In “flicking” through the debate to date, I may have missed the following understanding of gauges & senders, as used in small aircraft;
None can be relied on to give an accurate (as in scientific standard) reading. They are at best an indicator of system “health”/problems.
All pilot/owners of small aircraft should, in my view, regularly log the readings of their various pressure/temperature reporting systems, along with OAT, altitude, air speed and engine RPM.
Care should be taken to try and standardise the environment when these reading are taken eg always at cruise power, at RPM ?, altitude?, similar load (2 PAX , full fuel, etc)
This will give them historic of readings, that they can refer back to/compare for any significant changes (departures from the norm). The norm may be an unusually high/low reading however if 'master" gauges have been consulted/used to ascertain system health & all OK, then it is this position of the indicator that is important, not the numbers.
Any reading that departs from the norm (taking into account external factors like altitude/OAT, etc) should be investigated.
Note:
All sensors/senders will lose efficacy over time (hrs of operation), as will gauges (usually at a slower rate).
It seems to be part of our human nature, that any abnormal reading is immediately assumed to be an engine failure in the making (your training should have included cross checking readings eg comparing oil temp with pressure) with a corresponding high repair/replacement bill. More often than not it is some relatively low cost easy fix - try opting for the cheap fix first, it may just pay of.