BMW Coupes and Sedans 1970-1988 Repair Guide

Cooling System

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BMW recommends that the coolant be changed every 2 years. Collect your used coolant in a clean pan, do not allow any other fluids to mix with it, and return it to a recycling facility or shop. Do not drain the coolant on the ground or pour it into a sewer.

FLUID RECOMMENDATIONS



BMW recommends that an ethylene glycol based antifreeze coolant be used. Stay with a name brand that is compatible with aluminum and is nitrate and amino free. The coolant should be a 50/50 mix to achieve protection to -35°F. (-37°C.). Any concentration in excess of 50/50 will actually reduce the effectiveness of the fluid as a heat transfer medium.

LEVEL CHECK



See Figures 1, 2, 3 and 4

It is recommended that you check the coolant level every time you stop for fuel. If the engine is hot, let it cool for a few minutes before checking the coolant.

Check the freezing as well as the boilover protection rates at least once a year, preferably just before the winter and/or the summer. This can be done with an antifreeze tester (many service stations will have one on hand and will probably check it for you, if not, they are available at most automotive parts stores). Maintain a protection rating of at least -35°F (-37°C) to prevent engine damage as a result of freezing and to assure the proper engine operating temperature.

In addition to testing the coolant protection level, the cooling system should also be pressure tested at least once a year. To perform a pressure test, a coolant pressure tester is required. Although available at most automotive parts stores, this tool is fairly expensive; therefore, you may wish to have this service completed by a mechanic.

A pressure test runs an artificially high pressure level though the entire cooling system. This pressure level will show whether the cooling system can withstand this level, which it should, and if there are any weak hoses or components which may need replacement.



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Fig. Fig. 1: Checking the cooling system freezing and boiling points with an antifreeze tester



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Fig. Fig. 2: An example of a coolant reservoir



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Fig. Fig. 3: Remove the cap slowly to relieve any system pressure



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Fig. Fig. 4: Add coolant to the reservoir up to the MAX line

DRAIN AND REFILL



See Figures 5,6,7 and 8

The cooling system should be drained, thoroughly flushed and then refilled at least every 30,000 miles (48,000 km). This should be done with the engine cold.

  1. Remove the radiator cap, if equipped.
  2.  


CAUTION
Make sure the system is cool before removing the cap!

  1. Turn the heater control to WARM .
  2.  
  3. Loosen the radiator end clamp on the lower radiator hose, and pull the hose off the radiator connector.
  4.  



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Fig. Fig. 5: Loosen the plastic draincock at the base of the radiator



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Fig. Fig. 6: Carefully remove the draincock. The coolant may be hot



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Fig. Fig. 7: Allow the coolant to drain into a suitable container



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Fig. Fig. 8: A funnel may be used to control coolant spillage

  1. Remove the 19mm plug from the right rear of the engine block.
  2.  
  3. Allow the coolant to drain completely before installing the plug and radiator hose.
  4.  
  5. To refill the system, first replace the drain plug and reconnect the radiator hose and clamp it.
  6.  
  7. On 6-cylinder engines, loosen the bleeder screw on the thermostat housing. On all other engines, make sure the heater control is still in the WARM position.
  8.  
  9. Fill the cooling system with a 50/50 mixture of antifreeze and distilled water and then replace the filler cap, turning it to the second stop. Start the engine and run it at 2,500 rpm until normal operating temperature is reached, and then stop it. If equipped with a 6-cylinder engine, watch for water coming out at the bleed point, then close the bleeder screw. On other engines, when the engine is cool, check the coolant level in the radiator, or expansion tank and add antifreeze if needed.
  10.  
  11. Start the engine after a wait of at least 1 minute and then run it at 4,000 rpm for 30 seconds. Release the throttle and make sure heat comes from the heater at idle speed. Then, shut off the engine again.
  12.  

SYSTEM BLEEDING



See Figure 9

The cooling system must be bled to remove air from the coolant passages. If the system is not bled, hot spots can form leading to overheating and engine damage.

To bleed the cooling system, proceed as follows:

  1. Fill the radiator and reservoir, if equipped, with coolant.
  2.  
  3. Run the engine at normal operating temperature.
  4.  
  5. Set the heater controls to WARM .
  6.  
  7. Bring the engine idle up to 2000 RPM.
  8.  
  9. Unscrew the bleeder bolt at the thermostat housing until the escaping coolant is free of air bubbles.
  10.  



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Fig. Fig. 9: Unscrew the bleeder bolt to allow trapped air to escape

  1. After the system has been bled, tighten the bleeder bolt and check that the coolant level is correct.
  2.  

Integral Expansion Tank Systems

These systems have the expansion tank as part of the radiator assembly. It is the vertically mounted, translucent tank on the side of the radiator.

