Rust in Coolant System, Heater Inoperative, Blows Cold Air (Flush Coolant System)

Some customers may comment that the heater is inoperative, blows cold air, the engine may exhibit an overheat condition or the coolant reservoir has rust in it.

Excessive aeration of the coolant under certain conditions may contribute to the formation of a rust-like material in the coolant system.

Flush the coolant system using the repair procedures below.

Parts and equipment required/suggested for this correction are listed below:

Important: It is recommended the vehicle be placed in a position where the following is available:

Caution: Do not remove the coolant recovery reservoir cap while the cooling system is hot. Serious personal injury may result. Only remove the cap from a cool engine.

1. Drain and properly dispose of the coolant. Refer to Draining and Filling Cooling System in the Service Manual.

Important: You can use various methods and equipment to flush the cooling system. If special equipment is used (such as a back flusher) follow the manufacturer's instructions. However, always remove the thermostat before flushing the system.

2. Remove the thermostat. Refer to Thermostat Replacement in the Service Manual.
3. Flush the entire cooling system with water only (including the radiator, pressurized coolant bottle and the heater core). Refer to Flushing in the Service Manual.
4. Back flush the engine and water pump with clean water until no debris is observed in the flushed water.
5. Drain and properly dispose of the coolant/water. Refer to Draining and Filling Cooling System in the Service Manual.
6. If the coolant recovery reservoir is stained, replace it with a new reservoir assemble, P/N 12528777. Refer to Coolant Recovery Replacement in the Service Manual. A new cap comes with the reservoir assemble.
7. If the coolant recovery reservoir is not stained, pressure test the reservoir cap and replace, if necessary, with P/N 25713160.
8. Install a new thermostat, P/N 12555290. Refer to Thermostat Replacement in the Service Manual.

Install a new front heater hose/valve assemble which includes the tee and the flow control assemble, P/N 10258504. Refer to Heater Inlet and Outlet Hoses in the Service Manual.

9. It is not necessary to replace the rear heater hoses attached to the heater core unless the hose condition warrants replacement.
10. Install a flow restrictor in the small hose between the coolant recovery reservoir and the throttle body. The restrictor kit includes the flow restrictor, clamps and the instructions (P/N DE-148 -- see Parts Information below).

Important: 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 mi) or 24 months.

11. Concentration:

The chemical inhibitors in DEX-COOL® are a critical part of protecting the cooling system. The inhibitors provide more than just freeze and boil protection, they are the necessary components for overall corrosion protection of the cooling system. A proper mix of 50/50 DEX-COOL® and water is essential. A 50/50 mix ensures that the proper amount of chemical inhibitors are in the coolant.

Notice: At low concentrations (less than 30% DEX-COOL® to water), these inhibitors may not be able to adequately provide corrosion protection and damage may occur to the cooling system components.

Important: Radiator drain and fills are a major contributor to improper coolant concentration. Drain and fills only remove about half of a cooling system's coolant. When the new coolant is added, it combines with the old coolant (with depleted chemical inhibitors) and the resulting mixture is considerably less than a 50/50 mix. For this reason, radiator drain and fills are no longer recommended as a means for a coolant change service.

Low coolant concentration can also result from topping off the cooling system with water and improper filling when system components are serviced. See table below for fluid capacity specifications.

Important: Because the cooling system was flushed with water and not all the water is removed from the coolant system, it is critical that you first fill the coolant system to one-half it's capacity with new 100% DEX-COOL® to maintain the proper concentration.

12. Continue to fill the coolant system with new 50/50 DEX-COOL® . Refer to Draining and Filling the Cooling System in the Service Manual. Also, refer to Corporate Bulletin #00-06-02-006 on engine coolant information.
13. Test the coolant concentration. Refer to Coolant Concentration Testing in the Service Manual.

Parts are currently available from GMSPO.

*Order the Restrictor Kit from:

Duratec Enterprises

P.O. Box 631

Simpsonville, SC 29681

To place orders by phone, call: 1-877-895-9234

For vehicles repaired under warranty, use: