Oil Mixing With Coolant? Here’s What to Do

Resolving the Issue of Oil Mixing With Coolant in a Mercedes-Benz CLA W117 with M270 Engine

Vehicle: Mercedes-Benz CLA W117 with M270
Complaint: Oil Mixing With Coolant

Introduction

In the world of automotive maintenance, one of the more alarming issues that can arise is the mixing of oil with coolant. This problem not only jeopardizes the performance of the engine but can also lead to severe damage if not addressed promptly. In this case study, we’ll explore a real-world scenario involving a Mercedes-Benz CLA W117 equipped with the M270 Engine. This vehicle was brought into the workshop with the complaint of Oil Mixing With Coolant, a situation that had persisted despite the recent replacement of the oil cooler—twice. We’ll walk through the diagnostic process, identify the root cause, and outline the steps taken to resolve this issue.

Diagnosing the Issue

Upon the vehicle’s arrival, the initial step was to conduct a thorough diagnostic check. The primary focus was on the cooling system data, which revealed that the engine temperature was consistently higher than the specified range. This abnormality raised concerns about the cooling system’s effectiveness and indicated that there might be underlying issues beyond the oil cooler itself.

Visual Inspection:
A close examination of the reservoir tank revealed clear signs of oil mixing with the coolant. The fluid exhibited the characteristic milky appearance that occurs when oil contaminates the coolant, confirming the owner’s complaint. The customer also disclosed that the vehicle had experienced an overheating incident prior to the current situation. This information was crucial, as it suggested that the overheating may have compromised the integrity of the cooling system components.

Identifying the Root Cause

To pinpoint the root cause of Oil Mixing With Coolant, the investigation focused on several key components:

1. Engine Cooler and Gearbox Cooler:
   Both the engine oil cooler and the gearbox oil cooler were removed and inspected. It was found that both coolers had developed leaks, which allowed oil to seep into the coolant system.
2. Thermostat Valve and Coolant Pump:
   The thermostat valve and coolant pump were crucial elements to check. The cooling system relies on these components to maintain the engine’s optimal temperature. The examination revealed that the diaphragm-type valve, operated by vacuum within the water pump, was malfunctioning. This failure was likely causing the engine to operate at higher-than-normal temperatures.
3. Auxiliary Pump and Radiator:
   Further checks included the auxiliary pump and radiator, both of which play a vital role in regulating engine temperature. Any blockages or malfunctions in these parts could contribute to overheating, exacerbating the issue of Oil Mixing With Coolant.
4. Water Pump Valve Mechanisms:
   The Mercedes-Benz M270 engine features a water pump with two open-close valve mechanisms on either side of the engine. These valves are essential for proper coolant flow. The investigation revealed that one of these valves was not operating correctly, which contributed to the temperature rise and subsequent oil mixing with the coolant.

Problem Solving

With the root cause identified, the next step was to address the malfunctioning components and restore the cooling system to its optimal condition:

1. System Flush:
The radiator and cooling system were thoroughly flushed to remove any contaminated coolant and residue. This step was critical to ensure that no oil remnants would remain in the system, which could lead to future issues.

2. Replacement of Defective Parts:
The defective components, including the thermostat valve, coolant pump, and the malfunctioning valve in the water pump, were replaced with OEM (Original Equipment Manufacturer) parts. These high-quality replacements were essential to restore the system’s integrity.

3. Use of Recommended Coolant:
The system was refilled with the manufacturer-recommended coolant, which is designed to operate within the specific temperature range required by the Mercedes-Benz CLA W117. The use of ordinary water as a coolant in the past was identified as a contributing factor to the overheating issue, so switching to the proper coolant was crucial.

4. Testing and Verification:
After the repairs were completed, the cooling system was tested under various driving conditions to ensure it was operating within the optimal temperature range. The functioning of the thermostat valve and cooling fan were also verified to confirm that the system was now performing correctly.

Conclusion

Oil Mixing With Coolant is a serious issue that can lead to significant engine damage if not addressed promptly. In the case of the Mercedes-Benz CLA W117 with the M270 engine, the root cause was traced to a combination of overheating and component failure within the cooling system. By conducting a thorough diagnostic process, replacing the defective parts, and ensuring the system was properly flushed and refilled, the issue was successfully resolved.

This case study underscores the importance of maintaining the cooling system and using the correct coolant to prevent such issues from occurring. Regular maintenance and prompt attention to warning signs like overheating can save vehicle owners from costly repairs and prolong the life of their engines.

How to remove oil from coolant?

Removing oil from coolant is crucial to restore your vehicle’s cooling system to proper working order and prevent engine damage. Here’s a step-by-step guide on how to remove oil from coolant:

1. Identify the Source of the Leak

• Inspect the Engine Components: Before attempting to remove oil from the coolant, it’s essential to identify and fix the root cause. Common sources include a blown head gasket, a faulty oil cooler, or a cracked engine block.
• Repair the Leak: Address the underlying issue by repairing or replacing the defective component. This prevents further contamination of the coolant.

2. Drain the Contaminated Coolant

• Locate the Radiator Drain Plug: Position a large drain pan under the radiator drain plug. Unscrew the plug and allow the contaminated coolant to drain completely.
• Drain the Engine Block: Some vehicles have drain plugs on the engine block to ensure all the coolant is removed. Open these plugs if available.

3. Flush the Cooling System

• Use a Coolant Flush Solution: Purchase a commercial coolant flush solution designed to remove oil and other contaminants. Fill the cooling system with the flush solution, following the manufacturer’s instructions.
• Run the Engine: Start the engine and let it run for the time specified by the flush solution manufacturer, usually 10-15 minutes. This will circulate the solution throughout the cooling system, helping to break down and remove the oil.
• Drain the Flush Solution: After running the engine, drain the flush solution as you did with the coolant.

4. Rinse with Distilled Water

• Refill with Distilled Water: Fill the system with distilled water and run the engine again for a few minutes to rinse out any remaining contaminants.
• Drain the System Again: Drain the distilled water from the system.

5. Repeat if Necessary

• Check for Residual Oil: Inspect the drained water for signs of oil. If there’s still oil present, repeat the flushing and rinsing process until the drained water is clear.

6. Refill with Fresh Coolant

• Choose the Correct Coolant: Once the system is clean, refill it with the manufacturer-recommended coolant. Using the proper coolant ensures optimal performance and protects the engine from overheating.
• Bleed the Cooling System: To avoid air pockets, bleed the system according to your vehicle’s manual. This ensures the coolant circulates properly.

7. Dispose of Contaminated Fluids Properly

• Follow Local Regulations: Dispose of the contaminated coolant and flush solution according to local environmental regulations, as these fluids can be hazardous.

8. Monitor the System

• Check for Leaks: After refilling the system, monitor it for leaks and ensure the oil contamination does not recur. If you notice any issues, revisit the source of the leak and confirm the repair was effective.

Removing oil from the coolant is essential for maintaining engine health. By following these steps, you can effectively cleanse your cooling system and prevent further damage to your vehicle.