Following the advice of a mate who is an old school mechanic, I removed the water pump belt to stop the water being agitated and creating bubbles. I fitted a half bottle ( I used a threaded male to male joiner siliconned in the neck of an old coolant bottle) to the bleed point near the front top of the block. With the radiator cap on I then Idled the engine for a couple of minutes. When I revved it up (momentarily), the coolant was forced out of the bottle. But mine is an RB30, so a 4.5 is different. Also get the test done in as short a time as possible. I didn't let the engine run for more than 7 minutes, to avoid damage to the block. And the engine was cold before the test. And don't forget to refit the belt! The water pump seal manifested itself as a white salty stain at the bottom front of the engine, and also the smell of coolant when the engine was hot. Hopefully someone who has a 4.5 can tell you how to test it without causing damage.
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