We chewed up several impellers before we learned not to run them until the water stops flowing. Now we check every year and replace every other. But for the past two years we've had sketchy cooling. We've been running hotter than normal and the tailpipe flow just didn't seem to be all there.
Rather than breaking everything apart, I wanted to try the simple approach first... and I think it worked!
1. Disconnect the raw water pump outlet.
2. Disconnect antisiphon inlet. (this means you're back flushing through the oil cooler because the oil cooler inlet hose is about 2 inches and would be tough to remove)
3. Get a bucket and a hose with a jet nozzle
4. Press the jet firmly into the antisiphon hose and watch the chunks flow out.
5. Change directions for a few seconds when you stop getting chunks to shake things loose. And every now and again blow on the hose until the circuit dry so you can guage the resistance.
6. Repeat 4 and 5 until you get three consecutive clean buckets and you can blow freely.
The setup...
The results... 19 in tact impeller vanes and lots of little chunks.
Hopefully we've now payed for the sins of the past and will never need that process again. But if you find your cooling flow stops, this is a good quick first step.