Prius heater not getting hot enough!

How did the coolant look? Again, a recent third Gen acquisition, with those miles, I’d suspect cooling system clogged with stop-leak product, to mask head gasket failure.

 

Perhaps you didn't get all the stop leak out of the radiator????
If the coolant pump IS working, and the thermostat IS working, then there
must be a clog somewhere.
Are you talking about the HEATER hoses? Or the RADIATOR hose?

Maybe the flap is not opening to allow air to pass over the heater core?

 

Get an OBD2 scan tool and monitor the engine coolant temperature.

 

This is where you get screwed around when you don't tell people where you are 10 minutes of driving and -30° weather or 10 minutes of driving in 48° weather makes a big difference in you know 30° weather freezing or less it's going to take a couple minutes for all that to warm up the pipes the hoses etc It's very tricky You will need to get the three manual set or the big PDF for this car and look at the troubleshooting section for the heat It is lengthy thermostats usually not anything to do with it I have Prius with original kuze or whatever the brand is thermostats and I'm sitting right out in the yard now working fine I changed one in another type of Prius the other day thinking the same thing made no difference what it usually is is the coolant is not able to move around the system because there's a big air bubble in place so you can't get heat I know it sounds silly but this is what's happening generally if you take your radiator cap off get the car to run and maintenance mode or usually if you have a call for heat the heat turned all the way up the engine won't shut off until it gets to temperature My car's been shutting off when it's very cold outside first thing in the morning with a call for heat and heat set to high because inside of the engine and wherever something is near those sensors is getting hot and then there's an air bubble and nothing's moving so I've got heat somewhere in the engine and the related business but it can't get to the heater core because there's too much air so it is really tricky to get all the air out but you have an electric pump you can call up and all of that which can help you somewhat they also make a special tool that lets you drop 1.6 gallons of coolant as fast as you can pour it out of the container and helps evacuate the air others here have the tool and they'll show you a picture and a gen 3 honestly I've never had this problem and generation two this is very common.

 

What was the miles when the head gasket was replaced? Was the EGR system (including intake manifold) also cleaned, thoroughly?

 

So of course I guess what did you empty the system and then fill it to the b line and then drive it until it went to the full mark or none of this is happening usually I thought on the generation 3 the few times that I fooled with the two that I had here I would just leave the Degas bottle open not filled it too full obviously and then watch it all get sucked down when I call up the pump and then put the car in the run mode and just let it sit there and run for an hour if I want nothing's going to happen with this thing It doesn't even hardly get warm and just wait for that coolant to circulate around through every hose and every orifice and all of that and then see how much the stuff is dropped after all that's gone on top it up to the full mark and then go for a drive using the gas driving the car not it driving me and then from there I should have all the hoses heated coolant flowing heat at 45° out only need for about 5 minutes and then it's turned off because I'm in my outdoor clothes so and it's sunshine and all of that and I don't really have the windows down so it's getting right hot in the car just with the sunshine coming through the windows and me being dressed for the day.

 

It's tricky to get the how off, and you need to flush it from bottom to top.
And use white vinegar. Someone said that helps break down the fake sealer.

I'm not sure about the flap. Perhaps someone who's had one fail can comment.
Or do a duck-duck-go search for it.

You still haven't said if it's the radiator or heater hoses... or both

 

Should be getting hot unless the water pump is not pumping or the radiator is clogged.

The coolant reservoir tank and hoses are not an overflow system on these cars. It is part of the normal circulation but PARALLELS the radiator, allowing a small amount of the flow to bypass the radiator.

The fact it has already blown a head gasket and it was repaired diy points to several possibilities:

1. It has blown a hg again because the head or block is warped or head bolts were not all properly torqued. This CAN lead to combustion gas ("air") bubbles in the coolant. A drain and fill of the coolant can temporarily remove the "air", remove the gurgling sound and restore cabin heat. Temporary is the key word.

and or

2. The radiator itself is clogged. The flow through the bypassing reservoir loop continues but the main radiator flow path can still be stop leak clogged. This would require a new radiator as the micro channel radiator paths are not going to clear easily or with vinegar.

A pressurized coolant cylinder borescope test might be the best path forward. A combustion gas coolant test can be a true positive or a false negative for a hg leak.

If it's another hg leak, a rebuilt engine from a shop like Hybridpit ($3500) or a hopefully good JDM engine ($1500) would be my path forward.

Car Care Nut HG Borescope at 7:40

 

One stop-leak manufacturer recommended (to a member here, "might" have been @cnc97, that if you know their product has been used, to flush the system with a 50/50 mix of white vinegar and water.

Then I suppose a few more flushes with straight water, preferably distilled for the end of that process. After a last drain, you'll need to deal with residual water, which is impossible with pre-mis, like the spec'd Toyota Super Long Life coolant (only comes pre-mixed). In my signature there's one link on how to deal with that, just some thoughts. (on a phone turn it landscape to see signatures).

 

I'm never buying a used car again

 

I would never buy a used gen3 these days over 50k miles unless it was an imported and US certified 2018-21 Prius + or alpha. While that would be financially prohibitive, there might be a chance to get one of their late model JDM engines for a reasonable price.

 

Info from Repair Manual:

 

I would certainly rule out a damaged water pump or another hg fail before taking on the difficult radiator replacement.

When you do the radiator, don't accidentally disconnect the refrigeration lines on the ac condenser or damage the condenser.