Draining the old coolant and flushing with fresh water went pretty well.  The problem is air trapped in the system.  I thought I = followed proper procedures.  I filled the expansion tank with fresh = phosphate-free coolant while running the engine at 3000 rpms, with the radiator bleeder = screw open three turns, the engine bleeder valve opened and the front end = raised about 16 inches on ramps and a sloped driveway.  Front and rear heate = valves were fully open.

 

The engine was run long enough for the thermostadt to open, with = the temp guage showing in the middle range.  The expansion tank was full, = with air coming out of the radiator bleeder screw, but no coolant was even = sputtering out.  The fill tank was also filled to the correct level.

 

I then replaced the expansion tank cap and shut off the engine in = order to try Darrell Boehler's bike pump technique.  I took off the small = connecting hose from the expansion tank cap and hooked up a proper sized plastic = hose fitted to a bike pump.  When I pressurized the system with a few = strokes on the pump, the radiator gurgled with the sound of escaping air through = the bleeder screw.  The coolant level in the expansion tank dropped to = just below the level of the top large coolant hose, but would not drop any = further even though I tried repeated cycles of pressurizing and allowing air to = escape out of the radiator bleeder valve.  I also had my assistant = continue pumping while I observed air escaping from the bleeder valve (gurgling = sounds, but no coolant drips) although the coolant  in the expansion tank = stayed pretty constant at just below the level of the top large coolant = hose.  I tried the bike pump technique several times, first with the engine = bleeder valve open, and then with it closed.  Continued pumping of the bike pump = did not cause the expansion tank coolant level to drop any further, even though = air continued to escape from the radiator bleeder screw.

 

My suspicion is that there is a crack near the top of the plastic = expansion tank.  When the radiator bleeder screw was closed, the bike pump disconnected, and the small connecting hose re-attached, the expansion = tank coolant level stabilized about 1" below the top of the tank (which = is above the top of the large coolant hose), which is exactly where it had been = for months with the old coolant.

 

My major concern is burping enough air out of the system so that = the engine does not overheat due to air pockets in the coolant.  This already = started to happen once during a test run, but this was at least partially solved = by adding more coolant, as the level in the expansion tank had dropped a = few more inches then.  Now the temp guage is still running too warm, about = 1/2 way between its normal position of dead center and the high temp warning = area on the right side.

 

Is my problem that I didn't give either the 3000 rpm or the bike = pump techniques enough time for the air to bleed out?  Should I have = removed the radiator bleed screw instead of just loosened it?  Is the engine = bleeder valve suposed to be open or shut during the bleeding process?  = Could a crack in the expansion tank be a partial or complete cause for all of this?

 

For now, (overnight) the van is back up on the front ramps, with = the radiator bleeder screw and  the engine bleeder valve both = closed.  My hope is that the air will naturally congregate at the top of the = radiator where it can easily be released through the bleeder screw, using the bike pump = technique with a cold engine.  Also, perhaps the overnight cooling = and de-pressurization of the engine will contract the coolant enough so that = I can add more coolant to the expansion tank.

 

All help will be greatly appreciated, especially fast responses, as = my buyer is most anxious to get his van for this weekend, and I am most = anxious to get paid for it.