The pumps definitely changed in 1987. From the parts manual: 1981-1986 w. 2.5, J8134321, Export 1987-1990 w. 2.5, 83502957, Export (w/o Serpentine Belt Drive) 1987-1990 w. 2.5, 83502938, Export (with Serpentine Belt Drive) I suspect the impeller vanes are different, the pump is pushing rather than pulling. Or it's rotational. I don't remember when these engines switched the pump rotation.
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