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Cooling System Bleeding Procedure

Posted by exgm (My Page) on
Fri, Apr 3, 09 at 17:54

I'd like to know whether todays 'vacuum' cooling system flushing equipment can fully evacuate all the air from a system once it's been drained down. Specifically, relating to the GM 3.1/3.4 series fwd engines. On this engine there are coolant bleed screws on the themostat housing and one at the top of the riser on the LHS of the engine. I have been assured that the LHS screw need not be opened during the process, but then, precisely how does air trapped in there get removed by today's equipment?


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RE: Cooling System Bleeding Procedure

The 'Air Lift" tool has been an absolute blessing when it comes to working on the coolant systems of today's cars. With all of the spots where air can be trapped and be very difficult to bleed out, the air lift solves this problem by creating a vacuum in the coolant system that is comparable almost to what we used to get when we would evacuate an AC system years ago. (We evacuate AC systems much deeper today) The air lift tool can easily achieve 25" hg vacuum in about a minute on most automobile systems, and vehicles with dual heater systems in as little as two minutes. The tech can leak check the coolant system by watching to see if the vacuum bleeds off in as little as five minutes.

From there to fill the system have the engine coolant ready to add to the engine. Attach the fill hose and let the vacuum built into the cooling system pull and completely fill the feed hose. This bleeds air from that hose and the tech then can lock it full of coolant. Now change hoses back to the evacuate hose and pull a second vacuum on the cooling system. This removes the air allowed in during the purge phase of the fill hose. Now the tech reconnects the fill hose and then allows the coolant to be sucked into the engine cooling system. Of course in reality, the air pressure in the atmosphere pushes the coolant into the engines cooling system. Because the entire system is pulled into a vacuum, every bit of the system accepts coolant. One trick is to get the last bit of coolant required to fill the system completely to go in faster is to lift the coolant bottle and let some siphoning action help. With the air lift we no longer have to open heater core hoses to bleed heater cores, (neither front nor rear cores). We don't have to be concerned about air pockets near thermostats or anywhere else.

The tool literally saves a half an hour per car in monitoring and/or bleeding time from any service that required the cooling system to be opened.


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RE: Cooling System Bleeding Procedure

Thanks john_g , much appreciated.


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