on the driver side ...reach ya hand up under and you should feel a butterfly type bolt.
If it does not have a drain plug, just simply remove the lower radiator hose.
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Drain radiator at bottom or rear of radiator
the 2002 Pontiac Montana came with a 3.4L engine.
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2002 Montana Seat Repair
Where
Drain plug either at the bottom or rear of the radiator or remove the lower radiator hose
under the radiator.
On the radiator...
How much does it cost to replace a radiator in a 2002 Pontiac Grand Am