Needle Is Too High On Temp Gauge

[inline6]

I found information pertaining to this issue on this site and on Zhome.com.  However, rather than bringing back a thread last contributed to in 2013, I will start a new one and hope I can fix the problem I am having.  

The Needle on my temperature gauge is definitely going to high.  I know however, the engine is not overheating because I have checked it with a laser temperature gun.  Here is the info I have so far regarding the problem. 

When I first bought the car, I got the engine running for a brief amount of time before taking the engine out for rebuilding.  I ran it up to temp in my garage (car was inoperative) and noted that the needle on the temp gauge was a bit high.  Here is a slightly blurry screenshot from a video I took at the time.  The engine was fully warmed up:



Fast forward about six and half years and with the car fully restored, the same temperature sender put the needle (same gauge) on the base of the last stroke of the "M" of TEMP.  That is not all that far away from the red zone of the gauge - near the "250".  So, I figured to fix this, I would just need to buy a new temperature sender.  When I changed to the new one, an aftermarket unit, I saw essentially the same thing, but the needle goes to the left side of the "P".  

I read in one forum thread that buying an OEM temperature sender fixed the issue.  That seemed pretty promising.  So, I sourced an original "Sankei" sender from a seller on Ebay.  I switched to that one... and again found the needle goes to the left side of the "P".  

As I have continued to look for information about solving this problem, I have come across this article on Zhome.com which was referenced in an old thread on this site: 

In the Zhome.com article, there is mention of "adjusting the voltage regulator".  From the context in the write up, it seems this is a different voltage regulator than the one for the alternator.  Instead, this seems to be something, perhaps inside the gauge itself.  However, the author is working with a 280ZX, so I am uncertain of the applicability of the information to my 1971 gauge.  

I did consult with @SteveJ back in November about using a "pot" like this person described in their post in the first of the mentioned threads above.  I purchased this one per his recommendation:
https://www.mouser.com/ProductDetail/BI-Technologies-TT-Electronics/93PR50LF?qs=UjOdgN%2FjCTVtZlza%2Bf%2Fo7g%3D%3D

So, that is what I have so far.  My plan is to check the three temperature senders that I have for differences if any, compare them to the specs provided in the Zhome article, to learn anything relevant about the voltage regulator and try to adjust it if possible, or to wire in the "pot" to ultimately resolve this issue if that is what it comes to.

 

Edited Friday at 03:16 AM by inline6

[Yarb]

Why not try to find a known good gauge that someone possibly here on the forum for testing purposes. It won’t go to waste having an extra for future use. If it doesn’t pan out.

[Captain Obvious]

First, have a look at this thread that details how the gauges work:

[Captain Obvious]

Then, in this pic... You see the little screw? That's an adjustment screw for the gauge. Make the contacts tighter, it should read higher. Make the contacts looser, it should read lower: