Low Temperature Reading

[John King]

I have a 1990 Mercruiser 3.0L.  Several weeks ago the engine temperature dropped from its normal 150 deg plus to 120 deg.  I have changed both the thermostat and the temperature sending unit, but still have a temperature of 120 deg.  Please help.

[Ken Juul]

Temp guages normally sense a change in resistance to determine temperature.  Normal electric troubleshooting techniques.  Check for clean tight terminals, correct voltage, no cracked wires and good grounds.  If that all checks out the only thing left is the guage.

[Ray & Sandy Erps]

Quite a few digital volt meters have an accessory that plugs in and takes the temperature of the surface you hold it against.  Might be able to hold it against a water jacket to confirm whether the engine temp is low or not.