How can you tell what size impeller the water pump uses without removing it? I have an 84 5.0 CFI if that helps.

 

Just curious, why would you want to know that? Or are you looking for a flow rate for comparison?

 

Take the backing plate off and measure the O.D. is the best way. Or you might find your part number and have someone w/the exact same pump measure thiers. And if its OE.. don't assume an aftermarket impeller will be the same. Sometimes they will increase the diameter or use a vane that is more perpendicular to the flow to increase overall flow rates.

If you have specific Qs.. just ask. I'm sorta an expert on Ford WPs. ;-)

 

I need a new one but there are 2 different ones that come up. I just want the correct one. Unless the larger impeller works the same and is better.