Chevrolet Repair: overheatin 98 C1500, radiator flush, radiator cap

Question
i just gave my 1998 C1500 a radiator flush and clean. i used to only use the green coolant, i had no overheating problems before. The guy at the store recommended to use the red coolant on GM vehicles. So i flushed the radiator and the engine and poured in 50/50 mix of coolant and clean water. Afterwards i went and checked for leaks and all of that stuff, every thing was ok. So i went for a test drive and i drove it for 5mi. and when i came to a stop the temp gauge rose up to 260. i drove it home catiously and slow when i checked under the hood all of the coolant was pourin out of the reservoir. My guess is that the coolant could be causing this problem, but GM recommends to use the red. just to be sure what could be the cause of this problem?

Thank you for your time.


Answer
Using Dexcool coolant will not cause overheating unless the mixture between coolant and water is not mixed correctly. You stated that you put in a 50/50 mix.

I would replace the thermostat. It possibly stuck in the closed position.

Also refill the coolant and run it without the cap until all the air is bled from the system.

It's not a bad idea to replace the radiator cap too.