2007 Prius Coolant Issue - Help

Hi guys.

My youngest son recently purchased a 2007 Prius with 194k miles on it. When I was driving it home from the dealer, the check engine light came on. I drove it home (~45 miles) with no issues and no other indications of an issue other than the check engine light.

Later that evening, (a few hours after we had gotten home) I was pairing his phone with the car and the Master Fault Indicator (big red triangle) came on and it indicated an over temp. I had the engine on while pairing it. I shut it down and left it sit over night.

The next day I filled the radiator and took it to AutoZone to have the check engine code read. It called out the coolant flow control valve. I had him buy a new one and we replaced it. Check engine light went off. Again I topped off the coolant.

He proceeded to drive it for a few days and the master fault started coming on accompanied with an over temp indication and they would go back off a few seconds later. I had him park it in the garage and noticed condensation in the driver's side headlight. Once the engine cooled down I checked the fluids and topped off the radiator again.

After reading several posts here and other places on the internet, I thought perhaps the inverter coolant pump had a leak since it was right under the headlight with the condensation. We replaced the pump and the condensation issue stopped.

Now, however, it is blowing coolant out of the overflow tank. The entire underside of the car gets soaked and dripping when I take it out for a test drive trying to diagnose the issue. We replaced the thermostat thinking perhaps it was sticking. No change.

All of the hoses are good with no signs of pinholes or cracks. The radiator is dry and doesn't show any obvious signs of a leak. There is no water in the oil. There is no oil in the coolant. The exhaust is not blowing steam. I borrowed a block tester to check for exhaust gasses in the coolant system and it came up good.

I understand that the overtemp/Fault Indicator going on and off can be indicative of an air bubble in the coolant system. I have bled the air out via the bleeder valve on the driver's side of the radiator. I have made sure the overflow tank is not over full and still has coolant in it when the engine is cold.

I am totally at a loss as to why this car blows so much coolant out of the overflow tank. I cannot get it to happen when sitting idle in my garage. It only seems to happen when under load (ie driving it). I have even jacked up the entire front end of the gar and put it in gear to get the transmission going and ran it at speed (55 on the speedometer) for about 15 minutes in an attempt to simulate a drive.

Any and all suggestions will be appreciated. I'm at a total loss.

 

Forgot to summarize what was done so far.

Replaced coolant flow control valve
Bled the radiator
Replaced inverter pump
Bled the radiator
Replaced radiator cap (twice)
Checked for presence of exhaust gasses
Replaced thermostat
Bled the radiator


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The coolant appears to be coming out of the overflow tank. The mouth of the breather hose is wet and the coolant level in the overflow tank is higher than it was when I started.

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Also, everything below the breather hose is soaked. From the mid point of the fans down it is dripping.

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No coolant visible under the hood when the vehicle was bought. Water pump belt is present and tensioned.

The check engine light wasn't checked immediately because I don't have a code reader and the auto parts stores were closed when I got home. So it waited until the following morning.

When the code was checked it was a P1121 which calls out the coolant control valve. We bought a new one and it was replaced. The check engine light cleared and has not returned.

I have no doubt the issue existed when we bought the car.

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Thank you all for your input. I just got back from having it looked at. It appears that we do have a blown head gasket. So now I'm going to start calling around for quotes. Anyone have any suggestions or preferences for a good service center in the NW Atlanta area? I'm going to start calling dealerships, but I can only imagine what labor costs are going to be.