Date: Mon, 13 Oct 2008 08:12:40 -0700
Reply-To: mdrillock <mdrillock@COX.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: mdrillock <mdrillock@COX.NET>
Subject: Re: Removing radiator bleeder screw
In-Reply-To: <1223903435.30931.1278989849@webmail.messagingengine.com>
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No it doesn't because if you open the reservoir the thermal expansion
pressure will be lost. You need to first let the contained pressure blow
any air out of the the radiator. After you see just coolant coming out
of the rad bleeder, close it. If all the pressure comes out and air was
still coming out you need to do the process again until just coolant
comes out. This method is easily done with the engine off as long as it
was warmed up first. You need to let it cool between attempts and top
off the tank when it is cool. This is only for getting the last air out,
not as a primary bleeding process!!
One person can also do a complete refill and bleeding without any help.
Understanding the principles of the process is key to doing this. That
seems to be lacking here of late.
Filling the whole system is another matter. The waterpump will try to
push coolant to the radiator but the closed thermostat blocks the
radiator return hose so it can't fully do it. The waterpump is fighting
this back pressure while the cold thermostat is closed. That is why the
bleed screw on the radiator is SO important. Opening the screw lets the
waterpump push coolant into the radiator even with the thermostat closed
since the trapped air now has somewhere to go. Once the radiator is
filled to near the top the coolant spills over inside it into the return
pipe, filling the return line and much air from it flows the other way
up to the bleed hole. Once no more air is in there getting displaced
with coolant the coolant starts to spill from the bleed hole and the
bleed should be closed. I prefer to remove the bleed screw for this
initial filling since this speeds up the process. Once coolant comes out
I put it back and just loosen as needed during the rest of the bleeding.
Raising the front of the van adds more gravity effects to the forces
that the waterpump must overcome to fill the radiator. That is why the
'official method' requires reving the engine more than my approach. As
anyone who has done it that way knows, the level in the tank drops
quickly when you rev the engine but coolant spills right back out of the
tank if you back off the rpms. It can be done this way but you end up
with more of a mess until you master the trick of holding the throttle
open slightly while adding coolant and putting the cap back on the tank.
Letting the rpms drop before you get the cap on just lets coolant drain
back out of the radiator and spill on the ground so bleeding must be
done again. The raised front method is best done by 2 people but one can
learn to manage it. The bleeder on the radiator must be open to let the
coolant fill everything with the thermostat closed, whichever method you
use.
Sorry, this is not as clearly written as I would like but I am out of time.
Mark
Allan Streib wrote:
> "mdrillock" <mdrillock@cox.net> said:
>
>
>> You don't need to remove the bolt to get the air out. Once the engine is
>> running and warmed up the coolant expands and pressure builds in the
>> system with the cap relief valve set at about 15 psi. If you then
>> loosen the radiator bleed bolt a turn the pressure in the system will
>> release out of the radiator bleed hole, pushing out air if any is there
>> or coolant if not.
>>
>
> That makes sense; I'll give it a try. The problem is doesn't that
> require a person at each end of the van, one to operate the bleed screw
> and one to keep the reservoir from getting empty?
>
> Allan
> --
> 1991 Vanagon GL
>
>
>
