Apart from the obvious loss of s heating system and demister are there any negatives to getting rid of heat exchangers?

No you don't need them if you don't need heat!

Fresh air fan to clear a foggy windshield.

Not something used all that often in disco bay, i presume?

No heat in my car for nine years. Don't need it, don't miss it. Although I still have the fresh air fan to defog the windshield.
Cheers, Elliot

I should have guessed that is what it is called in New Zealand!

I suppose I was just concerned that without them there might be more heat getting around the sump and therefore raise the oil temparature. But the I guess there is enough air blowing past that area so as not to cause the problem???