I know there are quite a few threads on this topic already and I still am unable to flush my wife's 2004 4runner(V6). I drained the radiator (couldn't find engine plugs). Only got out 1-2 liters. I removed the upper hose from the radiator and tried to flush water through from the garden hose but it wouldn't go through. I ran the engine with heat on for quite a while (30 min) and never was able to get water into the radiator.

Out of curiosity, I left the cap off but reattached the upper hose with the engine still running. After revving the engine to 2.5-3k RPMS I saw the coolant coming through. So, the thermostat is not stuck but I can't flush.

Any ideas on whats wrong with the truck or with me?

Thanks.

 

If you take the thermostat out, you should be able to flush the engine with no problems (although that's a bit extreme).

1-2 liters by draining the radiator?!? Are you sure it was empty when you were done? If your thermostat has a jiggle valve, you should be able to drain most of the engine coolant from the radiator drain (through the jiggle valve), although it's a very slow process that way (it will just dribble out of the radiator drain hole).