Originally Posted by Dodgevity

A radiator pressure tester should not be used while the engine is running. The cap of the pressure tester is basically a solid plug and will not allow coolant to have a path to the overflow, so the system will bust for sure if you do this.... like a sealed pressure cooker.

I'm having trouble understanding "back flowing in the resi"....

If the radiator is full while cold and you run the engine, the coolant heats up, expands and overflows into the tank. Now as it cools, it the coolant contracts and should back flow back into the radiator due to the system falling below atmospheric pressure. If it doesn't flow back into the radiator for whatever reason, then the overflow stays full. If the overflow stays full, the level in your rad should drop when cold.

Now why it's busting radiators, well I wouldn't blame three busted radiators on them being cheap. Obviously there is an issue. With system cold, take off the rad cap and start the vehicle. Does the coolant move? It wouldn't hurt to pressure test the system. Also you can use a block tester to test the HG. Both these items can be rented for free from the auto parts stores (once you return them), so you've got nothing to lose in trying them.

I got you beat on mileage