Hello i replaced my head on my 91 2.3 ...everything went well new head, head bolts, timing belt kit, water pump,.and thermostat. So I gets all this in, all goes well starts up no problem. The issue I had was once it got up to temperature. Water would spew out of radiator fearsly, like it was overheating. So I thought my brand new thermostat was defective. So back again no thermostat still same problem then the engine seem like it had no power at idle put my foot down hardly any revs. Thought car might be blocked. So out comes the spark plugs on exhaust side which are easy to get at. Spark plugs looked good. So cost i disconnect coil packs. Then took 60amp fuse to fuel pump relay to be save. I did compression check all cylinders 165. So back in they go. So I tried the tunnel check in the radiator, roped up with water. And disconnected the heater core hose to possibly bleed the air in system. But still no luck. So I topped up resoivoir and rad. And put the cap on, started it and waited for maybe 10 mins but seem to be fine this time so took her down the street and up a hill came back and seem to be fine so went for longer drive. Stop checked no hissing or popping in rad. Now it's perfect no boiling or air in the system. Baffles me there must have been a big air pocket somewhere now it sorted it self out. Now have to do thermostat again and put some fresh coolant. i guess this must have to be a closed system for it to bleed itself? If anyone songs to give me any info has to what might have happened head this is my first time working on 2.3 Ford engine...cheers

 

Welcome to the forum

Yes, you probably had air in the head, taking off heater hoses at firewall when filling helps let the air out from behind closed thermostat.

Thermostat should have a "jiggle valve", small hole with a metal pin in it that jiggles, hence the name, lol.
This should be placed at the 12:00 position when installing thermostat, it is there to let air out when filling but also in general if air does get into system.

Yes, your system is self purging of air.
With engine running water pump will circulate coolant thru the engine and heater hoses, any air will be at the top of the system, too much air can form an "air dam", water pump can't push it out of the way, so you do need to try and get as much air out as possible.

When thermostat opens any remaining air will move to the top of the radiator and stay there.

As the coolant heats up it expands in volume, that's where the pressure in the system comes from.
Radiator caps have TWO Valves, larger valve is usually rated for 16psi pressure
At 17psi larger valve opens and sends hot coolant over to the overflow tank.
If there was any air in the radiator it would come out first, and bubble up to top of overflow tank, this is why overflow hose is connected to the BOTTOM of the overflow tank, and why the overflow tank is not sealed, air needs to get out.
So self purging
When engine is shut down coolant cools off and shrinks in volume
If any air or coolant was sent over to the overflow tank then pressure in the radiator will drop below 0psi to -1psi, and the smaller valve in the center of rad cap will be pulled open, this will suck coolant in from the bottom of overflow tank back into the radiator.
If you ever had a vehicle that got collapsed upper rad hose after it was cold than means the smaller valve in rad cap is bad or overflow hose or tank is blocked, system has -1psi so hoses collapse from outside pressure.

So to check if your system is working correctly, open rad cap when engine is cold, it should be topped up to the very very top, no air at all.
If there is air then check overflow hose for leaks and overflow tanks bottom for blockages.

If there is even a small leak in the cooling system then rad caps smaller valve can't do its job, at -1psi air will be sucked in from the small leak, not coolant from the overflow tank, because air is easier to move than the coolant.


Not sure why the engine ran poorly.