Overheating Defender 90 converted 200TDI

If anyone could throw any light on this I would be delighted as it has me stumped.

Conversion was done about 3 yrs ago and later fitted with an uprated turbo and intercooler. Performance was greatly improved and was all fine until it was taken off road. The rad got clogged and it overheated. After that despite cleaning the rad and then replacing it, new thermostat, hoses, flushing, new waterpump, kenlowe fan, back to viscous fan it overheats at anything over 60 on the motorway. Local garages have tinkered and all they can come up with is a cracked block. I don't see any signs of that however, is it a possibility and how can that cause the overheating problem? - it doesn't lose coolant incidently.

Thanks

is rad hot allover its surface ,if it isnt replace it

above 60mph suggests insufficient flow, remove the stat and see if the problem is still there to at least eliminate the stat as being faulty (new ones occasionally are), its only a 2 minute job

Cheers Steve

Thanks for the replies, yes the rad is hot all over, the reason it was replaced is that it burst after my daughter in law ignored the overheating and drove it with the temp gauge in the red zone. I don't know whether that is an indication of the problem I've never had a radiator burst before. I have thought about airflow and ensured the shroud is in place and nothing obstructing the rad. I suspect that the larger turbo is heating up the intercooler rad too much which is in front of the rad causing it suck in hot air from the intercooler.