jj71787

Lately my water coolant light has been coming on and staying on. There is water in the car though.

Also the temp gauge goes all the way to the red when driving and then will slowly go back down. The car is not over heating. There is no smoke on the engine.

Injuneer

How are you checking the coolant level - in the radiator, or in the reservoir?

An overheating engine does not necessarily produce "smoke on the engine". Proceed with car.... it may actually be reaching an excessive temperature, before the fans can pull the temperature down.

jj71787

I am checking from the reservoir.

After I shut the car off the fans do stay on for a bit too

Injuneer

Wrong place to check. You have to make sure the radiator is full. If something as simple as the plastic overflow tube is cracked, the radiator will flow coolant into the reservoir as the system heats up and the coolant expands, then as it cools down and contracts, it can't use the vacuum in the radiator to pull the coolant back out of the reservoir, so it pulls in air through the crack.

The low coolant sensor is on the passenger side radiator tank, a few inches below the radiator cap.

DocJhn

The coolant light sensor is on the radiator not the reservoir. So let cool off and check the level of coolant in the radiator, did you lose coolant for any reason? If so you may have to bleed the system with the 2 bleeders on the hose connections at the block. I would also change the thermostat as it sounds as if it is not opening at the right temp. GL!

Injuneer

There are no bleeder screws on the LS1 engine (98-02). The LS1 does not have the same issues as the LT1 (93-97), and its "reverse flow" cooling system.

jj71787

There's water in the radiator too. Could it be a bad sensor that's misreading the temp?

Injuneer

Is the coolant in the radiator all the way up to the top of the fill neck? That's where it needs to be.

Faulty coolant level sensor is a common problem. Coolant permeates the seal and corrodes the printed circuit board.

jj71787

The radiator is full.

Should I replace the sensor?

Injuneer

Only if you rely on it to monitor the coolant level. If you don't plan to use it you can unplug it and the low coolant light should go out.

jj71787

But the temp gauge is going into the red.
The car is not overheating. So wouldn't that be a sensor problem?

Injuneer

Hard to tell. You indicate the temp goes into the red, which you appeared to be writing off as some unimportant error with the gauge. The temp goes up, and it appears the fans come on and pull the temp down. The temp at which the fans come on is controlled by the program in the PCM. Typically the fans go on low speed at 226*F, and high speed at 235*F.

Perhaps the sensor is wrong, or perhaps you have something causing it to overheat.

In the earlier LT1 cars, the gauge is driven off one sensor in the head, and the PCM temp feed is from a sensor in the water pump housing. I don't know if the 99 LS1 has one sensor or two.

You can check the accuracy of the sensor(s) using Shoebox's guide:

4th Gen LT1 F-body Tech Articles

While the temp sensor resistance values are the same for virtually all GM vehicles, the description of the two circuits is specific to the LT1, but the principles are the same.

jj71787

I'm obviously not the best at cars when something goes wrong.
I'm just trying to get an understanding as to why this happened. I don't see why the car would say it's overheating. Wouldn't there be some kind of smoke under the hood.
I could only think of a bad sensor giving a misreading.

I asked my dad he said could be a sensor or bad wires.

Just trying to understand before I have to go to a mechanic. Rather know what it is and try myself

Injuneer

An overheating engine would not cause smoke under the hood, unless oil was dripping onto hot engine components, or coolant was leaking from the cooling system and smoking when it hit hot parts, or just from the sudden pressure reduction as it escaped the pressurized system, into atmospheric pressure.

That's why correctly determining if the cooling system is full is important.

Is there any sign of white smoke out the tailpipe after then engine fully heats up? You may also want to test for hydrocarbons in the coolant.

jj71787

There is no smoke out of the tailpipes.

How do I test for that? I haven't put any coolant in. Right now it just has water.