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Kia Over Heating

Have a 03 Kia Optima with a 2.4L engine with 120K. The car recently started overheating occasionally mainly while stopped in traffic. Both fans are running and as soon as I get rolling, the temp gage goes down. I’ve noticed that it only happens while the trans is in gear. if I put it in neutral, the temp will drop to normal.

I replaced the thermostat and radiator cap thinking these may have been contributors. I also replaced the temp sensor because it controls both the gage & the cooling fan. Both fans operate with the a/c on but the single fan will not come on with a/c off. I tried another pcm from the salvage yard but still get the same operation. My next thought is to install a separate trans cooler to the radiator which is only 2 to 3 years old.

What could be causing this overheating & how can I fix it? When it does over heat, I usually turn the heater on full blast to help bring the temp down. Car is in great shape and would like to get it back to normal

Is there a thermoswitch mounted on the bottom of the radiator?
Many cars have one that also controls the (single) fan.

There is no thermoswitch on the radiator. I believe the fan operation is controlled by the pcm which is why I tried another one. I have also swapped relays for the fan to eliminate a bad relay.

The PCM gets its signal from a temperature sensor on the engine. It may not be the same one that you changed. That one may just drive the gage cluster. Ask the dealer’s parts guy. He’ll be able to look it up for you.

The diagram in the Haynes manual does not show a separate sensor. Also looking up on Rockauto for cooling fan controller, they have two types that you have to wire in with their own sensor bulbs. The overheating still happens with both fans running so there is something else causing this related to the car being in “D”.

I agree, if it’s overheating with both fans running there’s something else causing it.

My suggestion would be to start with a pressure test of the cooling system. A system that cannot hold its specified pressure (usually about 16psi) will boil over at normal operating temp. Even though you replaced the radiator cap, the pressure could be being lost through a leak somewhere else. A UV-sensitive dye kit can make a leak light up like a lantern.

You might also have a buildup of crud inside the radiator. An infrared thermometer can help with this, by using it to look for cold spots. Cold spots are caused by clogged tubes.

The water pump impellars might be eroded. A flow test can be run, but if you have a timing belt you’re going to want to change this when you do the belt anyway.

If you have a radiator that includes in it the tranny fluid cooler, there may be a breech between the cavities allowing contamination of the fluids AND compromising the ability of the engine cooling system to hold pressure. Typically this will cause muddying up of the coolant.

The last thing I can think of… you can do a chemical test of the coolant for presence of combustion byproducts. Presence of same suggests a breeched head gasket.

I strongly urge you to not add a separate tranny cooler until you’ve diagnosed the true cause of the problem definitively. You might end up causing more problems by covering up the original one.

Just went to do some recon… The cooling fan does come on but with the gage in the red and I got a temp of 180 with my infrared. The fan goes off when the temp drops about 5 degrees. I’m getting the readings from the same spot on the radiator. The gage seems to have a life of it’s own. I guess even though the reading on the gage is all over the place, it’s really not over heating. The stock thermostat is 180. The gage used to sit a little below the half way mark and never moved.

The timing belt and all associated parts along with the water pump were replaced about 8 thousand miles ago when I first got the car. I also replaced ALL the fluids and all the ignition components.

You have two fans. One for the radiator and the other for the A/C condenser. When the a/c is off this fan will be turned off as well. Perfectly normal, it is controlled by the a/c low pressure switch.

I suggest to flush the radiator and try again before going into more expensive attempts.

Both the radiator fan and condenser fan are controlled by the PCM from the signal it receives from the coolant temperature sensor.

These fans run at different speeds thru six different relays depending on the coolant temperature.

These relays are located in the under hood fuse/relay box. And are the following:

  • Condenser Fan Low Speed Relay
  • Cooling Fan Low Speed Relay
  • Cooling Fan High Speed Relay 1
  • Condenser Fan High Speed Relay 1
  • Cooling Fan High Speed Relay 2
  • Condenser Fan High Speed Relay 2

Here’s an example from RockAuto.,2003,optima,2.4l+l4,1434062,electrical-switch+&+relay,radiator+fan+relay,3060

In the fuse/relay box, there are two 20 amp fusible links. One is for the radiator high speed relays, and one is for condenser high speed relays.

Check if those fusible links are blown.