I have a 05 jeep grand Cherokee and it had been running hot so I changed the thermostat in it but it still goes in the red when it idles. Also when it idles and the heater is on it goes cold. Help pls

Make certain the rad fan comes on. Try switching on the A/C...this will turn on the electric fan. Check to see if it comes on when the A/C is on. If it doesn't come on....there is your problem. It won't run hot when you drive because the rad is getting the air flow thu it while you are moving.

And for the heat inside the cabin, sounds like you have air pockets in the cooling system that need to be bled out. Do this by leaving the radiator cap off, and run to operating temp. do not be revving it up or you will get a shower of coolant. The coolant may overflow from the radiator but that would be the air working its way out. Keep filling with coolant when the level goes down until full. Then put the cap back on the radiator before shutting it off.