from what you have explained i would get a compression test done first.
the colour of the smoke tells me it is burning engine oil so the maybe some damage to the valve gear or cylinder head or piston liners/rings.
did you hear abnormal noise leading up to this point?
is the engine miss firing?
check the exhaust tail pipe is the oil present?
what is the mileage on this engine?
is the coolant sytem heating up as normal?
My answers are as follows:
1. A compression test showed low pressure on cylinder 2
2. Sometimes the very light blue smoke is dense smelling mostly of petrol; at other times it is slight, but still smelling of petrol. The smell of petrol pervades both the engien compartment and the interior of the car.
3. A sort of 'rattle' noise is now there continuously but was not in evidence leading up to the first morning when it suddenly happened (when parked up the night before it had been running perectly!)
What I omitted to say before was that after the injectors were 'flushed thru' during a major service, the engine worked perfectly for about 5 days when, whilst idling, it suddenly went 'lumpy' and the smell of petrol returned. It has remained like that. My tame garage suggested it may be a sticking valve but they were not familiar with the W124 Mercedes engine.
3. Yes, the engine is misfiring - 'lumpy'
4. There does not appear to be oil in the exhaust. As I say, the overwhelming smell in the exhaust is of neat petrol.
6. This is an interesting question. Prior to the incident, I noticed that the temperature gauge on the instrument panel was barely registering so I assumed the 'thermometer' unit in the top of the block had failed and asked for a new one to be fitted. It was, but there is still barely a reading.
Does this help?
thanks for the info.
it would be helpful if you could tell me what the reading was on number 2?
Unfortunately I have no idea as I was not present when the garage did it. I only know it was 'low'. The other 3 were to spec.
from the info on the coolant side it seems as though the thermostat is stuck open and not allowing the coolant to warm up this can cause a slight over fuelling but not to the degree that you can smell fuel like you have described.
the compression readings if just low then maybe the injector on number 2 is faulty and firing exccessive fuel into the cylinder and to much to be combusted this can wash the bore and cause oil to come past the rings and be burnt hence the blue smoke.
if the compression reading was exceptionaly low the yes there has been some damage caused and will nee the head removing for further investigation.
i have an idea get your tame garge to swap injectors 2 and 3 around to see if the missfire moves to cylinder 3 the think about replacing the injector.
i will leave this question open for you to reply back with the results of this test.
OK. This will take a couple of days to organise. I call back then.
look forward to it.