Purge Air from Radiator

[YFC]

How do I Purge the Air from Radiator on my 1998 2.5 liter Outback engine after flushing and refilling? Are there special tricks?

[NOMAD327]

It normally drains a bit better going slightly downhill, and fills a bit better going slightly uphill. I would replace the thermostat if it's been a couple years. Use only a genuine Subaru thermostat. The best engine drain is accomplished by removing the thermostat which is at the bottom below the water pump. All that said, I get pretty good results on level ground. The refill trick is to put a few quarts in the radiator and then remove the top radiator hose. pour coolant down the hose into the engine until the hose is full. then hook the hose up and fill the radiator. You will get at least 90 percent full this way, enough to eliminate any danger of overheating the engine while the motor is warming up the first time. There is a small air bleeder on the top of the radiator passenger side, but I have never needed to do more than these steps. Run the motor till it warms up and the thermostat opens, and you will then need to add just a bit more water to top it off. A good flush will include draining the overflow tank and putting some new mix into it along the way, and I always make sure the heater is giving off heat while I am waiting for the thermostat to open the first time.

[Dr. RX]

I use an old drag racing trick, air usually gets trapped at the thermostat, on most of the thermostats I have installed in EJ series engines, there is a check flow valve (a wierd looking thing at the top of the thermostat throught a hole). The old drag racing trick is to drill small holes at the top of the thermostat, this allows the air to pass through, what I do is just cut the flow valve off, leaving the hole it goes through. This allows the trapped air to pass through even if the thermostat is closed. Make sure that you install the thermostat with the hole pointing up.

[YFC]

Thanks to both. I will try. Initially I did the "fill the top radiator hose" trick, but still seems to be trapped air. Hope!!!! I haven't damaged the Head Gaskets. YFC

[99obw]

I just flushed the outback last weekend. I put the car up on ramps, drained as much as I could get out, then flushed the system with distilled water with the engine running until the water coming out runs clear (6-8 gallons). Then I drained all of the water I could get out of the system, then added half of the system capacity of full-strength coolant and topped off with distilled water. I used a cooling system funnel and opened the radiator bleeder periodically to let air out. Works great every time. No need to fiddle with the upper radiator hose. Also, clean out the overflow and fill 2/3 full with 50/50 mix, a little air will be worked out of the system over the first few thermal cycles, so the level in the overflow will come down a bit.

[blitz]

Do Impreza's not have the air bleed screw on the radiator?

 

I don't see them on either of mine.

[Setright]

My Imp doesn't.

 

However, it does have that bulge around where the rad cap and top hose mount on the radiator. Reckon Subaru has put that bulge there to collect the air. Highest point in the system..

[Dr. RX]

My pre-2001 WRX doesn't.