Why does my Mercedes-Benz make a bubbling noise from the coolant reservoir when the engine is hot?

Steve Mowat

Steve Mowat

Steve Mowat, Owner of Avantgarde Automotive, began as a BMW apprentice in 1997, then excelled at McLaren and Mercedes-Benz. In 2009, he founded his business.

A symphony of engineering, the heart of a Mercedes-Benz engine should purr like a contented cat. However, what do you do when it sounds like a boiling kettle instead? Let’s put on our detective hats.

The Heart of Excellence – Mercedes Engine Bay

The Culprit: Bubbling Coolant – A Common Miscreant

One might say the coolant reservoir is the social gathering spot for bubbles. It’s all a jolly good show until the orchestra turns discordant.

  • Heat and Pressure: When the coolant can’t dissipate heat effectively, it may boil and cause bubbling noises. C’est la vie for the Mercedes E-Class W213 (2016-2021), where a water pump not functioning optimally has often been the culprit.
  • Air in the System: The sophisticated coolant system is no place for a freeloading air pocket. Sometimes the air doesn’t bleed out properly, notably in the Mercedes-Benz GLA Class (2014-2019).

Tip: Remove the air by elevating the front of the car (use a reliable car ramp). Leave the cap off and run the engine until the fan kicks in. Top up with coolant as necessary.

Tools and Parts: Arm Yourself, Brave Mechanic

Ready your tools! For this quest, you’ll need a coolant tester, a reliable car ramp, a socket set, and a service manual (invaluable advice, chaps).

  • Coolant Tester: Measures the boiling point of the coolant.
  • Reliable Car Ramp: For proper elevation during the battle against air pockets.
  • Socket Set: For accessing the coolant reservoir and related components.
  • Service Manual: Grab the Haynes Manual. It’s like a treasure map for your Mercedes.

A Swift Gander at the Cap & Hose

When Sherlock Holmes investigates, he leaves no stone unturned.

  • The Cap: The coolant reservoir cap might just be a double agent. If it’s not holding pressure properly, it can cause the coolant to boil prematurely. A replacement is needed! (Part number: A0005010615).
  • The Hose: Your Mercedes might have a pinhole leak in the coolant hose. Grab a torch and inspect the hose for any leaks or damage.

Tip: If you need to replace the hose, the part number for the Mercedes C-Class W205 is A2055010625.

DIY or Avantgarde?

If DIY is not your cup of tea, consider Mercedes-Benz ServiceCare for a seamless coolant system repair. However, if you fancy a bit of mechanical adventure, be sure to document your valiant efforts.

When the Symphony Gets Too Boisterous: The Radiator Fan

Check the radiator fan, squire! If it’s not spinning with the zeal of Sir Lancelot, it might be a failing fan motor or a dodgy relay.

  • Fan Motor: Test the voltage. If it’s not within spec, you’ll need a replacement (Part number: A0999062400 for the 2020 Mercedes GLE-Class).
  • Relay: Swap it with a known good one and check the fan.

Tip: Keep an eye on the temperature gauge! If it’s rising faster than the British Pound, turn off the engine posthaste.

Your Noble Steed Deserves the Best

Your Mercedes is an exquisite piece of art and deserves the utmost care. The coolant reservoir shouldn’t be a cauldron of chaos. Ensure that the symphony under the bonnet is as harmonious as Elgar’s Enigma Variations. However, the tips and advice shared here are just that. The author holds no responsibility for any incorrect or out-of-date information.

Feeling the need for a knight in shining armour? Mercedes Repairs in Bristol might just be your Holy Grail.

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