How the coolant bleeder valve works
12-22-2014, 03:14 AM
#1
Nordschleife Master
Thread Starter
How the coolant bleeder valve works
Just thought this is interesting and wanted to share with you some pics. I took an "x-ray" view of the reservoir with the valve removed. What's below the valve is an inner opening and a chamber surrounding it.
The vent lines from the radiators and the oil/coolant heat exchanger are connected to the inner opening only. These are the two highest points in the cooling system where any trapped air will naturally migrate to. The outer chamber is connected to the reservoir via that bright vertical slit. The valve is made up of a spring loaded rubber diaphragm that normally presses down and closes the inner opening, preventing any vent air to flow into the reservoir. When the coolant warms up, the pressure pushes up on the diaphragm so any air from the vent line can escape into the reservoir. Any excessive air in the reservoir can then escape via the CAP, which opens at about 18 PSI. The bleeder valve itself starts to open at ~8PSI.
When the coolant cools down, the valve closes to prevent air being sucked back into the vent lines. The system is designed to do one-way bleeding.
After a coolant drain, air is introduced into the system so we need to manually raise the valve to let air burp out of the system when cold. That's why the manual bleeding method works as well, albeit more hassle.
The vent lines from the radiators and the oil/coolant heat exchanger are connected to the inner opening only. These are the two highest points in the cooling system where any trapped air will naturally migrate to. The outer chamber is connected to the reservoir via that bright vertical slit. The valve is made up of a spring loaded rubber diaphragm that normally presses down and closes the inner opening, preventing any vent air to flow into the reservoir. When the coolant warms up, the pressure pushes up on the diaphragm so any air from the vent line can escape into the reservoir. Any excessive air in the reservoir can then escape via the CAP, which opens at about 18 PSI. The bleeder valve itself starts to open at ~8PSI.
When the coolant cools down, the valve closes to prevent air being sucked back into the vent lines. The system is designed to do one-way bleeding.
After a coolant drain, air is introduced into the system so we need to manually raise the valve to let air burp out of the system when cold. That's why the manual bleeding method works as well, albeit more hassle.
Last edited by Ahsai; 12-28-2014 at 02:39 AM.
Trending Topics
11-26-2015, 06:13 AM
#10
Intermediate
Join Date: Nov 2015
Location: Middle of the Mediterranean Sea
Posts: 47
Likes: 0
Received 0 Likes
on
0 Posts
This is amazing, just what I needed, because I have always had coolant stains around my bleeder cap. So I went and bought both o-rings. Only to discover upon removal that the large one was not there (!) and began to doubt whether it is necessary / where it goes. This clears things up nicely.
Some bozo must have assyd without the large o-ring. Result, my coolant only ever saw (say) 8 psi of pressure, what the bleeder valve builds up, as after it opens there is a direct vent to atmosphere.
Guess that was enough, thankfully.
Some bozo must have assyd without the large o-ring. Result, my coolant only ever saw (say) 8 psi of pressure, what the bleeder valve builds up, as after it opens there is a direct vent to atmosphere.
Guess that was enough, thankfully.
11-26-2015, 10:55 AM
#12
Drifting
Beers on me if you're ever in DFW, TX Ahsai. Seriously.
11-26-2015, 02:55 PM
#13
Nordschleife Master
Thread Starter
11-26-2015, 04:56 PM
#14
how do you bleed the system? when I changed the heater core, I filled up and ran the car with the valve up until I could hear the fans turn on. let it run for 10 minutes revving and holding to 2k rpm every once in a while. seemed to work as I never had over heating issues and that coolant smell finally disappeared
11-26-2015, 05:05 PM
#15
Nordschleife Master
Thread Starter
I used the uview vacuum tool so I didn't need to do any manual bleeding. My understanding of manaul bleeding is, you pop up the bleeder valve (so air could escape to the reservoir even before the coolant gets hot) and do what you described. Then keep the bleeder valve open when driving the car for a few days. Keep in mind the bleeder valve doesn't vent to the atmosphere so you won't loose any coolant via it.
Also, you can jack up the rear of the car to encourage the trapped air to migrate toward the reservoir when you rev the engine.
Also, you can jack up the rear of the car to encourage the trapped air to migrate toward the reservoir when you rev the engine.
how do you bleed the system? when I changed the heater core, I filled up and ran the car with the valve up until I could hear the fans turn on. let it run for 10 minutes revving and holding to 2k rpm every once in a while. seemed to work as I never had over heating issues and that coolant smell finally disappeared