Heater 'growling' when engine is stopped

There is some confusion on this matter because in the US, and the north American continent the Prius is fitted with three pumps, a thermos tank, and a coolant control valve.
This does not apply to the rest of the world where the engine coolant circuit has one mechanical pump, "engine driven" and one electric pump for when the engine is not running to supply the heater core. There is no control valve or thermos tank. The OP lives in the UK meaning his car has the simpler system.

John (Britprius)

 

Just as with any other car there is just the normal thermostat. The electric pump is there to feed the heater core with hot coolant when the engine is not running.
The growling noise is almost certainly air trapped in the heater core, due to the coolant level getting low, and quite possibly this is aggravated by the leaky pump allowing more air in to the system as the air already in there contracts as it cools forming a vacuum.
With the VCI it is possible to run the engine continuously to help remove the air. This can also be done by putting the car in service mode.
A vacuum pump fitted to the top of the rad helps a great deal to remove trapped air, but if the engine pump seal is weak you may just draw in more air.

John (Britprius)

 

My heater pump made a slight rattling noise -- I identified it by scrolling the cabin temp up and down when at a stop with the engine off-- before it finally failed, was a pain to change. If you are getting decent cabin heat with the ICE running, I would lean to a failing heater pump.

 

The electric pumps make a growling noise as they fail. I don't think it is air in the system if the reservoir still has some coolant inside.
Un plug the electric pump and see what happens. It will throw a check engine light but that can be cleared with a code reader which you may already own.

 

The pump for the heater is behind and a bit underneath the inverter next to the engine bulkhead. I replaced it when I replaced my brake actuator. I'm not sure if the inverter has to be moved to change it, but it sure helps. You could try first taking out the inverter mounting bolts to give an inch of two movement forward for more access for the pump. The engine cowl definitely needs to be taken out, not as bad as the dashboard.
Engine Compartment Cowl Removal: Owners w/Mice or Stinky AC take note... | PriusChat

 

Moving the inverter is not as bad as it sounds. It is easy to unbolt. All the coolant hoses and wires going into it are flexible so you can push it over a few inches without committing to a long complex procedure. The inverter is not live as long as the car is off and has been off for at least a minute or two. Removing the service connector is a good precaution as well.

 

OP said that the coolant level was around 1" low at the radiator neck. That is evidence that air is getting in the system. If the system was air tight, the overflow container and radiator cap would keep the radiator itself totally full.

 

I just don't see how a slow coolant leak is going to make the electric pump growl. I've never seen aerated coolant only power steering fluid. Has anyone seen coolant frothed up because of a leak or any other reason? It just leaks out and eventually overheats your motor once it goes too low. He probably needs both mechanical and electric pumps replaced to get the car back into shape. The mechanical pump will be much more challenging to change and requires some finesse to get right.

 

Sorry to hear that Richard. Are you sure you got it from the program? as I have not come across anyone else that has had a problem with a virus from the program. Word would get round very quickly if there were problems.
If you need a copy let me know and I will see if I can Email you a clean copy.

John (Britprius)

 

I had a question about the heater and I'd sure appreciate any input anyone may have.

I never understood why the engine idles when providing heat, without actually charging the battery.
I mean, I'm stopped at a drive-thru, it's like 5 degrees outside, and my battery is in the blue w./ 6 bars.
Since the engine has to run anyways to bring the cabin temp up to whatever I set it at (70-75), why doesn't the engine act like a generator at the same time to charge up the battery to 8 bars green? How can it possibly be less efficient not to? I mean you'd think the extra gas used would be more than saved once I start moving again?

Am I missing something?

Thanks,