Those Jag V8s are pretty tough. I've seen them get well over 245F and be fine after the problem was repaired. I thought for sure one of mine had blown a head gasket after the thermostat malfunctioned. Had it towed in and had the thermostat replaced under warranty, and it has been fine since. If it had been a rover V8, the HGs would have been toast for sure, and quite possibly the block.