Bleeding all the air out of a Subaru cooling system is undoubtedly an endurance event, it should be an Olympic Sport.
It would appear that a vacuum fill of the cooling system, would be the most ideal method. Which theoretically could mean no burping required. There seems to be a few workshop tools out there, however probably costly for DIY.
* for the models that have them, don’t forget the bleed port on the Heater hose line*
I think a similar setup could be achieved using a mityvac hand pump, which is more affordable, and more likely to come in handy for many other tasks on and off the car. All that would be needed is the mityvac (pressure/vacuum model), radiator cap adapter (which mityvac also make), some hose and a ‘T piece’ adapter (between mityvac and radiator cap, with another hose going into the new coolant bottle). Pinch off hose to coolant bottle, then pull a vacuum on the cooling system. When sufficient vacuum is reached, un-pinch the coolant bottle hose, and there you go.... coolant in, no air. If you run out of vacuum, pinch off hose again, and pull more vacuum.
Alternatively...
Fill cooling system, leaving a little space in the header tank. Using mityvac, pressurise system (don’t exceed normal working pressure), then pull a vacuum (careful not to suck up any coolant). A series of these seems to pull the trapped air out, and may work even better with squishing the radiator hoses to give the air bubbles a nudge.
If you don’t have a mityvac, I found you can get a similar result, by placing your hand over the radiator filler. To slightly pressurise, simply put your hand over the opening (to create a seal), and squeeze the hose. To pull a slight vacuum, squeeze hose so that coolant is just at the top of the filler, place hand over the opening, and let the hose go quickly (the faster the hose expands back, and the greater the displacement, the better). Alternate to other hose(s), when the coolant level stops dropping. Would probably work better if overflow line was blocked off, or pinched (but I didn’t).
If radiator hoses are old, cracked, stiff... etc. excessive squeezing may cause further deterioration. So caution should be exercised, as it could weaken the hose, and lead to a blown hose.
It would appear that a vacuum fill of the cooling system, would be the most ideal method. Which theoretically could mean no burping required. There seems to be a few workshop tools out there, however probably costly for DIY.
* for the models that have them, don’t forget the bleed port on the Heater hose line*
I think a similar setup could be achieved using a mityvac hand pump, which is more affordable, and more likely to come in handy for many other tasks on and off the car. All that would be needed is the mityvac (pressure/vacuum model), radiator cap adapter (which mityvac also make), some hose and a ‘T piece’ adapter (between mityvac and radiator cap, with another hose going into the new coolant bottle). Pinch off hose to coolant bottle, then pull a vacuum on the cooling system. When sufficient vacuum is reached, un-pinch the coolant bottle hose, and there you go.... coolant in, no air. If you run out of vacuum, pinch off hose again, and pull more vacuum.
Alternatively...
Fill cooling system, leaving a little space in the header tank. Using mityvac, pressurise system (don’t exceed normal working pressure), then pull a vacuum (careful not to suck up any coolant). A series of these seems to pull the trapped air out, and may work even better with squishing the radiator hoses to give the air bubbles a nudge.
If you don’t have a mityvac, I found you can get a similar result, by placing your hand over the radiator filler. To slightly pressurise, simply put your hand over the opening (to create a seal), and squeeze the hose. To pull a slight vacuum, squeeze hose so that coolant is just at the top of the filler, place hand over the opening, and let the hose go quickly (the faster the hose expands back, and the greater the displacement, the better). Alternate to other hose(s), when the coolant level stops dropping. Would probably work better if overflow line was blocked off, or pinched (but I didn’t).
If radiator hoses are old, cracked, stiff... etc. excessive squeezing may cause further deterioration. So caution should be exercised, as it could weaken the hose, and lead to a blown hose.
