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#1 Old 01-07-2011, 03:49 PM
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Bleed coolant system

I did a radiator flush today but still think I have air pockets in the lines, at first I had no heat so I went back and disconnected a few of the lines and got some air out. After that I had heat but still seams like I got a lot more coolant out than what went back in. Anything I should check to be sure. Thanks
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#2 Old 01-07-2011, 08:20 PM
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did you drain from the bottom of the block too?
As far as I am aware, there is no "air bled valve" I have always just filled and run and topped off as needed.
after the initail fill, and there is a decent safe level, i will run the van as I fill while squeezing the top hose to help things along, and then watch it for a couple days...

1991 Previa (lexus EGG 240) 5 speed manual trans, spoiler, 18"wheels,tint,
1995 "FrankenYota".S/C, dual roof, 5 speed, 4x4 (2wd,4h,4low) lifted
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#3 Old 01-07-2011, 09:33 PM
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Dano, two things...the Previa has a shut off valve...a ball valve of sorts if you will. It is on the intake port of the heater core under the hood. It has a cable that is attached to the temperature slider on the control panel inside the vehicle. When you choose cold air (as in summer) it shuts off the flow of heated engine water to the heater core. When you choose hot air (as in winter) it fully opens the valve allowing the heated water to flow through to the heater core. If, in your flush process you did not push the slider to the hot side then you most likely left the liquid present in the heater core there. If this is what you did and you flushed the engine with the slider in the cool position and then refilled the system with coolant then there would have been an air pocket created at the inlet valve. If after you refilled the cooling system you then positioned the slider to the hot position this would have allowed coolant to flow through the heater core along with the air. Because the plumbing on the Previa is elaborate the self bleeding process will take a while.

This is irrelevant and here is why. The engine is below the radiator cap. This in and of itself allows the system to be self purging. If in fact the engine is higher than the radiator cap then there will be a bleed screw in the system at the highest point in the piping from the engine to the radiator. This is where the air will collect. The mid engined Pontiac Fiero is one example. The Alfa Romeo Spyder is another. These cars cooling systems must be air bled in order to achieve the correct cooling pressure because they cannot self bleed due to the relationship of the radiator to the engine.

When you finally get the air out of the system and it is completely filled with coolant then and only then will it pressurize. If not pressurized it will not funtion properly. Therefore, if there is a blown head gasket or a cracked head or any other internal compromise then the cooling system pressure will leak into the part of the engine that is compromised. If the cooling system is compromised in a fashion that allows coolant to leak to the outside then the same consequense is present. An unpressurized cooling system. This will inhibit proper flow. Especially to the parts of the system which require the most on the pressure to push it through...such as the heater core. Resulting in incomplete heating due to a lack of flow. In addition, the heater core's structure is much smaller than the radiator allowing mineral deposits to come to rest there much easier than in the radiator...exaserbated by the fact that when the slider is in the cold position there is no coolant flowing through the heater core. And yes, this allows stagnant coolant to sit and settle and do it's damage.

Did you do a pressure test on the cooling system yet?

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#4 Old 01-08-2011, 07:21 PM
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I had the slider on the heat position when I did the flush, so that shouldn't be an issue. How do you do a pressure test on the cooling system? Would the leaking heater core cause improper cooling you describe? The heat is working fine other than the slight smell of coolant from the leak but I have a heater core on it's way. Since the flush the strange water gurgling sound that was coming from the dash has gone away which makes me think it might have been caused by air in the system from the leak.
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#5 Old 01-08-2011, 08:07 PM
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The rushing sound is in fact air and water traveling through the system alternatively. This sound won't be heard when there is no air in the system. Any leak in the cooling system regardless of where it is will depressureize the system causing reduced cooling effect simply because of air being introduced into the system. The pressure tester is mounted in place of the radiator cap. The first test will be with the engine cold. Pump up the pressure to 7-10lbs. and observe the gauge and if there is leakdown indicating an obvious leak somewhere. Then release the pressure but with the tool installed start the engine and bring it up to temp. Observe the pressure of the gauge. If it climbs to 15 or more lbs. then you will have an indication of either a blown head gasket or a cracked head exists. This will mean the combustion pressure of the cylinder is being pushed into the cooling jacket either through a crack or the compromised gasket and is increasing the pressure in the cooling system. This problem increases by multiples at highway speed.

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