If you installed an aftermarket temperature gauge, where did you tap into the engine? Pix would be great, thanks.

Some you might be able to use a block drain, those are 1/4 npt.
I don't know when they moved but I couldn't on my 01 Durango they moved the block drain back, conveniently the starter is smack dab in the way.
On my Durango I took the heater hose nipple out, put a pipe nipple on there to raise it above the beer barrel manifold, put a "t" on the end of the nipple and put the original heater hose nipple in one leg and the temp gauge bulb in the other side of the tee

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What year magnum? The pre 97(i believe) have two ports for temp sensors. One for the pcm and the other for the gauge. If you have the later magnum you can use the earlier intake and have a port for the sensor. Or dill out/tap where the sensor would be on the newer ones. In the pic below you can see the port to the right of the water neck.

[img]https://www.forabodiesonly.com/mopar/attachments/dscn2602-jpg.1714624222/[/img]