I searched around on the web for a while looking for lycoming and continental engines ambient operating temp limits to compare, but came up empty handed. All that is usually mentioned in the bulletins and manuals I found is that the oil must be suitable for the ambient temperature, and the mixture adjusted in such a way as to make the engine run cooler (ie, richer not leaner)
It would be interesting to see a correlation of failure vs. ambient air temp on failed engines. I do realise that the ambient temp on the ground is different than in the air, but not all that different at pattern height.
The only conclusion i can come to, (edit: without seeing a failure vs airtemp graph) is if you live in the northern half of Australia, or indeed most of Australia, don't operate a jab after 8am or before 6pm.
Any LAMEs or l2-l4s want to comment?