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

Dave C conner at cfm.Ohio-State.edu
Tue Jul 23 23:31:07 EDT 2002

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.

>Good question, Dave.
>>   I think the
>>overflow setup is similar on the 4kq as far as the tank and pressure cap.
>>But instead of the overflow hose the 4kq has only a vent with a screw in it
>>... used to vent air from the system.  I think my radiator is solid aside
>>from this broken nippleotherwise... I just wiggled a bit too much on this
>>little plastic thingy while flushing the coolant and messing with the hose,
>>If this overflow hose is actually important/useful could someone suggest a
>>way to repair it?  I've not heard of a kit.  I'm thinking it might work to
>>splice a short piece of 1 1/4 inch OD pipe into the radiator hose with a
>>nipple attached to it somehow, and run the hose to it, then screw a plug
>>into the hole where the nipple used to be.  I haven't figured out which
>>types of pipe are available in the right dimensions or how to attach the
>>nipple.  If it turns out the overflow hose is unnecessary I'll be happy to
>>save myself the trouble.
>>Dave C.

More information about the 200q20v mailing list