm but never hot like it should (until you start driving) That's one way you know before you open the radiator cap you're low in coolant.

Use DexCool 50/50 if you need to top off (the orange coolant)

Add directly to radiator when it's cold best in the morning before warming the car up. Also after filling the radiator top off the reservoir to the cold level of needed

I have a 2002 Monte and my low coolant light came on when the coolant was not low. So I changed the sensor and the light went out for about a month and then came back on. Not sure why but I am going to get the radiator flushed real good and see if that fixes the problem. Only 48,000 miles on the car but it has sat in storage a few times.

Oil in the coolant from a leaking lower intake manifold gasket or transmission cooler leak can turn to sludge and coat the probe on the coolant level sensor causing a false reading. You can clean or replace the sensor, but it's really hard to get rid of even with a radiator flush. Always seems to be some residue that doesn't go away and the problem comes back. A sign of this is sludge under the radiator cap and around the neck. If you do see sludge find out where it's coming from before you flush the radiator or will just come back. If your car is an SS with 3800 series 2 engine my guess is that the car still has the original plastic lower intake manifold gasket which is prone to failure. It should be replaced with a metal reinforced one made by Felpro. I would also recommend replacing the original Upper Intake Manifold while it's off with a Dorman one that has a metal sleeve to reinforce the plastic port that tends to get melted by hot EGR gas.

Thanks plumbob. I think you got it. Took the cap off and sludge around the top of the radiator neck and cap. I'm surprised we didn't notice this when we replaced the sensor the last time. Likely a sign that it is getting worse. Definitely need to fix the problem before I flush and replace the sensor. Thanks again for the advice. I'm sure you saved me the time and frustration of flushing and replacing only to have it recur.

You're welcome.
Keep us posted on the project.

Took the monte in today to have it looked at at my local shop. He said he thinks it is just the dex-cool which he said will do that. Hmmm. Never heard that before. He wants to give it a good flush and he thinks that will do it. I had already cleaned the sludge around the cap and neck so he didn't see that although there was still some there. Think I will look for a second opinion.

I also have a 2001 Pontiac Grand Prix GTP and had a recall notice on that some time ago about a faulty gasket. So on lark I called GM to see if there was a similar recall on the Monte. The women I talked to said that there was a pending recall on the Monte to do with a gasket. I told her about my coolant issue and she said she thought that this recall might deal with my issue. Keep in mind I wasn't talking with a mechanic and she couldn't tell me much about the recall but it is pending and will be sent out shortly. I think I will wait for that before chasing this issue further.