Need to get the scoop on draining and replacing the coolant for a C5. The labels on the coolant tank say there is a special procedure to follow in the shop manual. I assume it's to purge any air out of the system. I did a look around and search on this site, but doesn't seem to be covered anywhere. Anyone up on this?

Thanks in advance
LBJ

 

yeah ttt

 

Here you go! Please note that there are TWO procedures listed here, one for refilling and one for a complete flush. These are from the '99 shop manual, but I believe it can be applied to all years.


Draining and Filling Cooling System
Caution

With a pressurized cooling system, the coolant temperature in the radiator can be considerably higher than the boiling point of the solution at atmospheric pressure. Removal of the surge tank cap, while the cooling system is hot and under high pressure, causes the solution to boil instantaneously with explosive force. This will cause the solution to spew out over the engine, the fenders, and the person removing the cap. Serious bodily injury may result.

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 cooling system seal tabs, or similar compounds, unless otherwise instructed. The use of cooling system seal tabs, or similar compounds, may restrict coolant flow through the passages of the cooling system or the engine components. Restricted coolant flow may cause engine overheating and/or damage to the cooling system or the engine components/assembly.

Drain and Fill Procedure
Important
If the procedure below is not followed a low or high coolant level condition and/or vehicle damage could result.
1. Park the vehicle on a level surface.
2. Follow the steps below to remove the radiator surge tank fill cap:
* Slowly rotate the cap counterclockwise1/4 turn and then stop. Do not press down..
* Allow any residual pressure, indicated by a hissing sound, to be relieved.
* After all hissing stops, continue turning counterclockwise to remove the cap.
* To tighten the cap, use hand tight pressure only.
3. Open the radiator drain fowl.
4. Allow the system to drain completely.
5. Inspect the engine coolant:
o Discolored -- follow the flush procedure below.
o Normal in appearance -- Continue with the next step.
6. Close the radiator drain fowl.

Important
When filling the cooling system use a 50 to 60 percent concentration with DEX-COOL® coolant.
7. Fill the system through the surge tank opening.
8. Fill half the capacity of the system with 100 percent DEX-COOL® coolant.
9. Slowly add clean drinkable water to the system until the level reaches to the base of the neck.
10. Start the engine.
11. Idle engine for 1 minute.
12. Install surge tank cap.
13. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
14. Shut off the engine.
15. Refer to step 3 above to remove the surge tank cap.
16. Start the engine.
17. Idle engine for 1 minute and fill surge tank to 1/2 inch above COLD FULL mark on the radiator surge tank.
18. Install the surge tank cap.
19. Cycle the RPM, idle to 3000 in 30 second intervals until engine coolant reaches 99°C (210°F).
20. Shut off the engine.
21. Top off coolant as necessary, 1/2 inch above FULL COLD mark on the radiator surge tank.
22. Rinse away any excess coolant from the engine and the compartment.
23. Inspect the concentration of the coolant.

Flush Procedure
Important

Do not use a chemical flush.
1. Block the drive wheels.
2. Place the transmission in Park or Neutral.
3. Engage the parking brake.
4. Run the engine until the thermostat opens.
5. Stop the engine.
6. Follow the drain and fill procedure using only clean drinkable water repeat if necessary until the fluid is nearly colorless. Refer to the drain and fill procedure.
7. Fill the cooling system. Refer to the drain and fill procedure.

 

I followed the above procedures, BUT I used a 50 / 50 mixture of Dex-cool / distilled water instead of "Fill half the capacity of the system with 100 percent DEX-COOL® coolant.", then I added a 50 /50 mixture.

I have had problems with leaks and overheating when using 100% coolant in the past on other cars before adding water. Besides capacities vary, why not use 50 / 50 and get concentration correct.