Radiator overflow hose/nipple - what's it for?

Tom Mullane tmullane at snet.net
Wed Jul 24 08:51:10 EDT 2002

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Years ago a bought 1983 VW GTI.  The car would overheat within minutes of s=
tarting.  I changed the t-stat and water pump with no change.  When I remov=
ed the overflow hose to change the radiator, I discovered that the PO had r=
eplaced the nipple on the rad  for the overflow hose (I assume it some brok=
e off) with a bolt.  He/she then cut the head off the bolt and shoved the h=
ose back on to it.  I drilled a hole through the center of the bolt and rei=
nstalled the hose.  Problem solved.

Conclusion:  The overflow hose is an active component in the cooling system=
;  take the cap off the overflow tank while the car is running and watch ho=
w much fluid actually passes through it.

Message: 12
Date: Tue, 23 Jul 2002 22:31:07 -0400
To: "Doyt W. Echelberger" <Doyt at buckeye-express.com>
From: Dave C <conner at cfm.Ohio-State.edu>
Subject: Re: Radiator overflow hose/nipple - what's it for?
Cc: quattro at audifans.com, 200q20v at audifans.com

At 10:00 PM 7/23/2002 -0400, Doyt wrote:
> For one thing, when the coolant in the engine and radiator heat up and
>coolant can flow from the radiator into the translucent overflow tank and
>compress the air in that tank. AND, excess pressure in the radiator beyond
>the 17-22 lb limit can be directly relieved by the valve in the pressure
>cap on the expansion tank.

But ... there is another hose connecting between the bottom of the overflow
tank and the radiator that would continue to serve this purpose.  Wouldn't
it?  This hose and a bleed screw in top of the radiator seems to be
sufficient for the 4kq.  I think the overflow hose really only serves to
let escape from the system, that's why it's at the highest spot on the
radiator.  It's only advantage over the 4kq is that no human needs to
remember to open the vent.

>Next question: Without the tube, how could air escape from the upper
>chamber of the radiator

  If I sealed up the hole with a threaded bolt it would be removeable and I
could let air out whenever the system had been drained, etc, same as the
bleed screw on the 4kq.  Inconvenient because I'd have to remember to do it.

>And your fix sounded like it made sense. ...
>Maybe not in the upper rad hose, but in the offshoot line to the turbo
>coolant pump.
>Doyt Echelberger

I think it needs to be the highest part of the radiator to let air out.
Maybe a tire valve is the solution... popped into a hole drilled into short
length of 1 inch ID copper tubing and spliced into the upper radiator hose.
 OTOH ... if it's only purpose is to let air out, then I might thread a
bolt or screw into the hole left by the broken nipple and unscrew it when
there is a reason to think air might be in the system.  This is how I would
seal it up anyway, even if I do install the copper tupe with nipple into
the upper radiator hose.

Thanks for the reply, Doyt.
Dave C.


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