Technical Adding a temp gauge.

I want to add a temp gauge to my 239 flathead. I have the stock sending units but want to add a mechanical gauge. This what I have


This the gauge


I know I need an adapter for the gauge to fit the flathead, any ideas


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Take the plug in the head and the temp gauge to NAPA and have them find the correct adapter to put the two together.

 

The mechanical gauge thread is probably 3/8 or 1/2 NPT, whereas the senders are 1/4 NPT. You may be able to find adapters, but will they allow the mechanical gauge bulb end to pass into the cooling system. It must be immersed in the coolant to get a proper reading. You may have to drill out the OEM sender unit threaded hole and retap for the mechanical gauge.

It might be easier to find an adapter that clamps to the top radiator hose and is threaded. I remember having one supplied with a mechanical gauge years ago.

 

Mechanical gauge is not pipe thread. It seats in the bottom of the adapter to seal.

 

The head holes do look too small to be able to use the 1/2 NPT "temp gauge adapter".

If it is too small, like 3/8 NPT , and if you did not want to drill/retap to 1/2 NPT, maybe the radiator hose suggestion may be easiest......if it has the metal pipe for the upper hoses?

If it does have pipes, you could silver solder the special temp adapter with the sealing seat, into one of the pipes

There were also pipe threaded "thingy" that you punch a round hole in a rubber rad hose, and this part gets held to the hose with curved plates and a nut. They were for heater hoses, but I never looked for one online. They may have been the 1/2 NPT threads, not sure though.

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Yup needs the adapter that comes with the gauge, then you can adapt to the hole size. Will the bulb even go inside the threaded hole in the head, if not you might have to go to an electric gauge. If you do go electric get an old (60's-70s) made in the USA Stewart Warner or something similar.

 

Just went thru this last week myself.Installing a Classic Instrument gauge in my 239 flatty.I knew I had it wired correctly but it would not work.I changed the sending unit but it still didnt work.The temp sender that came with the guage was way shorter than the stock sender so I didnt use it.Mistake.That was the fix.I guess it gets enough coolant to make it work.I didnt need an adapter for the Classic sender.