My 2005 Optima 4 cylinder is indicating temperatures in the red. The temperature climbs rapidly into the red, and then the gauge indicates it cools into the noirmal range. It repeats this behavior continually. I've had the sender replaced. That corrected nothing. The vehicle is not actually heating as when the engine is turned off and restarted immediately, the temperature starts registering again from normal even if it was registering very hot when turned off. I've had it to two shops. Both agree that it's not actually heating up, but neither knows what's causing the false readings. Any ideas? FAB
2005 Optima false temperature reading
Jul 02, 2006
1 Replies
Greetings,
Generally speaking there are two possibilities. Even though you may not have a serious overheating probem, the possibility still exists that the gauge is correct and your actual temperature is bouncing around like you say it shows. If so, try some basic cooling system things first. All are cheap and relatively easy so it will not hurt anything if you do them.
First, check your coolant level in the bottle and in the radiator and top off as necessary. Second, replace the radiator cap. Third, replace the thermostat. And fourth, observe the function of your cooling fan (for possible malfunction of the thermostatic relay that turns it on and off or failure of the fan itself). What you describe sounds like it could be caused by a bad thermostat or a bad cooling fan.
The other thing to check for is to observe for any correlation between the spikes in your temperature and the AC compressor engaging. The AC adds a pretty significant heat load to the engine so watch to see if the temp gauge spikes when the compressor is engaged (it does not stay engaged 100% of the time even with the AC on Max).
If none of those do anything you are not out any real money except a few bucks for a new radiator cap and thermostat. The next thing is the gauge and you've already changed the sending unit so it could be a loose or dirty connector causing a bad electrical connection or possibly a bad or dirty ground. Electrical problems can be difficult to diagnose if it's caused by an intermittent connection or dirty ground wire. They invariably work well when it's in the shop but fail when nobody is around to see what is going on.
Good luck - Jonathan
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