"Burping" air from radiator

Okay does anyone know a trick on how to burp air that is trapped in your cooling system. Don't know for a fact that this is what's going on, but I'm running out of ideas. I have a brand new radiator (AFCO), new water pump,new thermostat and new water pump. All of this on a new 350/330hp crate motor. Sitting at an idle the motor runs at 180 degrees with the fan kicking on and off like its supposed to. But when driving the temp will run normal for awhile then go up to around 225-240. It won't stay there long but I don't think that this is normal. It reminds me of when a thermostat sticks, but I've put 2 new ones in.(180 degree) I've even put a new temp gauge and sending unit in. I'm running a 16 lb cap. Any ideas?

 

Do you have a electric or mechanical fan? HRP

 

I have had to burp air from several sbc's. I did it by parking the car pointed up my somewhat steep driveway. Used a big floor jack and lifted the front of the car as high as it would go. Removed the radiator cap, started the engine, and watched the engine self-burp itself. You will see and hear it happen, if there was an air pocket in the cooling system. Trapped air will travel upward and out.

 

run car with rad cap off, watch for level to go down when themostat opens and keep filling it, youll see bubbles working there way out. you can also jack front of car up will running, this will also help air work out.

 

Agreed, lift the front end up.

If you have access to it try an "Air Lift". This tool puts your cooling system under vacuum then fills your cooling system that way.

 

2100cfm electric

 

What he said ^

 

I'll try the "nose up" trick.

 

They make a wide mouth funnel with the bottom attached to a radiator cap. When the coolant gets hot it will back up into the funnel until the thermostat opens. When the thermostat opens, the coolant level will drop releasing trapped air.

I had the same problem using a mechanical gauge. When I switch to an electric gauge, the problem went away. Same with mechanical oil pressure gauge. It took a long time to read pressure. I switch to an electric and it was instantaneous.

 

I never heard of the nose up but have let the radiators self burp with the cap off,,maybe that stops it form spitting up. HRP

 

High temps at highway spend is usually a radiator or airflow problem. Electric fans don't run at highway speeds.

 

You say electric fans don't run at highway speeds?

 

Getting access to the highest part of the system is the key.



On an O/T vehicle, I had to put one of these on a heater core line in order to completely bleed the cooling system.

 

I have heard it said that heating up at idle is usually related to a fan that is insufficient, and heating up at speed is related to a radiator with insufficient capacity.

That is, provided that the basics are covered...Timing, advance working properly, fuel mixture good...etc.

 

The top radiator tank is actually the highest point of the cooling system on my car.

 

Drill a 1/8" hole in the flat part of one of your old thermostats and reinstall it.

 

Does the vehicle puke any coolant?

 

Even so, there are likely other higher spots in the cooling system (passages in the head/intake, heater core, etc) that air can get trapped in, much like a grease trap in a sink.

Lifting it up is your best bet for air lock.

 

streetrodder13, yes electric fans are not for use at highway speeds. Why would you need an electric fan at highway speed if you had a properly designed and operating system? Ram air should provide adequate cooling. You don't need any fan at highway speed. The electric fans on my 46 Ford convertible only operate when idling. They usually come on when it enters the garage. I used to have a 40 Willys with an electric fan that had a switch to turn the fan off at highway speeds. A car that overheats at highway speed has either an airflow or an inadequate radiator.
A car that overheats at highway speeds needs more then burping.

 

If you have a heater in the vehicle,make sure that the heat valve is fully open when bleeding air from the system.My 55 Safari has an under the driver's seat heater core and it is a PITA to bleed air out of.If I have to bleed the system,I open the heater valve and fill the radiator with straight water and leave the cap off and bring it up to operating temperature as when it does finally burp it blows coolant everywhere. After that happens I gradually drain off the water as I'm adding antifreeze and when the petcock starts to flow green(antifreeze color)I close it and top up the radiator. Another thing I have to do is leave a space in the top of the radiator to allow for expansion or it will just blow coolant out of the overflow until it gets to the right level.
If you're heating up while driving that sounds like a blockage in the radiator.

 

I use to pressurize the system with a radiator pressure tester(Stant makes a good one). Let it sit a few minutes.
Then loosen the highest hose I can find.the air blows right out.
Did this on new cars,only way I was successful.
Check the cap if it holds pressure,the most overlooked part of any cooling system.
Hope this helps,Gary

 

X2. Never fails!

 

We have started using restricter plates instead of thermostats and burping is so much easier. No waiting for the thermostat to open and air doesn't have anyplace to hide. The engines run 10-20 cooler too.

Don

 

Wow, I never had the need or even heard of burping a sbc, although a later reverse flow lt-1 is a different story.

OP is your elec fan a dually? ... if so maybe the second fan's relay is dead

 

If you can get to your lower radiator , remove radiator cap and squeeze the lower hose until it quits bubbling. Worked for me.

 

I'm hearing what your saying GMAN and I'm in no way disagreeing with you, but with an airflow or inadequate radiator it just seems to me that it would constantly run hot, which it isn't. When it gets up to 230ish it only stays there 30 to 40 seconds then returns back down to 180. I would think that the aluminum Afco radiator would handle a stock 350 non A/C car. As far as airflow the only thing I've been told to try is put a couple of 1/2" holes in the shroud to make sure that the shape of the shroud isn't creating a turbulence not allowing sufficient airflow. Have you heard of anyone doing this?

 

Asuming there is no kinks at all,even a small one in any of the hoses.;As odd though here,the lower rad hose,can suck closed at highway speed/rpms if it an't a good spring inside and spaced right with in the hose,at the point temp go up enought to make PSI very high,that will some times let hose open again.
One other little note that may note be of any use,is upper hose can on some cars be put on with a hump in it,that hump is a high spot and get full of air/steam making a far size bubble that can move all at ones and then form again.

 

On my O/T 95 chevy truck, I fill up the radiator with the water temp sender out of the intake until I see antifreeze, seal it up and top off the last couple inches while its running. Not doing this, would always trap air and heat up right away.

 

Went the temp spikes up and then goes down does it go back up again when driving or does it run nornal?

 

Nuther vote for drilling the thermostat. 1/8" is big enough that it will cause the car to warm up slowly in the winter though (or so my customers tell me).