In spect the impellor closely, they are known to deteriorate over time. Check that it rotates when engine cranks, even grab impellor and try twisting it to be sure the gear isn't stripped, it's plasdick too. X-2 on pro cleaning of rad. If it still gives problems after this you may have to tear motor apart to clean dirt that has settled at bottom of water jackets on cylinders, I don't think any amount of backflushing/cleaners will remove sediment and dirt there. If you pull clutch cover be sure to use a new O-ring on the water tube that comes out the back of the pump. I:I