Significant coolant loss in BMW – what is the reason and how to fix it?

BMW driver question

The following is a series of faults related to coolant and oil depletion in my BMW. Please let me know what could be the cause and how to fix it.

Description:

1. After replacing the thermostat, I noticed a slight loss of coolant, while there was no smear under the oil cap.
2. The clips were tightened tighter as the thermostat was damp, as if there was a slight leak on the connections to the thermostat.
3. Gradually, there was more and more fluid loss. The car was doing long distances of about 150 km per day on the highway.
4. The coolant and oil light came on several times.
5. I noticed a slight oil leak on the engine body.
6. After driving the car for three weeks, I added about 4 liters of coolant.
7. Yesterday, after a very short distance of 4 km, the low coolant light came on. There were coolant and oil stains under the engine near the thermostat. I added the fluid to the reservoir and drove the short distance of about 4 km home.
8. I noticed a different engine noise, as if air was being sucked in somewhere.
9. On the spot, I checked the coolant level, the level in the reservoir quickly got topped up and momentarily everything from the reservoir drained down somewhere, the engine body was wet from coolant and partly from oil. The area around the thermostat was also stained.

The problem affected a BMW 116i E87, but may also occur in other models.

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Response from BM Cars service

The symptoms described relate to two separate issues, oil leaks and coolant leaks. Adding 4 liters of fluid with a total cooling system capacity of 7.6 liters may indicate a very large leak or a lack of coolant loss control for an extended period.

In addition, after adding such a large amount of fluid, the entire cooling system should be vented. Lack of venting can cause the described effects. These are:

• a sharp increase in system pressure while the engine is running,
• a drop in the level below the acceptable level when the fluid filler cap is opened.

We suggest scheduling an appointment to check the cooling system for leaks, fix leaks and bleed the system. In addition, check the locations of any oil leaks that appear.

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