Prius heater not getting hot enough!

First- just for reference: It's a Coolant Reservoir. There is no gas to 'degas' in the coolant.

Second- if the radiator is clogged with 'leak-stop' , you can bet the heater core is also full of that crud.
You might have some luck back flushing just the heater core hoses with the vinegar solution, but try to monitor the amount of pressure your using with your garden hose. 15psi is typical for cooling systems. You might be able to use 20psi on the heater loop.
While you're tooled up to do this 'back flush work', you might as well get it set up to flush the radiator also. Could save you the work of replacing it, or not. You might find you have minimal flow through both units. ,,, Sorry.

 

If it's not flowing INTO the radiator, you have a blockage.
Take the upper hose off and see if the passage on the block is blocked.
Did you look at the ports behind the coolant pump? Maybe they are blocked.
And look into the radiator, you'll likely see it all clogged.

Seems like you ruled out the thermostat and coolant pump. A clog is the only
other option.

 

Another job for a cheap borescope!

If you had both hoses disconnected from the block you could try the ol' Lip Lock method of 'feeling' if it's clogged or flowing.

Or try to get flow to go through it from a garden hose.

 

If coolant is being released out of the overflow on the reservoir (degas tank), the engine is overheating. I say you still have a problem with the water pump working properly. Start by monitoring the coolant temperature. See post #23.

 

With the larger hoses off the radiator, block the lower hose fitting.
Then you could fill the radiator, then remove the lower hose fitting. The water should
dump out pretty fast.
Then try to use the hose to clear out every passage you can.

When you fill it back up. Fill very, very slowly, a small account at a time. It will take a while,
but by pouring slowly, the coolant will be able to push out the air. Fill to the B line on the tank.

 

Whats the story on The Late Model JDM engines?

 

The story is Toyota made the Prius v/+/alpha for European and Asian markets through 2021. Since JDM engines are from Japan there is a chance some of them could be 3 years old. Of course they don't put them through the miles or loads we do so those gen3 engines are probably as good or bad as a 2016/17 US Prius v engine when they were three years old, generally excellent with no obvious problems or oil burning. By then Toyota had updated gen3 head gaskets, intakes, egr valves, brake boosters, inverters and ecm software.

 

Even the cheap water pump knockoffs last more than 20 miles. Probably closer to 20,000 miles.

Hopefully the thermostat is working. If it was failed closed you would never get flow through the coolant reservoir.

The T hose is on the output of the heater. It feeds the egr cooler and exhaust heat recirculating system.

I imagine you get a lot of flow through the reservoir tank once the thermostat opens. Those two reservoir hoses and the coolant reservoir bypass the radiator.

So you could have a blocked heater, blocked radiator and or continuous "air" being pushed into the coolant system by a bad head gasket leak.