Water coming from engine into overflow tank

Two cooling fans controlled by three relay's . If only one fan is working ,that could be a problem .
Coolant Level Sensor Description
The coolant level sensor monitors the coolant level in the cooling system and indicates if the coolant is low. This sensor is located at the base of the radiator surge tank and is not serviceable.
CHECK COOLANT LEVEL (2)
The IPC receives a discrete input from the engine coolant level switch. The engine coolant level switch is normally closed. When the engine coolant is low, the engine coolant level switch opens. When the IPC receives an open signal from the engine coolant level switch, the IPC displays the message on the DIC.

Relay Driven Dual Cooling Fan Diagnostics There are using a pontiac , by your cadillac is the same .

Is it antifreeze or just water? If water, your AC system will frost up under use, which will melt and pool under the car on the passenger side (normal) after the engine stops. If antifreeze, there is a complicated cooling hose system, with some of them near the firewall. Check the overflow tank to see if you are losing coolant, and if so, check the hoses there while the engine is running.

Depending on where you live in the country, 212 isn't to hot. Your high temp fans don't come on until 225-230. And what you described sounds normal as there is pressure in the system at 124.

Click the link below for details regarding this problem:---http://repairhelpcenter.blogspot.in/2012/02/water-flowing-back-into-overflow-tank.html--------Thanks.

Well there are a lot of things to look for and they are .
1st the engine would sound differant slight hissing or running a little rougher on idle or pick up.
2nd if head gasket is starting to blow between 2 cylinders then you will get a back firing through the exhaust or carby {depending on what cylinder is blowing to what cylinder} and if you are loosing water then you will see it in steam form coming out of the tail pipe of the exhaust and engine could be breathing steam back into A cylinder which would also make it run a bit rough.
BUT IF all the cylinders are running well and you are loosing water and cannot find the cause then it could be blowing out of the overflow tank on the side of the engine,and check on the thermostat as that can alsogive you the same problems.
So let me know how you get on
Ron.

The most common overheating problem with the Northstar engine is a blocked purge line. It's job is to purge air out of the cooling system.
There is a small diameter hose coming from near the top of the coolant tank(not the cap),this is the purge line.
With the engine idling,pull the purge line from the tank,if there is no coolant flow from this small hose,it is blocked and this will cause overheating.If the hose is clear, check for blockage at the nipple on the tank.Or trace the hose back until you find the blockage.The hose goes in to the engine to a crossover and comes out the other side to near the thermostat housing,the blockage may be there.

The thermostat could be bad. Run the engine cold with the cap off the bottle. If it comes out while the engine is still cold, you have a bad headgasket. Otherwise, start by replacing the thermostat.

Overheating can be numerous things: Fans not working, water pump, thermostat, overflow cap, and the list keeps going. When the engine is running and heats ups, feel the heat of the top hose, if the hose isn't hot, the thermostat is most likely stuck open and needs replaced. If it is hot we know you have circulation. The cap on the expansion tank may be defective, if it can't hold the pressure of the water, it will release at the overflow cap if the cap is bad. Also check the coolant level.

flush your radiator first.with the thermostat out you should see the water moving if not bad water pump.this engine needs the thermostat to function properly and either a 50/50 coolant or straight coolant so it does not boil over.also make sure your fans are coming on

Yes. I have done it many times.