I've fixed this specific fault on at least 3 S4+ 928s. I only had to diagnose it once, although that took a long time as it is just not apparent that anything is amiss when the car is stationary.

For any 928 that overheats or just gets warmer whilst on the move versus stayting cool at slow speeds with the AC on in high ambient temps it has to be THE 1st check. Given the efficiency of the 928 cooling system when it is working correctly if you live in a temperate climate you could have this problem and never actually know that your 928 was supposed to run a lot cooler than it does.

 

Brent ,
I had trouble with overheating (190 degree) in less that 40 mph air flow with ambient above 75 and felt it was an airflow issue as the raptor sc I put on from carl had 2 small 8 inch fans to replace the 2 stock fans......I found out I also had waterpump problems as I drove the car to finally get the build from GB and when he pulled the engine the impeller was grinding on the block...so I also had coolant flow issue (40K on older lasso pump.not a rebuild)
talk to you later
andy