I OWN A 03 slk 200k with 38,000 miles, I have notice that if the car is stood for more than 2 days without being started when i do start it there is a rattle for a slit second from the top end, if used every day no problem.I know this must be the oil draining down but is this normal or is there a problem with this car because i have 2 other makes of cars which can be stood for a week or more and never get this problem.the oil which is in the engine is 0W-40W as used by MB dealer, would it be better to use 5W-40W.

 

Seems like you have the correct diagnosis. 0w-40 has a better viscosity range than 5w-40 so stick with the recommended.

What brand of oil is being used? It should be recorded in your Service book. MB dealers use many brands but the MB recommendation is Mobil 1. Very expensive but maybe try that. It just could make the difference if the noise offends you.

Stuart