Typically if your gauge doesn't move or stays cold when engine is warm or hot when the engine is first started then you have a bad sending unit. There are circumstances where a gauge may fluctuate from hot to cold under normal running conditions, this could indicate a sending unit starting to fail or bad connection. This is a low cost item if you have any doubt
replace as the internal damage or complete engine replacement is much more costly.
To fix the temp gauge check the temp sending unit first. A bad sending unit is a common problem with the temp system.
The temp sending unit or gauge is bad, probably the sending unit.
bad relay or temp sending unit
If it is not overheating then the temp gage or the sending unit are bad.
more then likely it could be the temp, sending unit. or a bad wire to temp, sensor!!
First try unplugging the coolant temp. sending unit and plugging it back in(may just be bad connection at the plug), next replace the temp. sending unit if the plug-in thing didn't work.
Replacing the gauge could be a costly job but it is seldom the gauge goes bad. More likely the temp gauge sending unit is at fault. Replacing the temp gauge sending unit would take less than 15 minutes.
cooling fan relay has gone bad or coolant temp sending unit is bad
Temp sending unit for ecm. most likely sensor is bad computer cant read engine temp, fast idle do to cold reading
Could be, low on coolant (a leak in the system), a stuck closed thermostat, a faulty temp gauge sending unit, a bad head gasket or cracked head (worst case scenario).
Yes, it can leak at the sending unit.
the oil pressure drops when i turn on the a/c is this because of a bad oil sending unit?