Temp gauge keeps bouncing around making the fan stay on

I would try to drive it home. What's the temp before it drops? Might just be a bad sensor. Do you have an electric read out? Mine does and the gauge has it's own sensor, so you could double check temp on the electric read out.

 

WHAT engine? is it throwing any codes? it's sounds electrical. like a sensor wire grounding out. if it is a detroit, high coolant temp, or low coolant will give engine warning & shut down. your not in bad shape(yet) if just the warning light comes on & not the engine shut down light. if a detroit, there is a sensor at the thermostat housing that sends the signal to the dash gauge. there is also a sensor in the passenger side head that read coolant temp & it sends signal to e.c.m. this is on older models though, not sure off newer ones. is the engine fan coming on? can you read the codes? do you know how to read the codes? with truck off turn key in forward on position, but do not start. hit your override switch on dash & write the the number of flashes, example : 3 red flashes followed by a pause with 4 red flashes would be code 34 this will be very helpful in diagnosing your problem. i.m.o. as long as your engine is not running hot, you should be safe driving. good luck. I wish I could be of more help.

 

If you can find an AutoZone in the area, purchase part number 254. It's a pigtail made by AutoZone/Duralast with a few inches of wire attached. Cut off your current coolant temperature sensor pigtail about the same length as the new one, and splice it in. It costs about 12 bucks instead of buying a whole new engine wiring harness.

 

You might check your air bleed hose that runs from the top of the engine to the coolant tank. If it gets restricted in any way air can accumulate in the topside of the engine and cause the temp sender to send false/erratic signals to the guage.

 

Code 46 on a ddeck 3 is sensoe supply voltage low, e.c.m. battery voltage low, if your batteries are good. your problem may be between the sensor & it's wires.

 

Wondering if he ever found what the problem was...mine's doing the same thing