When I'm driving the coolant needle stays in the middle. No Issues.

When I start to idle at a Traffic Light the Coolant Needle Starts to Rise Towards Hot.

Both the Radiator Fans are working fine. What could be causing this issue?

 

Sticking thermostat, faulty fan switch, blockage somewhere in the cooling system. Stop driving the car and find the issue or you will lose a coolant seal.

 

That's exactly what I've done. Stopped driving the car. Dont want to loose the engine.

 

Does your car leak coolant ever when you stop? How old is your waterpump? (check the weep hole for any drips). Stock or aftermarket radiator? Are the fans both operating correctly? After that I'd pressure test the system, then pull the thermostat. Do you notice "champagne bubbles" in the filler neck (cap without the spring). AST? There are so many possibilities, but that's where I would start.

 

im not guru like the others but my theory (given everything is in good order and the previous owner didnt ghetto rig stuff) bad belt or not enough tension would be my guess

when u spin the main pulley does your water pump pulley spin as well/freely? double check the tension on your belt.

idle=low rpms, pulley is slipping and not cooling = over heat
running= higher rpms, still slipping but since its moving faster it is getting a little better contact. although its in the "middle" im assuming its the stock gauge and the middle has a range of 87-10x?= so in theory it could be running hotter than normal, still within "normal" range but not hot enough to be over heating (yet). if you had a power fc and commander or a after market gauge that gave a more accurate reading would help narrow this problem down..

just my .02

 

My car did this, come to find out one fan had come off the fan motor.

 

does the coolant buzzer light ever come on?
if not, check the usual places, fans, thermostat and water pump
oh, make sure belts are not slipping
also, I hope you are not running just plain water

 

How do you check to see if your belts are slipping

 

Check the belt tension, specs are in the FSM. Are you using under drive pulleys and/or did an air pump delete?

I'd skip straight to doing a coolant pressure test and let it run overnight, it's the best way to know if you have a coolant leak.

I didn't see anyone mention the rad/AST caps...those can cause problems too.

You could be overheating even while driving, the stock gauge is more than useless. Do you have a PFC or any other way of semi-accurately checking your water temps?