JoeHill

My friend has a 2006 CLK 350. 3.5 L 24V aluminum engine. Her mechanic says the intake manifold needs to be replaced, but didn't specify why. I think another person told her it's cracked. Is this a common problem with this engine? I'm more familiar with American V8's, and on those cars, intakes should never need to be replaced. They may need to be removed to install a new gasket, but you reuse the same intake again. An intake is (should be) one thing that never breaks or wears out, right? Is it true that some intakes today are made of plastic? Isn't plastic a poor choice of material for an intake manifold?

Rudeney

The intake manifold on modern MBZ engines is more complex than what you are used to. These devices have variable-length intake paths, so they are full of tubes and servos and flaps that articulate to adjust the length of the airflow paths. And yes, it is made of plastic, like so many parts nowadays. This is necessary to reduce weight in order to meet the conflicting government requirements of better fuel economy and improved safety standards.

Yes, plastic does break, but it's not a common problem for the manifold housing itself to crack on these engines. A slightly more common problem is that the plastic flaps and levers break. When that happens, you may be able to fix it with glue or "welding", but it really is best to replace the entire assembly. You don't want broken "parts" getting sucked into the throttle and engine.

JoeHill

Interesting. Thank you

mikischu

I had mine break late last year. It wasn't the aluminium part that broke, but one of the small black plastic levers on the outside of the thing.

Seems like such a small thing that broke, but the entire intake chunk of aluminium had to be replaced.

I think it might have broke when my engine was misfiring due to a back ignition coil.
Might have caused the engine to vibrate too much and snapped the plastic.