Just in case you did not know, there are some late model small sixes that have a larger NPT thread boss in the thermostat neck that may work for you.
Do you know what model and year? It makes a good place for an aftermarket temp sender/gauge addition

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This is the system she was referring to:
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My van's 200 has the T-stat housing with the threaded port. I was going to use it for a temp gauge, but it's downstream of the thermostat.
For a cooling fan, that's probably true. It will function fine for that. I had forgotten my jeep is set up exactly like this and works well!This is my first deep dive into the subject but my thought is that it shouldn't matter where it is as long as the turn on and turn off temps are higher than that of the thermostat temperature rating.
Similar situation on one truck- a "temporary" loss of auto-on fan switch was not that big a deal this past summer. Manual on in town, not needed at all over 35mph. Still gong to redo the auto switch, but not urgent.Ok, it's settled, I'm moving onto tapping the C9DE thermostat housing. The 1/4" 18 NPT is on it's way and I've already got my 7/16" pilot bit. I'll tap it and install the 185/175 sensor that came with the fan. I may wait until I install the C9DE before I put it into the mix as I don't really want to do the job twice. In the meantime, I have my manual override switch and I can just leave it on and the fan is on whenever the car is running. If I'm travelling any distance, I don't even need the radiator fan on because the car runs cool anyway, especially in this cool fall weather.
“...onto tapping the C9DE thermostat housing..."
some already done if interested, no?
Remember you can always tap more if too tight, but it is hard to put the material back on if too loose.Thanks @chad. I appreciate it. I've drilled the pilot and and will tap it tomorrow. I'll send you an emergency sos if I bugger up the threads![]()
U go bro! I buy to save time. (“...already done...”)Thanks... I'll send you an emergency sos if I bugger up the threads![]()