Have a 2000 s500 the engine makes a loud clacking noise.but when in gear its louder and will over heat if i drive on freeway more thana few miles. Sounds like there's no oil but it does.

Normally tiney rattley noises are just heat shields that have come loose check under the bonnet and under the car for loose heat shields also the heat shield around the cat can corode and come lose hopevthis helps ivan

Check for other loose heat shields.
The shield you removed would allow more noise to enter the cabin too.

sounds like a c.v. axle is bad.

soiunds like a wrist pin but more like a cracked piston,

Certainly have the a scan of your computer done to find the fault codes for the check engine light. This will help you proceed.

As far as the oil light, Usually indicates low oil. make sure your oil level is correct.

you have a rod knocking in the engine

What do you mean by loud... Loud where??? If noise is from engine, make sure that the mechanical fan clutch is not "locked" (it's supposed to freewheel when cold... if it does not, it will "roar" when driving.

If it was your cranshaft making that kind of noise.your motor would have frozen up already.it seems more like a tranny problem than an engine problem. Take it to a good mechanic. It sounds like your tranny is about to go.

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If the clacking noise gets louder when turning its the drive joints at the front wheels