Bleeding cooling system air

Hi,

I think we all know how Subies are about trapped air pockets when
refilling coolant...

I also have an old Toyota truck w/ the 22-R engine, which some of you
know is also a problem child WRT trapped air. I've had a couple of 'em,
and they've given me fits at every coolant change. I've gone thru all
kinds of gyrations, and stumbled on this idea totally by accident, but
it's worked quite well at the last coolant change and again the other
day when a new water pump went in. My Subie's dead right now, but I'll
try this trick on it when I put it back in service.

I took an old radiator cap, and drilled a tiny hole (maybe a half
millimeter?) in the little metal piece in the inner center of the cap.
This is the piece that stays closed under pressure (engine hot), then
opens under vacuum (engine cool) to allow coolant to flow back from the
overflow tank. You can identify it by pulling--it will open under spring
pressure. Drill the hole toward the center (inside the sealing ridge at
the outer edge.)

Once the system's been refilled, install this cap instead of the normal
cap. Run the engine to normal temps w/ the heater on full and all the
usual precautions (front of car higher than rear, watch the temp gauge
carefully and all that.)

What's happening is the system is essentially "open"--it holds no
pressure--BUT w/ a cap installed you don't have the violent bubbling and
eruption of coolant all over the place you often get if you run w/ no
cap. This seems to help the coolant flow thru the system more easily
than if it were under pressure, allowing air to move out of the nooks
and crannies where it often gets trapped.

Shut the engine off, let it cool, refill as required. Repeat the cycle
once and cool again. Check again, refill again as required, install the
proper cap, and test drive. Watch coolant level for a couple of days and
top off as required.

Hope this helps some of you who've been scratching your heads over
trapped air...

Rick

 

Can you post a link to a photo of the drilled cap? Your idea sounds very
interesting.