My 5.4 overheats after 1st warmed up, starts blowing cold air out the heater, then I put it in neutral, shut it off, turn it back on and every things fine. I tested the coolant tank for exhaust etc. and everything came out negative. I had the intake gasket replaced in January and the overheating stopped, but soon after so did my heat. I was told to flush out the heater core to see if that helped and that leads me to where I am now. I read another thread that suggested this could be a head gasket, but the isn't any oil in the antifreeze, antifreeze in the oil, or antifreeze out the exhaust like before with the intake gasket. I just don't understand how draining the antifreeze can cause issues to pop up. I would think it would have purged all of the air out of the system by now so I don't know if that is an issue. Is there a good way to bleed the air out after flushing the coolant system?

 

I've posted this about a gazillion times now, but.... go to the parts store and purchase a flush & fill kit for less than $15. Its a plastic T fitting with 2 barbed ends and one threaded end. You splice it in-line on one of your heater hoses with a couple hose clamps. You can then remove your coolant reservoir cap and hook up a water hose to the fitting and flush the system. You'll also be filling it from its highest point where air will tend to collect. Its much easier to get all the air out of the system. I've ran them on all my vehicles for 15 years now with no issues.

 

So since I've already refilled the coolant I should be able to use the T to purge the air out at the top?

 

Yessir!

 

Thanks I'll give it a shot after work. From what I've seen on these sites it looks like a common problem.

 

Well I put the T in and the neighbor and I got all of the air out of the system and has worked great until yesterday. It got to the normal operating temp and I had no heat. After about 10 minutes it started overheating so I shut it off. Did that 2 more times and then it started blowing heat and the temp went back to normal. Could I be getting bad thermostats that just last a couple of months or could there be some kind of other problem. I did the gas test in the coolant reservoir and came back negative and the coolant is still nice and green so I don't believe that is an issue. Still has the original water pump. This all started after a coolant flush back in November 2013. It had ran fine with no issues for me over the last 14 years until then. Any other ideas?

 

Three possibilities I can think of. T-stat is failing as you suggested. Water pump impeller is damaged. Or there is still a small amount of air trapped in the system. Your not getting any coolant in your passenger floorboard or smelling antifreeze in the cab are you? If so, heater core leak. As far as the T-stat, did you go with a fail safe model? And make sure the cap on the T fitting is good and tight. Could suck in air from there.

 

There has to be Air in the system. The problem seems too erratic to be a Clog or part failure.

Pull out the T-stat, fill it all back up with water and see what it does. It should stay on the cold side but if it overheats your problem is somewhere else.

Does your water pump shaft have any play in it at all? Usually, you can either see coolant dripping or you can hear it going out.

 

There isn't any coolant or smell in the cab so I don't believe it's the core. The t-stat is a murray brand from O'reillys. I thought about swapping that out for a Motorcraft because my bother-in-law said the off brands they used at the Chrysler dealership were junk and sometimes replaced the 2-3 times before they got one that worked. If there is air it would cause the t-stat to not open and the coolant would get pressurized enough to blow out the reservoir until the air was gone? I don't think the pump shaft is going. There isn't any coolant leaking or any noise from it. Is there any way to test the pump to see if the impeller is ok without pulling the pump? The Illinois weather sucks right now and I don't have a heated garage.

 

Kinda thinking out loud here...
First,get it pressure tested to rule any leaks.There are places that will test it for free
Is it possible that when you flushed,you broke loose a chunk of something that is still floating around in the system?
Or could something have been introduced into the cooling system when you had the intake gasket replaced?
I'm not sure if that's even possible,but I've seen some pretty heavy corrosion in some vehicles,and if a chunk of that stuff was to break loose I imagine it could cause some issues.