Latley when i park my car and let it keep running, i hop back in and see the temp guage is almost in the red. But it only happens when i have the heat off. When i turn the heater on, the gauge instantly drops back to normal

I need to flush my heater core because i don't have much for heat. Could this be a possible cause?

Any suggestions? Thanks in advance

 

The sensor may not be working that kicks the fans on. They automatically come one when you turn on the heat/AC, thats why it cools down. There are also three relays in the fuse box under the hood. The first 2 are for the left fan and the right fan, and the third one turns on the fans when you turn on the heat.

 

There is really not a sensor that turns the fans on. The pcm controls the fans based on the temp sensor in the water pump input and from other input such as the mode settings on the HVAC control. You might need to use a scan tool and check the reading that the pcm is getting from the water pump sensor.

If you are merely turning on the heater, the fans don't come on. They will come on if you turn it to any mode that engages the a/c compressor (that includes defrost). Possibly your heater is just dissipating the heat, but since you said little heat comes out, that may not be the case.

As far as the fan relays go, low speed is accomplished with relays 1 and 2 and high speed with the additional engagment of relay 3.

 

you could have air in yoru system. Have you done anythng that required drainign some coolant?? That will cause pockets, and make your temp go up. I'm not realy sure if your symtoms go along wiht this, but its jsut another thought.