How to Change the Spark Plugs on a Mercedes M112 V6

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The M112 E24 V6 was the 2.4 litre V6 fitted to the C240, CLK240 and E240 in the years 1997-2000. The M112 has two spark plugs per cylinder and in the W202 it can look like quite a daunting task to get to them so I’m going to talk you through how to change them!

The tools you will need are a 10mm socket, a 10mm spark plug socket, a universal joint, various lengths of socket extension and a ratchet. You’ll also need the spark plugs of course! My recommendation is to get them from Euro Car Parts. You type in your registration and all the parts you need for the car will come up. Personally, I’d recommend the Bosch or NGK plugs. Today I will be using Bosch.

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Forst job under the engine bay is to remove the plastic cover. Simply lift the front with both hands and you will hear it pop away from its’ poppers at the rear and will left away.

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On both banks of the engine you will see these three black boxes. These are called coil packs. Two thick black cables come out of these and go down under the head to your spark plugs like so.

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The drivers side bank has exactly the same set up.

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Starting on the passenger side the easiest way to access the plugs is to remove the washer bottle. There is a small plastic nut at the top, simply remove that and then lift the whole thing out of the way.

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Now it’s time to remove the ignition lead from the end of the plug. Don’t grip the wire itself as they are SUPER expensive for these cars. instead grab the hard metal base and give it a pull. It will pop off the end of the plug. They can be a bit resistant and if they are just give them a wiggle and that will help to free them up.

Now to remove the plug. A spark plug has a long corrugation for the ignition lead to grip onto and to prevent flashover. Below that there’s a standard hexagonal head at the bottom of the ‘thing’ which leads to the thread that holds it into the engine.

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A spark plug socket has a rubber sheathe that goes over the corrugation then the actual socket grips onto the hexagonal bit like normal. Please note that spark plug sockets seem to be measured differently to a standard socket and seem to be measured by the diameter of the corrugation not the diameter of the hex. In the case of this vehicle, a 10mm spark plug socket is what is needed.

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Getting the spark plug in and out is the tricky bit. The universal joint is essential on the further back cylinders as they are difficult to access. On the forward most one on the passenger side bank it’s easier to go inside of the silver ducting rather than around it.

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The driver’s side is actually a little more accessible. The air filter housing has to come apart to get to them. It’s simply held on by 5 clips that flip up and then there is a jubilee clip on the top which unscrews and releases the whole top of the unit.

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Whilst that’s apart it’s also worth checking the air filter out. The air is drawn in from the bottom so the top of the filter will look mint but the bottom maybe full of dirt. Just pull it out, turn it over and have a look.

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All in all it’s not the hardest job to do but it does look a little intimidating, especially if you are used to working on little four cylinder engines.

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