I went to a dealer and I got 2007 Cadillac DTS I drove the car around for a test drive. The car seems fine. I got the car home and the car started to overheat. The dealer will not help me in anyway I have changed the water pump. I have changed the thermostat. I have flushed the radiator. I have done a compression test. It seem to be no leaks and I’ve even got a cap for the reservoir overflow and it’s still overheating, the car only overheats when I drive it. It does not overheat when I let it idle.
Running as opposed to idle, the fans working shouldn't matter as much. Because at idle you need the radiator fans more than you need them going down the road with fresh air being pushed through the radiator (without the A/C on) as opposed to idle (when you're standing still)
So start with hooking up a cheap scanner and in "Live Data" observe the ECT temp.
Here, I'd start with a combustion gas leak test because really small leaks aren't apparent at idle but when you "give it the beans" they can overheat the cooling system.
Scotty has a video on this but in your case, have a helper hold the rpms to 2,500 to 3,000 rpms while you perform the test.
This could be anything from a partially clogged radiator, or a restriction in the cooling system, to a tiny combustion gas leak (which a combustion gas leak test will only show above 2,500 rpms)
