BURNING SMELL WHEN DRIVING UPHILL

Hi everyone.
I have Corsa 1.3CDTI 2004 and have problem with burning smell, hope someone can help me.
During my last drive everything was fine untill app. a half a minute uphill bit of road when i have noticed burning smell (like burning brakes smell) and engine temperature rising from 80deg (as usually on dual carrigeway). When i have reached a top of the hill everything came back to normal, no smell and temperature back to 80deg.
Anyone have any clue what can it be?

Thanks