Removing air from cooling system

Snosport

Veteran Member
Joined
Jun 5, 2002
TDI
2004 Passat
I just replaced the radiator on my 2004 Jetta TDI following a deer collision. All of the coolant out of the block may have been lost when the lower hose was removed. When I refilled it I was able to add only about 1/2 gallon of the coolant water mix.

My concern is that there is almost certainly air in the cooling passages in the block. I need to know if there is a good way to bleed off the air so that the coolant fills the passages in the block before I start the engine.

Any help would be appreciated.
 

cyrus #1

Well-known member
Joined
Nov 20, 2010
Location
St. Albert, AB
TDI
2005 Jetta TDI
What I usually do is remove the upper rad hose and fill as much as I possibly can on both the rad and engine side. Then I will fill the coolant overflow tank to max capacity and "burp" all the major coolant lines for a while. After this I fill the overflow again and start the engine. While the engine is slowly warming up I will continue to burp the system as the coolant circulates.

All that is left at this point is to monitor the coolant level for a couple of days. This procedure has served me well on all of my VW's. I never seem to use quite as much coolant as I think I should though. You are making sure to use the G12 coolant, correct?
 

Snosport

Veteran Member
Joined
Jun 5, 2002
TDI
2004 Passat
I started it up and ran it for about 15 minutes and almost none of the coolant from the reservoir worked its way down.

When I started burping the hoses, I noticed that I have a leak where the top fitting that the top radiator hose attaches to goes onto the radiator fitting and is held in place with spring clip. If I squeeze the hose, it leaks around the the plastic fitting between the fitting and the radiator.

I am using the VW G-12 coolant, but I cheaped out and bought an aftermarket radiator. If I don't find any other cause, I will probably take it apart and replace the cheap aftermarket radiator with a genuine VW.
 

Powder Hound

Top Post Dawg
Joined
Oct 25, 1999
Location
Under a Bridge, Crestview, FL, USA
TDI
'00 Golf 4dr White 5sp, '02 Jettachero 5sp, Wife's '03 NB Platinum Gray auto(!)
... I cheaped out and bought an aftermarket radiator. If I don't find any other cause, I will probably take it apart and replace the cheap aftermarket radiator with a genuine VW.
This is probably what you'll have to do, unfortunately. Looks like you may be a C.R.A.P. victim.
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
I just replaced the radiator on my 2004 Jetta TDI following a deer collision. All of the coolant out of the block may have been lost when the lower hose was removed. When I refilled it I was able to add only about 1/2 gallon of the coolant water mix.
My concern is that there is almost certainly air in the cooling passages in the block. I need to know if there is a good way to bleed off the air so that the coolant fills the passages in the block before I start the engine.
Any help would be appreciated.
Recently with great success post cooling system maintenance I have added as much coolant to the coolant reservoir as I possibly could(approx 1/2 gallon), put cap back on, remove small upper hose from reservoir, attach a small hose to reservoir nipple that is now vacant, and gently blow(w/ regulated compressor air or by mouth). This puts air pressure on the coolant that is in the reservoir and forces it into the lowest coolant passages until it is pretty much 90% full. Repeat process as necessary until coolant comes out of small tube disconnected from reservoir. Worked like a champ for me :)
 

josh8loop

Veteran Member
Joined
Sep 15, 2009
Location
Vero Beach, Fl.
TDI
2002 VW Jetta TDI Manual(performed 01M to 5-speed swap) - 183,000 miles and climbing!
I started it up and ran it for about 15 minutes and almost none of the coolant from the reservoir worked its way down.
When I started burping the hoses, I noticed that I have a leak where the top fitting that the top radiator hose attaches to goes onto the radiator fitting and is held in place with spring clip. If I squeeze the hose, it leaks around the the plastic fitting between the fitting and the radiator.
I am using the VW G-12 coolant, but I cheaped out and bought an aftermarket radiator. If I don't find any other cause, I will probably take it apart and replace the cheap aftermarket radiator with a genuine VW.
I hope no damage was done to the engine from running 15 min with hardly any coolant circulating. Also, you may have to replace the internal 32x4 mm O ring in the upper coolant hose that attaches to the radiator. This is the O ring that seals the plastic quick connect to the upper radiator nipple, and often times leaks due to age( flattens out). Order two and do the lower hose while your at it! :)
 
Top