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I installed an AutoMeter mechanical water temp gauge on my V10. My gauge is calibrated from 120 to 250 degrees. You can click on my web page at the bottom of this post to see some pix of the gauge in my truck. There is also a link to Stan Wright's web page where there are detailed installation instructions.
The highest temp that I have witnessed thus far is 210 degrees. This was pulling a 30' travel trailer through the mountains of North Carolina in the early fall. I would think a gauge with a max of 250 degrees should be more than adequate.