So last week i was running a bit late and had to give the car a bit of welly. Unfortunately i was only able to boot it for a couple of seconds because i got held up by a level crossing then again by a set of traffic light and then once again by a delivery truck that was taking up one side of the road (isn't it always the way). Anyhoo, when i stopped for the delivery truck a load of smoke come out on my exhaust and filled up the road, I then kept the revs low and by the time i was able to park up to have a look the smoke had stopped coming out. So while at idle i gave the car a good few revs and the smoke filled up not only the road but all the pavements as well. I limped the car home and have been keeping the revs below 2k and everything has been fine. I've been thinking the turbo seals must have gone and that i will need to get it rebuilt but today my mechanic told me to get it down to him so he could give it a test drive and also take the hose off the turbo to see how much play it had. Guess what...... No smoke and no play. After checking it out on the ramps...etc we took it out for a bit of a spin and pushed it to limits I've never done in the time I've had the car. but there still wasn't any smoke. When we got back we noticed that i was leaking coolant thought the housing on the side of the engine (part number 06a 121 133 j) So we replaced it. So my question is, what could have caused all that smoke last week ?