Top-end rattle
Q My 2004 Mercedes SLK 230 R170 with the M111.983 engine has just 46,000 miles, so doesn’t do a lot each year. It has had some dealer servicing early in its life, but the last owner had not had it serviced and it got regular use when I first bought it, but I did not notice any issues with the engine. I later changed the oil and filter myself using Comma fullysynthetic 5W-40 and a motor factor filter, which was when I first noticed an odd noise.
The noise is a rattle which seems to come from the top-end, camshaft, followers or variable timing mechanism. It only happens when the engine is really cold after standing for a few days and until the oil pressure builds up, after which it is very quiet. It does not rattle through all rev ranges or if stopped for a short time. I have noticed that if I start the engine as soon as it is cold, there is no rattle, and if allowed to run for a few seconds it can then can be left for a few days and when started there is no noise. I suspect the oil is draining away completely from somewhere when the engine is hot and the rattle will then be present until the oil level has risen again.
Thinking it might have something to do with the oil or filter, I went to see our local independent Mercedes repairer for advice and got some Mobil fully-synthetic
5W-40 and an OE filter. Even after changing these, the noise was still there.
I have looked on online Mercedes forums and the same noise is mentioned by other owners, but they have no definitive answer as to what it is or whether it is safe to leave it alone. There is also mention of a technical bulletin covering the noise, but I have not been able get hold of it. Should I try changing the oil and filter again and would a different oil or viscosity help?
John Holliday
A You will appreciate that, without hearing the noise, I can only make general observations.
The oil you are using is correct for your vehicle and I would not advise using any alternative grade. Castrol do recommend their Edge 0W-40 A3/B4, but I don’t believe this will make any difference.
As you suspect, the noise is very likely to be valve followers that have drained down. Providing it only happens at start-up and is very quick to disappear, it should not give you cause for concern. The problem could also be a timing chain rattle, but given the low mileage of your car this is unlikely.
I have discovered a Mercedes document (No SM05.20-P-0002A) that makes reference to replacing the camshaft positioner solenoid on engines 111.983 in model 170.449, but does not specify the reason for the replacement. The replacement parts are listed as: A111 051 01 77 05 solenoid, A111 997 01 86 plug, A271 150 27 33 05 adapter cable and A002 997 24 90 cable tie. However, if the camshaft positioner solenoid was faulty on your car, I would expect the EML to be illuminated.