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I have an aluminum koyorad in the car right now. I emailed Koyorad to verify and it has a 1/8 PT fitting in it. I CANNOT find a temperature switch in that size; I can only find NPT. I did find an adapter, but it says I would need a test port sensor extender with it? I've also read NPT will thread into PT, any truth to this?


Does anyone know of an option other than those huge wire mess sensors that push into the radiator? I'm trying to clean the engine bay up.

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It Is 1/8" NPT which is SAE National Pipe Thread, an USA thread size.  and you will not find a 1/8 NPT Temp switch, at least I have not been able to find one.


What I have use the past is Male adapter in brass that is 1/8" MNPT x 3/8" FNPT.  Then by a 3/8" NPT Sender.










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What ever you do, don't buy Summit (or any other speed shop's) house brand switch.

Was being a tight wad, and bought a Summit house brand switch, and it failed within a week.

Buy from a known cooling fan manufacture, you will get a better product.


Go find an aluminum 1/8 pipe plug (McMaster-Carr has them.

Drill & tap a 6/32 hole into the center, and use one of these:



It will screw into the taped pipe plug.


Remember, always use a rely, and it should be twice the amp rating of the fan(s).

Inrush current of repeated cycles will kill a fan relay that is only rated at what the running amperage of the fan.

Been down that road....

A 30 amp fan, should have a 70-80 amp relay.

And make sure to use a decent size wire gauge.

Many kits are made with the cheapest wire/relays/connectors that they can get away with.

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Thanks guys.  I ended up just going with a 1/8 NPT switch and then got an 1/8 PT adapter.  Koyorad was adamant in their response it was NOT NPT and was PT.  It won't look as clean, but it'll work in the interim.  I'm just trying to remove all the relays/wiring/battery from the engine bay and was going to go with twin electric fans at the same time. 

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