Burping" the engine cooling system

S

scott nutter1

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Jan 5, 2015
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Has anyone found it necessary to"burp" the engine cooling system to bleed out all the air after a coolant flush? Or is it unnecessary on our GMC's?
If it is needed, what would be the best technique?
Thanks, Scott.
--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
Scott, if your pressure cap is the correct one for the GMC, it should be a
9 psi cap. If your expansion tank is intact and working correctly, the
system, if filled to the top of the radiator neck, and the expansion tank
is up to the "cold" level, it should burp itself after 2 or 3 heat/cool
cycles. The coolant will expand and fill the expansion tank to the "hot"
level when the engine is at operating temperature. When the engine cools,
the cap will release and the coolant should fill the radiator to the top of
the neck. If your cap is shot, all of what I said is moot. These caps we
buy today are very short lived. It pays to check them with a tester and
inspect the rubber gaskets frequently. Test the new ones you buy, too.
Jim Hupy
Salem, Oregon

On Wed, Apr 15, 2020, 3:04 PM Scott Nutter via Gmclist <

> Has anyone found it necessary to"burp" the engine cooling system to bleed
> out all the air after a coolant flush? Or is it unnecessary on our GMC's?
> If it is needed, what would be the best technique?
> Thanks, Scott.
> --
> Scott Nutter
> 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final
> drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
> installed MSD Atomic EFI
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Yes. It is necessary. It should do itself after a few heating/cooling cycles through the overflow tank but you’ll have to add fluid.
You should also turn the heater lever on (open the valve if you put one in your heater hose).

Another good way to get rid of the air is to fill using the Preston Flush and Fill Kit. I have been using it in all my vehicles for over 20 years.
You install this in a heater line. It is also a good way to flush your engine rather that just draining it through the bottom valve of the radiator and the side plugs on the engine.

After you have flushed out the block you then pour the antifreeze into your radiator. It will displace water through the T you install in the heater hose. Instructions can be found on the internet or with the kit you buy.

If you want to use distilled water that you pour the proper amount of distilled water in. It will push the tap water out of the T and when you pour in your antifreeze it will force out the rest of the tap water.

You will find that all of the air is out of the system.

Emery Stora

>
> Has anyone found it necessary to"burp" the engine cooling system to bleed out all the air after a coolant flush? Or is it unnecessary on our GMC's?
> If it is needed, what would be the best technique?
> Thanks, Scott.
> --
> Scott Nutter
> 1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
> installed MSD Atomic EFI
> Houston, Texas
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
I fill with half and half antifreeze (be sure you get concentrated, or use the premixed full strength)and distilled water. Run the engine through
three or four cycles and the air is gone. Fail to do this and it will remind you about halfway up the next steep grade you see. It looks like
there's a lot of reserve capacity in our cooling systems, but five tone and change of coach with a toad behind uses it all up on a grade. My coach
will pull Cullowee or MontEagle without histrionics, shows about 200 (180 stat) and holds there on each. Bobtail it will show 185 - 190 on MontEagle.
They're the two grades I regularly run. Coming home from LA when I bought it, the old engine ran about 210 in the Rockies but no more. That was
running bobtail. I flush and refill every three years or so, and usually just buy a new 9 pound cap and toss the old one at that point.

--johnny
--
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
 
Since the heater core is higher than the radiator cap it's harder than some vehicles to get air free. James and Emery summed it up well. Also If the
hose to the reservoir is old (microcracks) it can vent liquid properly but vent air in due to porosity. Then you are always under filled. I went
through 3 new caps on my Jeep before I got a good one in all criteria . The center mini spring on the poppet valve (hidden) will often fail first.
Then the valve hangs open and coolant comes and goes with no pressure. I ran into a new batch of 3 Gates caps missing the springs entirely! Purchased
same cap as a Carquest rebox and they were fine! Check the poppet by shaking (rattles) and you can see if there is tension with a fingernail. Usually
an off car pressure cap tester puts the cap upside down and gravity will close a defective poppet giving a false "good".
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Great info.. thanks again, Scott.
--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
Or the thermostat is opening and causing a real 10 degree swing which is probably normal. Many gauges also have some delay built into them so if one
is bouncing and one is not then it might be a delay in the slower gauge. If it is truly electrical I would be looking at the cleanliness and tension
issue between the wire contact and the sensor.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
> Great info.. thanks again.
>
> One last question. I have 2 water temperature sensors. One to a gauge, and the other to my EFI computer. Both are Plumbed into the intake at
> different ports. The EFI readout is steady from 175* to 185*. But the other round dial gauge reads pretty steady, but will jump 10* then return to
> steady within 10 seconds. I was thinking it is trapped air... but if all the air is out of the system, maybe the sensor is bad? Or possibly the
> wiring is grounding out?
> Thoughts??
> Scott.

Scott,

Assuming it is not an electric problem (which it easily could be), don't worry about it.

Without heroics, there is never a cooling system that has no air in it. There are other things that can cause this too.
What is happening is very symptomatic of a sensor in a sequestered section. The flow is isolated and then something (anything) changes and it is no
longer isolated. It happens all the time, but in a lab setup, we can see it better. The sensors are low mass thermocouples that respond very fast.
Even if it sets off an alarm, there is always a cover system so it is reported but not acted on immediately like a loss of lube oil pressure would be.


Sorry, this is an hour later than I started because I was interrupted by a phone call.

Matt

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Immersed coolant sensors when in air pockets USUALLY read lower than actual. If you've every done a severe overheat situation after it pegs, and you
keep driving and have lost coolant the gauge drops to cold even though engine is severely overheated. Example was a 74 350 Corvette I limped home like
1/4 mile at a time w no coolant. Once leak fixed and fresh coolant and oil, no noticeable damage sustained.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Yes,
I'm suspecting it's the jumpy temp gauge's sending unit, or the wiring out of it. I replaced the engine water pump over the weekend, and there is a
big chance I damaged the sensor while replacing the pump. I didn't have the issue before the pump exchange.
Scott
--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
Since you just replaced the pump I would guess that it has something to do with that replacement. I assume your temp gauge sender is mounted on top
of the intake manifold and was not disconnected and removed.

So the problem is probably air still in the system. If this is true, a few drive cycles to a complete warmup and cool down again should do it. I
would drive it the way it is and see what happens over a few long drive cycles.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
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