Temperature gauge fluctuates

bad news if coolant not see on ground, garage floor
that means the engine is eating that for breakfast.

be more clear on coolant loss, now
level in rad next level drops each AM dead cold/?
that is serious.if yes, side tank okay.
1: not on ground
2: not in passenger foot well
3: not in oil pan, see chocolate milk look.
run enigine hot parked and with 15psi cap pressure now.... see
any leakes of AF seen now outside engine is it.

do engine compression test
spark tips nasty even same color as AF (green./pink, yellow )?
see oil or carbon dust in rad neck next cold AM test?
see steam at tail pipe engine fully hot? must not be so.
the only key fact is loss. word.
side tank (recovery) missing or broken tube or parts there)

If that bottom hose is cold, it sounds like the radiator itself is not circulating.

The thermostat "seals" the cool coolant giving up (rejecting) heat in the radiator & heater core from the hot coolant absorbing heat in the running engine "block".

When the coolant in the engine reaches a specific temperature (180 ~ 195 degrees) as determined by the value selected by manufacturer or when replaced, it opens and allows the hot coolant in the engine block to be pumped out to the radiatot & heater core for cooling and the cool coolant in the radiator / heater core is pumped into the engine block - replacing the hot coolant. The thermostat senses cool coolant in the engine block and seals shut until the temperature of the coolant in the engine block rises to 180 ~ 195 degrees again. This process continues over and over for as long as needed.

You should check to make sure that the coolant level in the reservoir / radiator is sufficient by checking when cold. Do NOT remove a radiator cap when it is hot! With the cap off, start the engine and add additional coolant as the engine warms up to normal operating temperature. If coolant levels are ok, the trouble could be related to the thermostat or possibly a faulty temperature sending switch. This means that the temperature of the coolant is fine - but the switch or sensor that converts the temperature to a voltage for the gauge on yur dashboard is the problem.

If the temperature is fluctuating up and down, you should have it fixed. Good luck!

Check out related help links with solutions to troubleshoot the problem:---
Click the link below:---
2004 Toyota Tundra: Oil Gauge and Temp Gauge Not Working?

http://howtobyme.blogspot.in/2012/05/2004-toyota-tundra-oil-gauge-and-temp.html

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Toyota 4Runner: Temperature Gauge Sensor http://technoanswers.blogspot.in/2012/04/toyota-4runner-temperature-gauge-sensor.html

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http://technoanswers.blogspot.com/2012/01/heater-blows-intermittently-and-temp.html
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Heat blows cold on drivers side and hot on passenger side? http://schematicsdiagram.blogspot.com/2011/12/heat-blows-cold-on-drivers-side-and-hot.html

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1992 Lexus LS400: Engine overheats, Antifreeze out of reservoir and heater Blows Cold Air? http://whatisbyme.blogspot.in/2012/05/1992-lexus-ls400-engine-overheats.html

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These details will help.
Thanks.

Watch the temp gauge when the electric radiator fans come on. The temp sensor that controls when the fan comes on may be faulty.

I would change the thermostat and if the gauge still acts up you may want to check the gauge, the fan is hooked up to a senor and will come on at a certain temp, usually when it gets hot. Hope this helped Tim

Sounds like you have an air;lock in your cooling system.Try placing a bleeder on the return hose to the heater core ........looks like a small tap

check your coolant level could have air pockets if level is not up where it should be.,it could make gauge fluctuate.

Here's the thing. The ECU will shut down AC if the engine temperature is too hot. If the coolant temperature sensor is malfunctioning (lying to the ECU) telling it that the temperature is hotter than it actually is, the computer will turn the AC OFF.

You need to pressure test the cooling system. If it holds pressure, I would look at replacing the water temp. sensor. If it doesn't hold pressure, you have a coolant leak going on. If you don't see it dripping on the ground or inside the car, I would be suspecting head gasket problem.