Subject pretty much says it all. There is no radiator cap and the thermostat housing doesn't have a bleeder valve. Periodically, the van will run hot, and no heat out of the heater. After a minute or two it returns to normal and I have heat again. I have replaced the thermostat twice to no avail.
The system 'flows' through a coolant tank on the wheel well. This tank is NOT full, it has an air space. Fluid comes in and goes out as coolant circulates. Bubbles in the air 'should' collect at the top of the tank.
The problem is there can be some air pockets at the 'top' of the engine. My Intrepid has a 'bleeder' valve, similar to a brake bleed valve, on the top of the thermostat housing. Even with that, there can be air pockets.
Actually, the system is pretty neat when it works. And usually it will 'self bleed' as long as there's not other problems. When I refill after a flush, I squeeze the hoses until I can stop bubbling, but even then, the next few times I drive the thing I have to 'top it off' as the works itself into the tank.
Could try to run it until hot, release pressure by loosening the coolant tank cap. Do it a few times, may help get air out. Be careful of overspill, though, out of the tank, it bubbles out rather fast.
The subject says everything except the year of the vehicle, If it is an older model just loosen the heater hose at the intake and let the air go out that way as you fill. If you replaced 2 thermostats and the problem is still there...you have another problem. Is the coolant going low and you don't see any leaks?
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