NOTE: For safety, make sure the engine has cooled down before proceeding with these steps.
1. Gather the necessary tools and parts:
- Replacement Thermostat with Gasket (specific to BMW 528I model)
- 9/16" Wrench or Socket
- Slot Head or Flat Head Screwdriver
- Phillips Head Screwdriver
- Coolant (BMW-Approved Anti-freeze or equivalent)
- Funnel
2. Drain coolant:
- Locate the drain plug on the bottom of the radiator. Place a container underneath the plug.
- Unscrew the drain plug using the 9/16" wrench to allow coolant to drain. Wait until the draining is complete.
3. Locate the thermostat housing:
- Open the hood of the vehicle and locate the engine. The thermostat housing is usually situated on the front or side of the engine, connected to the upper radiator hose.
4. Remove the upper radiator hose:
- Identify the upper radiator hose which connects the radiator to the thermostat housing.
- Loosen the hose clamp with the appropriate tool, then gently pry the hose off the thermostat housing. Set aside the old hose and make sure to keep any residual coolant for disposal.
5. Remove the old thermostat:
- Use either the slot head screwdriver or the Phillips head screwdriver (depending on the type of screws used) to remove the bolts securing the thermostat housing to the engine. This may require a bit of force.
- Once the bolts are removed, carefully remove the thermostat housing. Be cautious as some residual coolant may leak out.
6. Replace the thermostat:
- Place the new thermostat into the housing. Make sure the positioning matches the old thermostat.
- Install the gasket over the thermostat to ensure a proper seal.
7. Reinstall the thermostat housing:
- Place the thermostat housing back onto the engine, ensuring proper alignment.
- Secure the housing with the bolts you removed earlier and firmly tighten them.
8. Reattach the upper radiator hose:
- Reinstall the upper radiator hose onto the thermostat housing and secure the hose clamp.
9. Refill the coolant:
- Open the radiator cap and slowly add the proper coolant using a funnel.
- BMW-approved anti-freeze or equivalent coolant is always recommended.
- Fill until the coolant level is between the "Min" and "Max" marks on the reservoir.
10. Bleed the cooling system:
- Start the engine and allow it to reach its normal operating temperature.
- Turn on the heater and set it to the highest temperature setting.
- Allow the engine to run for a few minutes while monitoring the coolant level.
- If the coolant level drops, add more until the level stabilizes.
11. Test the thermostat:
- Let the engine cool down slightly and then start it again.
- Observe the temperature gauge while the engine warms up.
- The temperature should rise steadily until the thermostat opens, and the gauge should indicate a steady reading.
By following these steps, you can successfully replace the thermostat on your 1998 BMW 528I. Keep in mind that if you're not confident in your mechanical abilities, it's best to seek assistance from a professional.
