The bleed plug on my top radiator hose had developed a leak so I have replaced with a new hose, where the bleed plug is place on the top of the T, and I have also replaced the thermostat for good measure. After first attempt to bleed the system (incorrect method) all seemed fine, but after about an hourof driving heat went cold and engine temp shot up fast. I imediatley pulled over and shut down, and had coolant escaping through overflow line. Let cool down and filled back up and got it home with no problem. After reading though numerous posts on overheating and bleeding methods, i bleeded the system out by removing the bleed plug and filling system with the expansion tank elevated untill coolant poured out of the bleed plug in a steady stream, refit bleed screw and topped off tank. Still had the same result off after about an hour of driving having the heat blow cold and engine temp shoot up. I live in Northern Virginia and found Rover Technicians who used to work at dealerships but now are putting together there own shop, and they come out to you to give you afree diagnonis. I called them up to see if they could do a pressure test on my system to see if I had a bad head gasket. Tech came over, but did not have a pressure tester with him, but proceeded todiagnose my truck. After about an hour or so with him looking over the car, and having his diagnonis computer plugged into the truck he said it had no head gasket problems, and that most likely I just did not get all of the air out of my system. He bleed the system while he was there and was confident that all of the air would have been out of the system. On my way to work today I had the same issue with the heater suddenly blowing cold and engine temp rising. Any ideas what may be wrong here?

 

With the heater blowing cold, that is the typical trapped air problem caused by a coolant leak or a system that has not been totally bled.
First, never ever turn off your engine when it over heats. Pull over, turn on the heater to high and let the engine idle till the engine cools. By not doing this you are allowing the overheated engine to get even hotter since the is no flow of coolant to cool it down. Doing this can cause your engine to drop a sleeve and then you will be in the market for a new engine.
Get the coolant system pressure tested before you loose your engine, it is as simple as that. How many miles on the engine, how many times has it been overheated? It may already be too late, and the only way to tell is to pull the heads and look for warpage of the heads, cracks, failed head gaskets and dropped sleeves.

 

I agree w/ disco Mike, but also check your t-stat. Could be as simple as having gotten a bad one, I knowa few people this has happened to over the years.

 

I have it in the shop now getting the system pressure tested. It has 110,000 on it.