Am I burping the radiator correctly?

Just serviced my cars cooling system with a friend and per proper protocol, we proceeded to burp/bleed the system afterwards. When we were burping the radiator we did the following:

1.) opened the radiator cap on a cold engine and filled coolant to the top.

2.) put the heat on all the way and then turned on the car and waited about 20 minutes for the car to get to operating temperature and the fan to cycle on

3.) when the fan cycled on the coolant level dropped down and we topped it off again before the fan turned off

4.) after topping off, we waited another 5 minutes for the fan to cycle on again, and we saw bubbles coming out of the coolant while waiting as well.

5.) we kept repeating steps 3 and 4.

However, we did this for an hour and must have done 10 cycles of the fans turning on, sucking down the coolant and then topping it off. It is 4 am right now and we ran out of coolant so we had to just put the radiator cap on and call it a night. But the coolant level was still dropping and bubbles were still coming out during the last cycle the fans came on before we ran out of coolant and had to put the cap back on…which means there’s still air in the system…?

Someone correct me if I’m wrong, but all the air has been bled out of the radiator when the fan cycles on and the coolant level doesn’t drop? It seems off that we had to do so many cycles and used almost a gallon of coolant. Is it normal to have to do a lot of fan cycles/topping off when bleeding a radiator?

There are no coolant leaks anywhere by the way.

Check to see if there is a bleed screw for the coolant, one of my cars had it near the thermostat. I had to put my car on an incline to get the air to work its way to the screw.

If you are continually seeing bubbles you may have a head gasket breach

Tell us why you changed the coolant, what car, miles, maintenance history etc


To purge the cooling system of air, get the engine up to operating temperature.

While the engine idles, loosen the upper radiator hose clamp.

Take a small flat bladed screwdriver and slip it between the radiator hose and the hose neck on the radiator.

Allow the engine to idle until all the air is purged from the cooling system.

Remove the screwdriver and tighten the hose clamp.

Once the engine cools down, check the coolant level in the radiator.


I find it a lot easier to use something like this.

I’ve had a funnel like that for 20 years.

It doesn’t purge the cooling system of air.


I bled the air out using an airtight funnel and then turned off the car, removed the funnel and opened the bleed screw for a few seconds with the engine off. I saw a few bubbles come out of the bleed screw port and then I closed it and put the radiator cap back on. Did I do this correctly? Or are you supposed to open the bleed screw with the engine hot

How do you know how long to leave the screwdriver in and know for sure that all the air is gone? Do I just wait for the fan to cycle on and off a few times? Or is there a specific amount of time I should wait?

What I described is if the engine doesn’t have a bleed screw for the cooling system.

Open the bleed screw, add coolant until it comes out the bleed screw, close the bleed screw.

The engine doesn’t need to be running.


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Do I add coolant into the radiator or add it into the bleed screw port itself?

Do you have a funnel that will fit into the bleed screw port?

In the radiator!


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This is another dumb question, but if I open the radiator cap just to check the level, do I have to bleed it again since it’s being exposed to the outside air? Or do you only have to bleed if you’re actually adding or removing coolant?

If you remove coolant from the radiator and then refill it, the cooling system may need to be bled.

That’s why there’s a bleed screw.


First look under the hood at the relative level of the radiator cap, the thermostat housing, heater hoses and the heater core and consider if there are any locations where air would become trapped when the system is totally emptied. Just consider the heater core on many cars which is very near level with the radiator cap but one or both hoses that connect to it slope downward below the radiator cap and that causes an air trap to occur.

Every vehicle make and model is different and those with burping vents make life simpler but a few force you to go the extra mile to get the air out. Repeatedly filling, heating, cooling and topping off will eventually get the air out of many but often that process requires the vehicle to be parked on a steep incline to the front. Personally, I use Tester’s method of forcing a screw driver under the uppermost hose at the heater core with the engine cold and start the engine. As soon as coolant drips out that hose and the core are fully purged.

Do you realize that getting at some heater core hoses is almost impossible without removing other components?

And once you get there, it may require a special tool to remove the heater hose?

And once that happens, you have no control of the coolant flow?

Upper radiator hose is the easiest place to purge cooling system of air.


There are many ways to skin a cat @Tester. The Ford quick connects are so much trouble that I replaced the factory fitting with one that uses a hose clamp to connect the original hose after cutting off the quick connect. It seemed that I serviced dozens of Aerostar vans and they were the worst heater hoses to deal with. And then there is always the Prestone flush kit that once installed provides a permanently handy burp valve on the heater hose.

In my little corner of the world I have taken leave of factory fittings whenever it proved to benefit me if doing so had no negative effect to reliability or safety. And about those Prestone kits, I found a source for just the splice with a water hose connection and adapter and bought them by the dozen. With those fittings installed and the radiator filled and cap on tightly I connected 2psi shop air pressure to the radiator cap relief fitting and when coolant rose to the fitting the cap was installed and the system was purged of air.

Also those GM quick connects at the intake were never reconnected. Dorman had a hose nipple that was cheaper and more reliable than the quick connect.

I have a 2000 Chevrolet Silverado 1500 with those heater core fittings. I had to replace them, because the plastic had become brittle and worn-out, so my attempt to replace the heater hoses resulted in the fittings breaking off. And of course, I had to buy the special tool to remove the broken plastic fittings.

I purchased two of the Dorman replacement black plastic fittings. Looking at the metal stubs on the heater core, there was no possible way that I could have attached any type of hose without using the proper quick-connect adapters.

there are a great many options in repairing problems with quick connects which were/are a technological piece of junk contrived and used to eliminate the need to properly install hoses on the assembly line.