Technical Strong burning smell and white smoke from the front - mechanics can't find anything wrong!

[NorthCR94]

I have a FIAT DOBLO 16V TREKKING MAXI MTJTII and it has been producing a burning smell for a while, and a month ago it had 2.7l of oil replaced as there was nothing in the compartment, even though there was no signs of leaks anywhere. A few weeks later it was empty again, with no signs of leaks anywhere. It went into the garage yesterday, and the mechanics were stumped as they couldn't find any sign of a problem. This morning it started producing the burning rubbery smell stronger than ever and white smoke was coming from the front grille for a few minutes before dissipating along with the burning smell. Again, the garage couldn't find a fault, they told me everything was dry inside and the exhaust was clean. I am befuddled, and the garage told me they have never seen anything like it!
Has anyone experienced anything similar?
The stop/start has also stopped working for a while if that means anything?

Thanks in advance!

 

[Zardo]

I don't think oil will produce white smoke. Check your radiator and coolant levels. Check the adblue reservoir, too.