Hi, I've the same issue. Cooper S 5year old 77600km, 2 litre petrol. Changed oil & white smoke on start up only lasting about 10 to 15 seconds, mostly morning time & nothing throughout the day, this is going on a couple of months now & have had it with 4 different mechanics who could find nothing. About 4 weeks ago the smoke has stopped & no smoke on start. Not losing coolant or oil & car in top form when driving. Had to wait 6 weeks for appointment with Mini garage, so decided to keep the appointment out of interest to see would they find something. Two days later they can't find any fault so they posted on a forum today & said based on the responses they received recommend replacing the gasket cover at a cost of over 1k. They showed me the note they had posted, but it didn't sound like the issue I was having, it said car blowing blue smoke & trace of oil in turbo, so I mentioned the smoke was white & asked had they found oil in the turbo to which they replied no, so I find it bizarre they can make a recommendation to carry out work with no guarantee it will fix the issue. At the moment, no smoke & car driving fine. Any advice would be appreciated.
Neither my 2018 JCW or my 2023 S smoke upon start up. But a couple of my other cars would emit a bit of oil smoke at cold start. I first noticed this when I was in the process of buying a new car and upon engine start prior to the test drive the engine smoked a bit. Techs I talked to told me they see this often with used cars on the lot and even new cars. They went on to say as long as the smoking was brief and was not accompanied by a CEL or untoward engine behavior they paid it no mind.
I'll add to if the engine doesn't smoke at hot start or at other times.
As is my habit with my cars is I seek to avoid short trips. And run the right oil and change it on a bit of shorter schedule than the factory calls for.
As oil gathers miles it becomes contaminated. One side effect of this is it is more prone to vaporization. The engine air/oil separator (AOS) is intended to remove the oil vapor but these are not 100% effective. As a result some vapor flows through the separator and when it reaches the intake manifold the oil vapor being heavier can't make the sharp turn. Rather the vapor hits the opposite wall of the intake and there regains its liquid form.
If the engine is allowed to run long enough this bit of oil will be pulled into the engine and burned. Because the amount of oil is small and the engine/converter is hot there is no smoke.
But if the engine is shut off this oil can drain down and collect on top of a closed intake valve or flow through an open intake valve and enter the cylinder.
Upon the next engine start smoking is observed.
In spite of my avoidance of short trips and changing the oil at 5K miles vs 6K or 10K or even 15K (as called for by the factory) as the miles on the oil approached 5K I'd see -- just a time or two -- smoking upon engine start. This was a sign the oil was at its replace by miles.
Of course there can be other explanations. Engine overfilled with oil. A bad PCV or a bad AOS. (With one car over 317K miles I had to replace its AOS 3 times. It was a wear item.) Less common is bad rings, bad valve stem seals, or bad turbo seals. But with bad rings, bad valve stem seals, or bad turbo seals smoking would almost certainly show up at other times.
That your car's engine stopped smoking suggests the problem is one of usage. Short trips perhaps. Or you overfilled the engine with oil. Not sure if the wrong oil could account for the smoking but it is important to use the right oil and of course fill up the engine but don't overfill it.
