Can’t seem to get all air out of rad

[88sclb350]

Trying to bleed my cooling system and I bought one of those funnels that goes on rad cap but it was junk and just leaked everywhere the “Chevrolet” cap didn’t fit well.

So I’ve been trying to just bleed it with the rad cap off, truck running, heat on high and blower on high, revving it up. That gets air out but I’ve done that twice each for 20 minutes and it seems like I can’t get all the air especially after I rev it every time I get big bubbles.

So am I sucking air somewhere or what can do I do get the air out better?

 

[Drunkcanuk]

Trying to bleed my cooling system and I bought one of those funnels that goes on rad cap but it was junk and just leaked everywhere the “Chevrolet” cap didn’t fit well.

So I’ve been trying to just bleed it with the rad cap off, truck running, heat on high and blower on high, revving it up. That gets air out but I’ve done that twice each for 20 minutes and it seems like I can’t get all the air especially after I rev it every time I get big bubbles.

So am I sucking air somewhere or what can do I do get the air out better?

Elevate the front end on jack stands?

 

[RichLo]

Dont worry too much about it, fill up the overflow reservoir and drive it like normal. It will eventually burp out any remaining air and the overflow will automatically refill it with heat/cool cycles.

 

[TechNova]

fill the radiator, wait a few minutes to let it gravity burp, add a little more, Repeat once more then put the cap on.
Fill the overflow to the line, start it up and drive it or run it outside if you need to check for leaks. Check the overflow after a few days.
It is not a braking system, you will always have air in the cooling system.

 

[GMCTruck]

Keep an eye on your temperature gauge though while you are driving around.

 

[Schurkey]

Trying to bleed my cooling system

WHY? Did you do cooling system service recently? New water pump? Had the intake manifold off? Heater core work? Something else?

If you haven't opened-up the cooling system, "air" in the system is a sign of compression leakage into the cooling system (head gasket, cracked castings) or a coolant leak.

So I’ve been trying to just bleed it with the rad cap off, truck running, heat on high and blower on high, revving it up. That gets air out but I’ve done that twice each for 20 minutes and it seems like I can’t get all the air especially after I rev it every time I get big bubbles.

So am I sucking air somewhere or what can do I do get the air out better?

Not "sucking air", but pressurizing with combustion gasses would be my guess.

There's nothing in a GMT400 gasoline truck (I don't know about the diesels) that traps air. You run the engine at fast idle or higher, the thermostat opens, the air is immediately in the radiator. You top-off the coolant including the overflow bottle, put the rad cap on, shut the hood, and you're done.

If there's more to it than that, something is wrong.

 

[thx1138v2]

You could have a leak between manifold water port and the exterior of the engine. I had that problem once and the water/coolant never showed up on the driveway. The leak was above the water pump where the manifold had a leak to the outside of the head but there was a catchment cast into the top of the water pump and when I turned the engine off when hot the water evaporated from there into the air so none of it hit the driveway.

Go to the auto parts store and get a loaner water system tester. Wait until the following morning when the engine has cooled off, attach the tester, and pump it up as the instructions say. The come back in half an hour to an hour and a half and check the pressure gauge. If it has dropped significantly you have a water leak somewhere. You'll need to start pulling parts off until you find it. Mine was between the manifold and the head on the front, passenger side water port. It was just a worn manifold gasket. It wasn't that hard to fix but it did take some time. I couldn't see it because it was behind the A/C compressor mounting bracket. Once I had the compressor loose and pushed out of the way I could see a puddle of coolant just sitting the water pump casting.

 

[Scooterwrench]

A little trick I have used for years is to drill a 3/32" hole in the thermostat flange. It creates an air bleed without affecting the temp calibration of the thermostat. A 1/8" hole will drop the calibration 5 degrees.

 

[Benny B]

I just replaced my radiator. The No Spill Funnel did not fit my GM radiator, so in a hurry I decided to burp the system the old fashion way, I forgot to lift the front end up on the jack though. So I was burping the system on level ground. I filled the radiator and coolant reservoir, let gravity burp it, filled the radiator again, ran it with the cap off, revving the motor and squeezing the hoses. I didn't do this very long though, then I put the cap on the radiator and drove it like half a mile. My temp gauge got up to 230/235. I got scared and turned around back to my house, (so drove 1 mile total, probably 4 minutes). When I was turning back into my driveway the thermostat opened and the temp gauge went down to below 200.

I shut off the motor, the coolant sounded like it was bubbling, so right at the boiling point....yikes. I added probably half a gallon or 3/4 of a gallon of coolant to get it topped back off. The system now is running at 200 degrees and holds temp at 200 degrees, but man that was SCARY and now I'm wondering if I hurt the motor by running up to 235 degrees for 4 or 5 minutes due to an air pocket.

I should have waited and gotten a different no spill funnel.

What do you guys think? Should I buy a head gasket test kit to see if I have exhaust gases in my coolant?

1995 GMC 1500 5.7L TBI, 2wd, 5 Speed

 

[Sean Buick 76]

No worries that wouldn’t hurt the engine. I simply run them with the rad cap off till the thermostat opens and it burps out the top of the rad. Top up the rad and done. No need to elevate or rev the engine or squeeze hoses lol.

If your head gasket is shot you will see air bubbling out through the rad with the cap off.