while I won't recommend it, I flushed mine out once.
I laid the radiator down and filled up the oil cooler with engine degreaser I think. Let that soak for a while, then lifted it back up vertical, drained the gunk out, then got the garden hose after it. Sprayed the hose into the upper port full blast, as hard as I could. Let it run for a few minutes, then started catching samples of the water coming out in a glass jar. It took quite a while, but once I caught several samples in a row that had no metal in it (that I could see anyway), I decided it was clean. Ran the water through it both ways to make sure.
In theory, this should do the trick. Oil going through the cooler HAS to go through the filter, so if you leave some metal, it *should* get caught. But if the oil filter has an internal bypass (and apparently most do), then if that bypass ever opens up you could send metal shavings through your engine. Due to that potential, replacing the cooler or running an external cooler is the best way to go.
As for that engine, it ran great for a while, but after 10k miles or so I started losing oil pressure and pulled it. Lots of wear on the #1 cam bearing was the culprit. I don't think it had anything to do with flushing the cooler though, I think I had other issues that was causing the wear. None of the other bearings showed any signs of foreign material getting circulated, they all looked great.
John
