was that reading at a hot or cold engine temperature ?
if cold, it will go down when warmed up.
if that reading was when warmed up, what did it go to when, at say, 2500, 3500, 4000 rpm ?
if your bypass valve is stuck closed, you would have blown off the oil filter long ago.
you need to temporarily hook up the mechanical gauge where you can see it from cold start up to warmed up going down the road, then hot idle.
the gauge you have now is most likely ok.
you can do this now while you are waiting for the correct [1/8" NPT ?] sending unit.