Temp gauge shooting up very quickly

[jumpkickyergunt]

I've recently replaced the water pump, checked coolant, replaced several t stats. I can see that the coolant is circulating and there's no bubbles or oil in the coolant. What could this be? When I took off from a stop sign today the gauge shot up way past the H out of nowhere. I'd think that it would have popped the radiator or boiled over if this thing was reading accurate.

[fxrsrider]

at running temp, you can put a thermostat wire in between the radiator fins near the return side of the radiator.  Compare the temp reading that you get manually from the temp that your gauge is reading.  This will help troubleshoot if the gauge or sensor are faulty or not.  (I use the thermostat feature from my Klein Tools MM200 multimeter).

Your truck's thermostat (not same as referred to above) may be stuck closed (i.e. bad).

You may want to back-flush the whole cooling system (which is generally good routine maintenance).

[FlatBlack77]

the gauge/sending unit could be bad. is it a factory gauge?

[jumpkickyergunt]

It is a factory gauge. I haven't done the sending unit yet.

[Irish_Alley]

TEST PROCEDURE - SENDING UNITS

The subsequent charts provide precise sender resistance values for three specific gauge readings (Low, Medium, and High), hence, can be used to estimate sender resistance when actual physical parameters are known (e.g., engine temperature that is verified with a thermometer, actual fuel tank level, engine oil pressure that is verified with a manual gauge, etc).  Therefore, a sending unit’s resistance can be measured and “subjectively” compared to its interpolated value between ‘Low,’ ‘Medium’ and ‘High,’ based on the charts and the observable/verifiable physical conditions that actually exist on the vehicle.


COOLANT TEMPERATURE GAUGE PARAMETERS

For Truck Years:  1967 - 1973

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 76 Ω
Right Line (Hot) when sender resistance = 51 Ω

For Truck Years:  1974 - 1978

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 350 Ω
Middle Line when sender resistance = 68 Ω
Right Line (Hot) when sender resistance = 46 Ω

For Truck Years:  1979 - 1990

The Temp Gauge Needle Should Point to:
Left Line (Cold) when sender resistance = 1,365 Ω
Middle Line when sender resistance = 96 Ω
Right Line (Hot) when sender resistance = 55 Ω

[Irish_Alley]

now you can use the same numbers to test the Ω of the sensor. if you have the truck running you should be able to watch the Ω drop as the truck warms up.

[jumpkickyergunt]

The ohms read at 30 when the needle was in the center. Also, the gauge stopped shooting up past H and has been somewhat steady recently. The wire was poorly routed and might have been too close to some of the exhaust pipes. After I rerouted its been decent, but I don't think its accurate either way.

[Irish_Alley]

i would get a new one sensor to compare the readings to. put it in pot of water get a base line reading then turn the heat up once the water boils youre at 212 @sea level