Part of the issue I think here, is you're losing coolant somewhere and where the coolant is lost air is going to be present. So, as it cools down over night or just when it's off, it's going to draw air in through this mystery spot. And the coolant temperature sensor cannot read air temps, it has to be in coolant to read accurately. Even though the small spots you're seeing may seem unlikely to be the source of the leak, that's going to be the area to focus on, unless you see one of these heat exchanger units running down to the Catalytic Converter, the tech that mentioned this said he wasn't sure if this model had it or not, but it would look like a couple of heater hoses running down to the Converter. That might be the coolant boiling off down at the Converter, you just can't see it.
Something else I came across was this diagram of the Inverter Radiator. Which runs along the lower front end, an inverter is what changes voltages from AC voltage to DC voltage, and it produces heat due to the high voltage levels that the Electric part of the engine runs on. So, there are multiple areas where coolant is being transferred to that wouldn't be on a conventional engine. With your lower radiator hose being cold after hours of running, either the coolant isn't being circulated through the radiator or the radiator itself is clogged.
I went through service info on the exhaust system for this vehicle and didn't see any kind of heat exchanger. So that's something you'll have to take a look at while the vehicle is up on the ramps, I think you should try a pressure test yourself and see what you come up with. The Dealership techs get paid a flat rate time usually so if they can't come up with a cause in a certain amount of time, they are going to start throwing parts at it as they have been. I wouldn't be surprised to find out it's the radiator and the coolant is leaking out onto something and boiling off, and that's why you're not seeing any in the driveway or leaking down.
That would explain the noises you hear too. Do you think the reservoir is where some of the noises could be coming from?
I also see this "Bleed air from the hybrid motor cooling system using GDS". So, using their factory scan tool to bleed air out the system. I'm wondering also if there were any codes stored in any modules, it should be on any work orders or receipts they gave you, I'm sure you have a mountain of paperwork from all this, but for them to replace the entire engine, along with 4 head gaskets, why would they not go after the radiator or Inverter radiator as well.
I doubt they got it very hot running in the shop while diagnosing the issue, it's going to get much hotter while you're out driving for longer periods of time.
This is their service info on bleeding the system after the EEWP (electric water pump) 5th diagram. Its the same way I would bleed a normal vehicle, when cold, leave the radiator cap off and start the vehicle, and the coolant level will drop while air is escaping during warm up, then refill and put the cap on. I don't recommend you doing the water pump on this, the high voltage sections of the motor can be fatal.
But get the pressure test kit and see what you come up, the leak is only going to get worse and has to show itself at some point here.
Images (Click to make bigger)
Saturday, January 27th, 2024 AT 4:35 PM