  1. With the expansion tank filled with coolant mix, run the engine to operating temperature. Set the heater controls to WARM and engine speed to fast idle.
  2.  
  3. Loosen the radiator mounted bleeder screw. Allow coolant to run out of the bleeder until a solid stream of coolant and no air is coming out. Keep the expansion tank full during this step. Tighten the bleeder screw.
  4.  
  5. Turn off the engine, but keep the ignition switch in the ON position. On vehicles with a thermostat housing bleeder screw, open the screw and allow coolant to run out of the bleeder until a solid stream of coolant and no air is coming out. Keep the expansion tank full during this step. Tighten the bleeder screw to 4.5-7.0 ft lbs. (6-10 Nm).
  6.  
  7. Start the engine and run at 2500 rpm. The coolant level will drop to the COLD mark on the expansion tank or close to it, indicating that residual air has been purged from the system.
  8.  
  9. Install the expansion tank cap.
  10.  

Remote Expansion Tank Systems
EXCEPT M5 MODELS
  1. With the expansion tank filled with coolant mix, run the engine to operating temperature. Set the heater controls to WARM and engine speed to fast idle.
  2.  
  3. Loosen the thermostat housing mounted bleeder screw. Allow coolant to run out of the bleeder until a solid stream of coolant and no air is coming out. Do not allow the expansion tank to run dry during this step. Tighten the bleeder screw to 4.5-7.0 ft lbs. (6-10 Nm).
  4.  
  5. Fill the expansion tank to the COLD mark, then install the tank cap.
  6.  

M5 MODELS
  1. Fill the expansion tank to the MAX marking.
  2.  
  3. Start the engine, then press the side and window defroster button on the climate control panel.
  4.  
  5. Loosen the cooling system bleeder valve located near the remote positive battery connection. Allow any air to escape, then tighten the valve.
  6.  
  7. Refill the expansion tank to the MAX mark and run the engine at 2500 rpm.
  8.  
  9. When the level in the expansion tank steadies itself at the MAX mark, replace the fill cap.
  10.  
  11. If the expansion tank is equipped with an air fill valve, use a tire pump to pressurize the cooling system at the fill valve on the expansion tank to 7 psi (0.5 bar).
  12.  


WARNING
If the system is not pressurized, engine damage will occur. The system is designed to be precisely pressurized. If the system cannot be pressurized at the moment, avoid driving the vehicle, or limit the engine speed to 3000 rpm or less until the first possible opportunity to restore pressure.

  1. If the expansion tank is not equipped with an air fill valve, check the present coolant level, then allow the engine to cool for at least 6 hours and recheck the level. The coolant level should be between the COLD and MAX marks with the engine warm, and at the COLD mark when cold.
  2.  
  3. If the level has to be adjusted, remove the cap and add the required amount of coolant. If the amount was in excess of 1.1 quart (1 liter) repeat the bleeding procedure.
  4.  

FLUSHING AND CLEANING THE SYSTEM



With the use of electrically actuated heater valves and bi-zone heater cores, it is not easy or advisable to cut hoses to mount a flushing tee. Drain the system, add clear water, bleed the system and run the engine to flush the system of old coolant. Drain the system, add fresh coolant and bleed the system. This will get rid of most of the old coolant and keep the cooling system in good shape. It is important to change the coolant on a regular basis, every 2 years, as this will prevent corrosion from building up and creating the need for cleaning the cooling system.

RADIATOR CAP INSPECTION



See Figure 10

Allow the engine to cool sufficiently before attempting to remove the radiator cap. Use a rag to cover the cap, then remove by pressing down and turning counterclockwise to the first stop. If any hissing is noted (indicating the release of pressure), wait until the hissing stops completely, then press down again and turn counterclockwise until the cap can be removed.



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Fig. Fig. 10: Radiator with traditional radiator cap-2002 model


CAUTION
DO NOT attempt to remove the radiator cap while the engine is hot. Severe personal injury from steam burns can result.

Check the condition of the radiator cap gasket and seal inside of the cap. The radiator cap is designed to seal the cooling system under normal operating conditions which allows the build up of a certain amount of pressure (this pressure rating is stamped or printed on the cap). The pressure in the system raises the boiling point of the coolant to help prevent overheating. If the radiator cap does not seal, the boiling point of the coolant is lowered and overheating will occur. If the cap must be replaced, purchase the new cap according to the pressure rating which is specified for your vehicle.

Prior to installing the radiator cap, inspect and clean the filler neck. If you are reusing the old cap, clean it thoroughly with clear water. After turning the cap on, make sure the arrows align with the overflow hose.

 
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