Changed coolant mixing valve added coolant engine shut down on coolant level .started cotinued adding coolant to proper level. defroster working again turned off engine left hood ajar. next morning car won't start .instrument lights won't come on turning ign switch only sound is relay click at the fuse box.battery load tested and charged at auto zone. doors, ac, lights work

There isn't one !
Filling Procedure
Notice: Do not add cold water to the cooling system with the engine at or above operating temperature. Adding cold water causes rapid cooling, resulting in possible engine damage.
NOTICE: When adding coolant, it is important that you use GM Goodwrench DEX-COOL® or HAVOLINE® DEX-COOL® coolant. If Coolant other than DEX-COOL® or HAVOLINE® DEX-COOL® is added to the system the engine coolant will require change sooner; at 50 000 km (30,000 mi) or 24 months.
Notice: Do not use a solution stronger than 70 percent antifreeze. Pure antifreeze can freeze at -22°C (-8°F).
Important: This engine is not equipped with block drains, 2.5 L (2 qt) of residual coolant remains in the engine block.
Refill the cooling system. In order to ensure sufficient engine cooling, freezing and corrosion protection, maintain the protection level at -37°C (-34°F) or lower.
Start the engine.
Place the heater and A/C control in any A/C mode except Max and the temperature in the highest setting.
Allow the engine to continue idling until the lower radiator to water pump hose is hot.
Turn OFF the engine.
Allow the engine to cool to outside temperature. Ensure the coolant level in the surge tank is at the proper level (1).

Refilling Procedure




Notice: When adding coolant, it is important that you use GM Goodwrench DEX-COOL?"¢ coolant. If coolant other than DEX-COOL?"¢ is added to the system, the engine coolant will require change sooner: at 50 000 km (30,000 miles) or 24 months.

1. Close the radiator drain cock.



2. If previously removed, install the engine block drain plugs.


When installing the drain plugs, use pipe sealer GM P/N 12346004.




Important: On vehicles equipped with the 3.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.




3. Fill the surge tank to the base of the filler neck.



4. Start the engine with the pressure cap off. Run the engine until the upper radiator hose starts to get hot.



5. If the coolant level in the surge tank is low, add the proper mix of coolant until the level reaches the full cold line.



Important: After servicing the cooling system, and if the vehicle is equipped with an intermittent low coolant light, an occasional low coolant light may be encountered during some extreme driving maneuvers. This complaint should be eliminated by removing the surge tank cap and adding coolant to a level just at or above the full cold line when the system is cold.




6. Install the cap onto the tank with hand tight pressure.

Recycling Procedure




Important: Dispose of used coolant in a proper fashion, such as in a used coolant holding tank. Never pour used coolant down the drain. Ethylene glycol antifreeze is a very toxic chemical. Disposing of ethylene glycol antifreeze into the sewer system is both illegal and ecologically unsound.



There is currently no approved method for recycling used DEX-COOL?"¢ coolant into new DEX-COOL?"¢ coolant. DEX-COOL?"¢ coolant can be recycled into new conventional coolant. Consult local listings for coolant recycling facilities in your area.

I've dealt with this vapor-lock issue in multiple ways. One was to put an aspirin in the thermostat to hold it open. When disolved it would work properly. But want it open for a bit so that coolant can flow.
The other was to squeeze the radiator hoses to push coolant and work air into radiator so it could come to top of radiator. Another is to simply run it till warms up, shut it down and ad coolant to the reservoir.

Suggests sign of internal leak. Check dipstick for engine oil to see if there is a sign of coolant mixed with engine oil. (Generally foaming of oil instead of amber or dark solid color) (Could even show level is high due to coolant adding to oil and raising level.)
If there is, it's a very serious problem.
One quick way to try a very inexpensive fix that's worked for me is a product called Barr's Leak. (It's worked twice for me on two cars.) Get the expensive "copper" version (looks like liquid copper) and add to your coolant system following manufacturer's instructions. Top off coolant and then drive car for a couple of full engine temperature sessions.
If coolant then no longer goes down, change engine oil draining out old coolant that may have contaminated it and refill with new filter.
Keep an eye on level after that to see if coolant level remains stable.
If coolant still goes down, a engine over haul or new engine may be needed.

Was the water added to the coolant reservoir or into the radiator? If the coolant reservoir it's a simple matter to unbolt it, drain it, reinstall and refill to proper level. If water was added to the radiator, it's best to drain the coolingg system and refill with the proper 50/50 mix of Dexcool. Water in the radiator will not hurt anything in the short term, but will not provide adequate protection.

What engine 2.2 or 2.4 ?
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Does the cooling fan come on ?
Notice: When adding coolant, it is important that you use GM Goodwrench DEX-COOL™ coolant. If coolant other than DEX-COOL™ is added to the system, the engine coolant will require change sooner: at 50 000 km (30,000 miles) or 24 months.
Close the radiator drain ****. Remove the drain hose.
If previously removed, install the engine block drain plugs.
When installing the drain plugs, use pipe sealer GM P/N 12346004.
Important: On vehicles equipped with the 2.4L engine, open the coolant air bleed valve. The coolant air bleed valve is located on the top of the thermostat bypass pipe/heater pipe assembly. Close the valve once a continuous stream of coolant is expelled from the valve.
Fill the surge tank to the base of the filler neck.
Start the engine with the pressure cap off. Let the engine run until the upper radiator hose starts to get hot.
If the coolant level in the surge tank is low, add the proper mix of coolant until the level reaches the full cold line.
Important: After servicing the cooling system, and if the vehicle is equipped with an intermittent low coolant light, an occasional low coolant light may be encountered during some extreme driving maneuvers. This complaint should be eliminated by removing the surge tank cap and adding coolant to a level just at or above the full cold line when the system is cold.
Install the cap onto the tank with hand tight pressure.

So you had it at several repair shop that can't find anything
or don't believ your loosing coolant

Sorry I can't guess I would need the car to check & test

Some major issue like a Head Gasket ??

have you noticed some coolant in your engine oil? it will make some bubbles/foam in your oil. If so, the engine head might be cracked and your coolant is mixing with your engine oil. That would explain the reason why your coolant goes down and your oil level goes up.

May just be low coolant level. Remove rad cap, or if none, coolant return bottle cap, and start engine and run heater while doing this. Now pay attention to coolant level and add as needed to top up the system. Let it run with cap off until rad fan comes on and off, 2 or 3 times and keep adding coolant if level goes down. Keep an eye on temperature gauge while doing this. It almost sounds like your coolant got low, or is low, and your heater has an airlock. Once coolant circulates back through heater and level is correct, see what happens.

If your coolant level is dropping, I would suggest that you take a good look at the water pump. That is a very common coolant leakage probelm area on your vehicle. I change 2-3 a week.
Hope this helps.