Dear Car Talk:

My 1982 Mercedes 240D starts up faithfully without coaxing ... but with such a roar and shake that people wonder what, exactly, is going on under the hood.

It sounds like angry badgers fighting. Might it be bad motor mounts or something else that's the issue?

Thanks for your consideration. -- Denise



I think it might be your new hearing aids, Denise. It's probably been making those noises all along, but now you can finally hear that racket like everyone else. Try taking the hearing aid batteries out before starting the car.

Actually, given that this old diesel has been shaking and rattling for nearly 40 years, it could be anything and everything. You could certainly have multiple problems, Denise.

To me, angry badgers sounds like a bad belt. That makes a screaming, high-pitched noise that often starts when the car starts, and then goes away as the engine and belt warm up.

But you also mentioned a "roar." That could be something like a cracked exhaust manifold. If you have a crack in the manifold, that'll make a loud roaring sound when you first start the car. And then, as the hot exhaust heats up the manifold, the manifold expands and the crack closes up. That makes the noise go away. Until the next time you start the car.

Finally, you mention shaking. Let's assume this is above and beyond the normal diesel shaking. That could be caused by a cylinder that's not firing when you first start the car. If you have a bad injector, for instance, the car could start by running on only five of its six cylinders. That would cause it to shake like an unbalanced washing machine until the final cylinder kicked in.

I would say there's one thing that I'm absolutely certain you need, Denise.

A mechanic.

It's time to have this old heap looked over from stem to stern. And let the mechanic keep it overnight so he can hear what you hear when it starts in the morning.

At the very least, you want to make sure the car is still safe to drive and that nothing crucial is about to break or fall off. And if you determine that, then you can get a list of the other things that should be fixed. You may need everything we mentioned, and then some.

But only a thorough inspection will tell you that. Once you know the extent of the needed repairs, you can decide if you want to fix up this old soot bag, or skip over the internal combustion era entirely and buy yourself an electric car.

Actually, now that I think about it, that might be too much of a shock to your system, Denise. Going from shaking and blowing black soot to a silent, clean electric drivetrain might be too overwhelming to your senses.

So, if you do make the leap, make sure you get a massaging and vibrating seat and some cheap incense to help you work through the transition.