In my recent case. I had to wait until the van cooled down, then the bonnet opened first pull on the lever as if nothing was ever wrong. I degreased it all of old gunky grease and used silicone spray and some graphite powder to lube the mechanism and cable as best I could. Works fine now.
The long version:
I had a minor coolant leak on one of the plastic fittings, about 1l every 250km. I did not have time to fix it because we were going on holiday in the van the next day. So I thought I'd be cunning and just stop and top it up every 250km on our 1200km round trip. You can see where this is going...
All was well stopping and topping up until I was about 200km from home returning on a hot day. The bonnet simply would not open. One person, two people, nada. The lever was very hard to pull, and it seemed like the sheath of the cable was deforming due to heat-soaking during a long trip in high ambient. I just nursed it home keeping a close eye on ECT and OIL temps. Made it home just fine and in the morning the bonnet opened perfectly.