what would be the cause of a radiator cooling fan not coming on?

Sometimes it may take SEVERAL MINUTES for the fan to turn on.. *SEVERAL MINUTES* ! ‘IF’ the air conditioner is operational - when it is engaged the fan should turn on more quickly.

yes. It will get so hot that it starts spewing antifreeze and the fan will still not engage.

“IF the air conditioner is operational” - turn it on to see if the fan will turn on - that uses a different circuit for cooling fan ‘activation’ as opposed to engine temperature.. Now IF the a/c is inoperative as well - this test will be invalid as it requires inputs from the a/c compressor high pressure switch.

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