Running straight water in the summer wont cause a problem. Water holds more BTU's of heat than does antifreeze, so it does a more effective job of carrying heat to the radiator, but you need the antifreeze for its corrosion inhibitors, water pump lubricant, and other additives.
Feel the upper radiator hose when the engine is warmed up. That hose should be too hot to hold onto for very long. If it is, coolant is flowing and there will be no air pockets in the engine. If the hose is cool, you may need to bleed the air out and / or fill the system. If an air pocket forms under the thermostat, that won't open and let coolant flow to the radiator. Thermostats have to be hit with hot liquid to open. Hot air won't do it. The coolant could still circulate through the hater core and be cooled by it, but if it gets too hot, you will hear the gurgling as coolant is pushed into the reservoir. Also, if the system is not kept under fifteen pounds of pressure by the radiator cap, the temperature can be expected to go higher than the boiling point of water, so the water in the coolant will boil and gurgle. GM runs a lot of their engines as high as 222 degrees. For each pound of pressure, the boiling point of water goes up three degrees. That is why we need the system to stay under pressure.
Dash gauges are notoriously inaccurate. They are only good to let you see when something is not normal or what you are used to seeing. It is better to use a scanner to view live data to see the exact temperature the coolant is at. If the engine really is too hot, given the age of the truck, start by looking at the cooling fins on the radiator. If they crumble like a rotten chocolate chip cookie, they won't be able to give up the heat to the surrounding air.
Check the front of the radiator or air conditioner condenser for a butterfly collection. If it is bad enough, that will block air flow. Check for the rubber weather seal under the front edge of the hood, and for anything missing from the front that leaves a hole that air can flow through. Either of those things will allow air to bypass the radiator. A lot of people think the radiator will cool better if they remove the shroud, but that is backward. The shroud forces the fan to pull cool air through the radiator and it prevents heated air from going back around and coming through the radiator again.
Feel all areas of the radiator. If there is a cool spot, that area is plugged. You should hear the fan change the sound it makes when the thermostatic clutch kicks in. Stop the engine when its hot, then feel how hard it is to turn the fan by hand. If it spins easily, have your mechanic do additional tests to see if it's working properly.
Keep in mind some gurgling after you stop the engine is to be expected. The engine is still giving up a lot of heat to the coolant, but it is not being carried away to the radiator. That coolant will be expanding and getting forced into the reservoir. The upper radiator hose should be hard at this time. If you can squeeze it easily, there isn't any pressure in the system, and that must be corrected before looking for other causes that may not exist.
Wednesday, June 29th, 2016 AT 10:41 PM