In the USA, '90-'94 Miatas had the "real" oil pressure gauge, and '95+ had the "idiot" gauge...
I've seen nothing to suggest that the same change didnt happen at the same time for other markets (ie, NZ-new and Japanese imports).
The water temperature gauge is deffinitely NOT an on-off type operation...
It is non-linear. It has a "dead-spot" where its reading doesnt change....
When it reads low, your engine hasnt warmed up.
When it reads high, you need to do something (like stop the engine).
When it reads near the middle of its range, then its warmed up, but not dangerously hot, and its had its internals tweaked so that a RANGE of normal temps actually give the same static reading.
Some would prefer a more linear action, but this non-linear approach has its reasons, and is not completely stupid.
From experimentation, I can tell you...
the needle will stay pegged on cold below about 45 deg C
the needle will be up to normal by about 70-75 deg C
the needle will start to rise above normal at about 110 deg C.
I havent let my engine get hot enough to know how hot a full-scale reading is?
Fletch.
Red '90. Many n/a mods and Link ECU