05 Aztek Overheats @ Idle/Stop

[grp3dradis]

I have a 2005 Aztek that runs great at constant speeds but starts to run very hot at idle and at stop lights. It cools off again after I'm back in motion. Having the AC will slow down the amount of time it takes for the engine to run hot at a stop but not enough to keep it from over heating.

I have replaced the radiator, thermostat, temperature sensor and water pump. I've verified I do not have any coolant leaks and no smoke coming out the tail pipes.

The radiator fans do come on however they don't seem to run any faster than they do at normal temp with the AC running (not sure if they are dual stage or not on this car).

To make it more interesting: if I put the car in neutral and keep it revved above 2700 RPM it will cool back down while still sitting still.

To make it even more interesting: I don't get any heat in the cabin unless I'm in motion or have the engine revved up. Once it's at idle RPM the cabin air cools down to ambient.

I'm leaning towards a blocked heater core or something to do with the fans not kicking in soon enough or kicking into high speed.

Does the Aztek have a fan control module or is it just the wiring from the fans into the fuse box and the corresponding relays?

I'm also curious what the experts on this forum think of the situation. Any advise before I give up fixing it myself and take it to the shop?

 

[EaOutlaw]

Hi it sounds like you have air trapped in the cooling system.

If the replacement thermostat didn't have a small jiggle Pin built into the body of the thermostat, I would buy one that had this feature.

This way you know before you start it that once you opened up the air bleed screw and purged the air that you got all of it out.

People tend to bleed off the cooling system while cold forgetting that the thermostat has not opened releasing a large pocket of air. this is why it is important to have this small opening in the thermostat housing.

also when the thermostat is out it is best to top off the block with coolant mixture to just below the thermostat so you know there is no air in the block.

Test this theory by squeezing the lower radiator hose the level should go up without causing air bubble to come out.

For a thermostat to operate correctly there has to be coolant contacting the thermostat if air is trapped in the coolant system from a service, changing the radiator etc you can burn up your engine waiting on the thermostat to open.

when ever possible use a factory thermostat or Stant brand which ever has a Jiggle pin or built in air relief.

From the Stant website.

WHAT DOES A JIGGLE PIN DO?
It helps bleed the cooling system of trapped air by allowing air to pass into the radiator and released from the system.

MY THERMOSTAT HAS A JIGGLE PIN BUT THE STANT THERMOSTAT DOESN'T. WILL A STANT THERMOSTAT STILL WORK?

Yes. Many thermostats have a “jiggle pin” that allows trapped air in the cooling system to pass through the thermostat and be released from the system. Some Stant thermostat do not use have a jiggle pin. These thermostats will have a "bleed notch” or other method of removing air from the system.

Once you have the block filled with the coolant mixture to just below the thermostat sealing surface, install a properly vented thermostat of your choice.

Reassemble the cooling system. finish topping off the cooling system with the proper mixture, purging the rest of the air using the bleed screw normally on or near the thermostat housing until you get a steady stream of coolant flowing from it.

Some vehicles have more than one bleed screw so check your owners manual.

Once the cooling system is completely topped off squeeze the upper and lower radiator hoses while watching the coolant level in the surge tank, the level should go up when squeezed in and down when you release the hose.

if you see air bubbles in the tank when you do this try purging the air again from the air bleed screw.

Good luck I hope this information proves useful.