MG Car Repair: Temp Gauge, upper radiator hose, gauge reading

Question
When I crank the my 73 MGB the temp gauge goes all the way to hot with in a couple minutes.  I replaced the unit in the motor and the gauge but not sure what I may have done wrong.

Thanks,

Mike

Answer
Hi Mike,
You need to do several things first and most importen do a preliminary test. Feel the upper radiator hose when the engine is cold and start it up and keep feeling the upper hose as it warms up and note the temp gauge. If the hose seems to represent what the gauge is showing put a meat thermometer into the coolant when it shows hot. Be careful opening the cap as if it is really that hot it will boil the coolant out the top.

If however, the gauge shows hot and the upper hose feels cold then you need to replace the thermostat.

If the hose and the gauge seem to confirm each other then you need to either get the test dye from any auto parts store and test for CO in the coolant. Or take the car to a shop that can sniff the radiator for CO. (not all shops will do that)

If the meat thermometer says it is not hot and the gauge says it is, then turn the key on and look at the gauge reading and remove the wire off of the sending unit and note the gauge (needle should deflect all the way in one direction) then ground the wire and the gauge should deflect all the way in the opposite direction. Also look at the fuel gauge and note if it is reading correctly. If not replace the gauge power stabilizer and retest the temp gauge.

Howard