air in the rad

[neurottica]

G'day all. I had the intake gasket done recently to my 99 venture and shortly after started having the "tach like" temp gauge trouble. van runs hot and cold yet there is no coolant loss. after reading some threads, i see it could be the head(ack) but id like to try bleeding the air out before committing to huge bucks. could someone tell me the best way to do this?
thanks

[cdru]

The best way would be how shops to it. You hook up a vacuum pump and suck out all the air, then open a valve and let the vacuum draw coolant into the system. Mityvac makes one but it costs around $80 I beleive.

To do it by hand, it take a while. Open up both bleeder screws. Fill up the radiator as full as you can then close both screws. Turn on the vehicle and let it run to normal operating temperature. Open the screw just after the thermostat housing ever so slightly to bleed off any air that may get trapped over on that side. Turn off the engine and let the van cool. Repete several times and the air should be forced out.

As the system heats up, the air becomes pressurized. The radiator cap will hold 15 psi. After that, it will start to vent to the overflow tank. This is normal and you want this to happen. When the system then cools, a vacuum is formed and the radiator cap then opens, drawing coolant from the overflow tank. By doing this several times, you "pump" out the air and then suck back in coolant. If your radiator cap isn't working correctly though, it may never allow your coolant to become pressurized or to allow coolant to be drawn back in.

[neurottica]

Originally Posted by cdru

The best way would be how shops to it. You hook up a vacuum pump and suck out all the air, then open a valve and let the vacuum draw coolant into the system. Mityvac makes one but it costs around $80 I beleive.

To do it by hand, it take a while. Open up both bleeder screws. Fill up the radiator as full as you can then close both screws. Turn on the vehicle and let it run to normal operating temperature. Open the screw just after the thermostat housing ever so slightly to bleed off any air that may get trapped over on that side. Turn off the engine and let the van cool. Repete several times and the air should be forced out.

As the system heats up, the air becomes pressurized. The radiator cap will hold 15 psi. After that, it will start to vent to the overflow tank. This is normal and you want this to happen. When the system then cools, a vacuum is formed and the radiator cap then opens, drawing coolant from the overflow tank. By doing this several times, you "pump" out the air and then suck back in coolant. If your radiator cap isn't working correctly though, it may never allow your coolant to become pressurized or to allow coolant to be drawn back in.

Thanks for reply. so is there a way of knowing if cap is working or just get new one and go from there?

[cdru]

Originally Posted by neurottica

Thanks for reply. so is there a way of knowing if cap is working or just get new one and go from there?

You can pressure test it. Here in the states, AutoZone's carry the pump/adapter to test it. Repair shops or radiator shops may also have one that you could use to test.

Or you could just replace it. It's not an expensive item.