engine overheating, dealership is stumped

Hopefully they check the radiator electric cooling fan operation as well as making sure the AC condenser airflow is not obstructed with insects and leaves.
Does your scangauge allow you to monitor the radiator fans?

 

I think a trip to a different dealer is in order......

 

Although not common on the Prius engine after checking the drive belt to the coolant pump, the pump itself, and the outside of the radiator for blockage, and of course the thermostat. The next thing would be a suspect head gasket.

John (Britprius)

 

Im betting on the fans, the fans are used the most when the engine is hot and there is insufficient airflow. I.E extended idling or low speed driving.
I suspect the radiator is sufficiently cooled durring your highway speeds but needs the fans once you stop or are operating at low speeds which is no longer moves enough air through the radiator.

 

Where is your location and what's the temperature currently like there?

Also, have they checked the oil and the coolant to make sure there's no sign of a blown head gasket?

Wow John, you posted that while I was typing.

 

You've got to be quick these days.

John (Britprius)

 

From the OP's description of the event it didn't sound too much like low speed driving to me. Just one rest stop on the freeway and the Prius shouldn't have been idling at all. It's hard to know how demanding the operation was on the cooling system without knowing the ambient temperature or the terrain the OP was operating in.

 

It is not unknown for the fans to be in the wrong positions if front end damage work has been carried out. This can be checked by turning on the AC and standing in front of the car. If air is blowing out of the front grill the fans have been swapped.

John (Britprius)

 

Too bad their senior tech doesn't understand that the coolant heat recovery storage tank wiring will have nothing to do with an engine overheating issue.

I would agree with the posts that the most likely cause would either be reversed cooling fans (the fans should be sucking air from the radiator) or substantial air in the coolant loop. You can check both of these items:

1. Turn on the air conditioning, MAX COLD temp setting. Both radiator fans should be running. Observe which way air is flowing, to verify the fans are spinning in the correct direction.

2. Turn on the heat, MAX HEAT temp setting, maximum cabin ventilation fan speed. Do you have good heat coming out? Do you hear any gurgling air bubbles? If your answers are yes and no then hopefully you don't have air in the coolant loop.

 

I can attest to that. My x-wife had a front end collision with my 07. After the repair, I had the same symptoms. The fans were reversed...

 

Odometer reading?

Are you aware of any issues besides the engine overheating episode which would have stressed the engine and damaged the cylinder head gasket?

I suggest that you request a cylinder leakdown test be performed to verify a problem exists with the cylinder head gasket.

The radiator is typically operating at ~15 psi. An engine cylinder will experience much higher operating pressure. Typically the pressure is over 100 psi just at 300 RPM cranking speed (for a normal gas engine) so it will be much higher when the engine is revving up.

 

Assuming they are sniffing 142 ppm of HC at the radiator neck, there is an internal engine concern, most likely a head gasket or cracked/warped head.

 

I am glad the the problem has now hopefully been resolved, but feel the dealer let you down by not carrying out a simple test checking for exhaust gasses in the rad.

Hopefully it is just the head gasket and not a cracked head "not trying to scare you but it is a possibility" however unlikely.

John (Britprius)

 

I have a 2011 prius (I guess gen III) at like 135k I started getting a "rattling noise" from the engine.. I got all oil changes etc done on time, I did a perfect maintenance. They checked everything, and finally found out that head gaskets are damaged.. No check light, no overheat warnings. And the engine kept on losing coolant slightly (it was going into the engine) - the dealer couldn't explain why this happened.. I ended up spending $3500 to get head gaskets, coolant circulation pump and the heat sensor replaced.. the service never took a small responsibility on behalf of toyota.. They tried to sell me a new prius...

 

welcome!
uncommon, but it happens. sorry you didn't connect with us sooner, a salvage engine is typically a better route.
all the best!

 

Another engine destroyed by dealer maintenance.