heater problem... possibly bad coolant flow?

[chillware]

Hi guys,

Ive got a 96 Grand Cherokee 6 cyl, ive noticed that in the past few weeks my heater is blowing cold air when I am at idle or low speed, also while im at idle the engine temp rises from ~210 to around 225-230ish, until i start going again then things seem to return to normal.. then another stop light and it gets cold again, pretty rapidly. I checked the coolent level today and the resivor was empty(!) so filled it, but problem remains.. will check level to see if there is a leak.. would a leak cause this to happen? The water pump is about a year old, so i hope thats not the cause.. any ideas?? thanks!

[Traktor]

As far as the engine temp goes, I would definitely replace the thermostat if it's doing that. It's easy to do yourself and is cheap. That wouldn't affect the heater coil tho. Weird.