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Testing a Radiator for Leaks

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By Tony Cimorelli - November 16, 2002

4 expansion plugs

One thing that plagues a Model T owner is checking their radiator for leaks.  I recently added a new outlet and inlet to the radiator, as the originals were corroded to the point of leaking persistently from rust pinholes.

After installing the new outlets, I needed a way to seal the outlets, fill the radiator, and check for leaks.

I went to the Tractor Supply Company (TSC) and found some expansion plugs.  They have many sizes, but these are the ones that fit the reproduction heavy brass inlet and outlet.

The photo at the left show the four plugs I purchased.

Bottom radiator outlet is 1 3/8 - 1 1/2"
Part# is 838637

Top radiator inlet is 1 3/4-1 7/8"
Part# is 838640

Two others I bought were

1 5/8-1 3/4
Part# 838639

1 1/2-1 5/8
Part# 838638

Cost was $2.99 per plug.

An additional plug could be modified by replacing the bolt with a metal schraeder air valve for pressure testing, and placed in the filler cap hole. Only a couple pounds of air should be used or you may create more leaks.


Next step was to insert the plugs and tighten the center bolt, expanding the plugs in the inlets.


Final step is to fill the radiator with water and check for leaks.


Many other projects and helpful hints may be found at the

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Inserting expansion plugs into outlets

Filling radiator with plugs in place