Gates makes hose I.D. reducers, they slip inside a hose to reduce the I.D. by 1/4". Gates 26390 goes from 1.5 to 1.25, 26391 goes from 1.75 to .15, 26392 goes from 2 to 1.75, 26393 goes from 2.25 to 2. I used one in another application where the water pump was smaller than the radiator outlet, they work well.
