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

Doyt W. Echelberger Doyt at buckeye-express.com
Tue Jul 23 23:57:24 EDT 2002

At 08:34 PM 7/23/2002 -0400, you wrote:
>On the type 44 radiator ... what is the purpose of the overflow hose
>connected from the top of the radiator to the overflow tank?
>My little plastic nipple broke off.  While I'm trying to think of a way to
>repair it I have to wonder why can't I just plug it up?

......let's try to imagine why the engineers put it there. It is a pathway
for liquids, gases & vapors to move between the radiator upper chamber and
the air space in the translucent overflow tank. What does such flow do? For
one thing, when the coolant in the engine and radiator heat up and expand,
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.

Next question: Without the tube, how could air escape from the upper
chamber of the radiator as you fill the overflow tank to bring the coolant
level up to the line, perhaps after draining the system, or even just
topping off the system? You would have to have a bleed screw in the top of
the rad, like in your 4kq. Inconvenient.

Without the tube,  it would be difficult to do gross things like draining
and refilling the system. And it would be equally difficult to do fine
tuning of the coolant level, which needs to be done now and then. (I never
have figured out where that cup or two of coolant goes every few months.) I
must have a crack in the tank, or a seeping seam.....or a tiny opening in a
head gasket.....AAAAArrrrrggghhhh!

And your fix sounded like it made sense. When I buy new tires, they put in
new metal filler valves that fit up through a hole in the rim and are held
in place by a nut. Maybe such a valve without the inner valve thing would
work. Drill a hole in the rad tank and feed the tire valve in through the
opening for the upper hose. Sounds risky....drill may crack the tank..No, I
don't like that idea....new idea........Could you put such a valve in the
side of a copper tube, and cut the upper rad hose and put the new section
in place of part of the upper hose? Maybe a lip on each end of the copper
tube, to let the hose clamps get a purchase.

Maybe not in the upper rad hose, but in the offshoot line to the turbo
coolant pump. There ya go!

Good question, Dave.

Doyt Echelberger

>   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.

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