Blue smoke it does it when it starts up and when im driven

Blue smoke is not good!! Piston rings are bad or valves. On a Mercedes it will cost you more than the car is worth at this point. Unless you have a sentimental attachment to the car and really really want to keep it., I would get rid of it. 123,000 mile is a great life for a 1989.

blue smoke is burning oil
I gather that you let the engine idle and when you give it rpms that there is a cloud of blue smoke
if that is the case it indicates that the valve stem seals are hard /failed and when the engine is at idle ( 15" mercury vacuum in manifold) the oil around the valves is sucked past the stem seals and into the combustion chamber
AS you have restricted use of the machine (every 3 weeks ) it is not a great problem as when you are on the road it is not happening (Only at idle )
It is repairable without removing the head if you find an accredited service shop that has experience in the procedure.

all cars smoke for about a hour driven hard, if you get oil all over.
smoke from where? tail pipe end, or exhaust manifold, where?
?
2.5L? V6, like mine?

Burning oil. Could be a couple of things. Possible your valve guide seals are warn out. If its blue smoke mostly when you first start the car, its likely valve guide seals. If its continuously smoking blue, its more than likely a broken or warn out piston ring. If its just every so slightly blue in tent, it might be worth a try to replace your PCV valve first. When the PCV valve gets completely gummed up, the pressure inside your valve covers has no way to vent other than forcing its way through the valves into the cylinders often times taking oil with it. Since PCV's usually only run out about $10 its worth a shot. Other wise, you've got a decent overhaul ahead of you for either piston rings or valve seals...on a 12 year old car most folks would either choose to scrap it, or live with the blue smoke while monitoring oil levels and watching for fouled plugs. Hope that helps and good luck!!

if you have done the gasket on valve cover then not tightend enough
valve rubbers will make smoke blue also the piston rings

valve seals are going. when car sits excess oil gets past the valve seals then when you staRT up it burns the oil off then runs fine and no more blue smoke. It is fine to run like that had the same in a dodge caravan 1996 6cyl. ran another 100 000 km. and still ran fine got rid of it for other reasons.

have you driven it at least 100 miles since repair?, the oil residue builds up inside the exhaust and burns off very slowly from the previous failed turbo seal.

It sounds like you may need valve seals.
The oil sits in the head after the engine is cut off and leaks around the seals into the cylinder.
When you start the engine it burns the oil and sends the smoke out of the tailpipes.
It does not hurt anything much if it is not to bad.

Blue smoke is caused by engine oil entering the cylinder area and being burned along with the fuel air mixture. As with the white smoke, just a small drop of oil leaking into the cylinder can produce blue smoke out the tailpipe. Blue smoke is more likely in older or higher mileage vehicles than newer cars with fewer miles.

This could mean a cracked head or bad gasket....It costly

Hi, thanks for your reply! My car is SORN and has not been driven for some time. Because I don't want the battery to go flat, I regularly go out and run the engine for a while. The smoke is black(ish) and smelly. I haven't driven through any large puddles. The water in the footwell isn't a large amount but I have a rubberback mat on top of the orginal capet and that is quite wet (as is the carpet underneath). Although my car is due a service, it has always been well maintained and services done when they are due (except this time because I'm off road)! Because it hasn't been driven, I can't imagine where the water has come from. I did wonder if it has something to do with the air conditioning. Sometimes when the air conditioning is run, you get a bit of water that runs out from under the car, this I think is normal, as I've seen it before on other cars. I did wonder if the smoke was anything to do with not having driven the car or having only a small amount of fuel in the tank most of the time?

Many thanks