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Temperature gauge hot

hyundai elantra 1999 temp gauge reading hot, No leaks anywhere, coolant full no running over into the overflow tank. Oil level is good. When driving temp reads normal when you stop at lights temp goes up. can you help me?

Can you hear the radiator cooling fan running when the temperature goes up? If you turn on the A/C when the temp is going up does the temperature stabilize and/or go down. I am thinking your radiator fan(s) may not be working.

Sounds like the radiator fan(s) are not coming on. This could be a fuse, a relay, or a bad coolant temperature sensor in the radiator.

I agree with Researcher and McP that it osunds like the fan isn;t coming on when it should. That could be either the fan itself or the temp sensor for it.

But there are other possibilities on a 10 year old vehicle, so post back if it turns out that the fan is operating properly.

The fan is working. Checked it out today. Before the temp started going up the needle on the gauge was jumping around but stayed in the normal range.

Could also be a clogged up radiator. I had a similar situation. Flow test on the radiator showed 40% flow rate than normal. Ultrasonic bath couldn’t clear it, so I bought a new one. Fixed the problem.

I am having a similar problem with my Hyundai Sonata 2005 and have posted on this
site and have been getting suggestions re: fan radiator, sensor, internal leak,
thermostat, etc. etc I have seen this overheating in my own car when I am stuck
in beltway bumper to bumper traffic. The only thing that STOPS it is turning up
the HEAT full blast and/or stopping/turning off the car. It happens randomly too
out of nowhere in town.

Possible sticking t-stat.