Re: help please
The rear heater core is probably the most remote part of the coolant circuit. It can easily get air bound, it's where deposits are likely to settle out, and it will be the first place that will indicate that your pump is getting worn. Any one of these conditions will cause the return hose to be much cooler than the supply, if this is the case, you've got a flow issue. If both pipes are cold, you've probably got complete blockage.
Prius repellant, just add gas.