Tracy - I suppose the new pump could be weak. I just changed the water pump on a 3rd generation Accord and noticed quite a difference in the shape/design of the impellor blades. I've read elsewhere that this can affect coolant flow.
I replaced with a dealer item; the blade design on this item looked as though it could provide better flow.
I wonder if perhaps your new pump doesn't flow as well as it should?
My 2 cents.
1991 300-SEL - Model 126
M103 - SOHC
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