I have a recently-acquired 2010 Prius that has 255k miles on it. Six months ago during the summer it received a rebuilt engine after its former engine blew its head gasket. The new engine from another Prius was rebuilt by a trained Toyota tech, Scotty Partin. Scotty left the dealership/mothership that trained him and started his own Prius shop in SE Kentucky near Corbin. The rebuilt engine works great: zero consumption of oil or antifreeze after 5k miles of Midwest driving. It consistently gets 55+ mpg if I keep it below 70mph and purrs like a kitten. Hybrid battery's cells are all below 25 milliohms of internal resistance according to Dr. Prius. Has new Aisin water pump. All in all, a successful acquisition and re-engine of an aging Gen 3. The only negative is that the red over-temp thermometer on the eastern end of the instrument panel occasionally rears it head. The only instances are level ground driving speeds over 80mph when OAT is greater than 90 degrees F, or on long steep up slopes of western US mountains at 70mph when the OAT is greater than 65 F. If I slow down by 10-20mph the red thermometer will turn off and remain off. It never stays on long enough to log an OBDII error code. Other pieces of data: the air conditioning is ice cold at 90 degrees OAT, and I doubt that the AC could do that if the passenger side radiator fan is inoperative. And I never hear radiator fan noise when I bring the vehicle to a halt. I've been surprised at never hearing the radiator fans "overhang" the engine's run time, but assumed that Toyota did that intentionally as they did with the stealthy behavior of the blower that cools the hybrid battery pack. What is the likely cause of this rare engine overheating at high horsepower demands?
1. Does it lose coolant? 2. Any codes of any kind using a hybrid capable scanner? 3. What are the two coolant temperatures reading normally and when the light comes on? Both radiator fans should run anytime the ac is on with the car not moving. However at speed they are not needed so they are unlikely the cause at high speed. A properly functioning cooling system should never hit 220f and will normally run 200f or less even at highway speeds in 100f ambients. Knowing the temperatures goes a long way to diagnosis. The warning light comes on at 248f so there is an issue. There have been cases where the temp sensor on the engine is ok while the temp sensor on the return hose of the exhaust heat recirc system is pegged high. Techstream's sensors are both called Coolant Temperature. The Car Scanner app with bluetooth uses Coolant 7C0 and Coolant 7C4 designators. The second and third lines of descriptions on the pic were manually added for clarity.
rjparker, thanks for the quick response to my posting. No, there is no coolant consumption in more than 5k miles. I'm out in California right now with my wife and this car. I have my Bluetooth OBDII adapter and an Android tablet, so I can fire up Torque Pro and Dr. Prius this week and use these apps to read temperatures and OBDII codes. Dr. Prius does a good job of detecting all hybrid-specific OBDII codes. It has smelled some that my Innova tool cannot see. Happy New Year from 65 degree F Blythe, CA on I-10.
rjparker, is the "Car Scanner" app you mention the one found in app stores called "Car Scanner ELM OBD2" offered by Stanislav Svistunov?
Do you know if the previous owner put any of the so called stop leak in the coolant? If they did, your radiator is likely clogged, along with the heater core, egr cooler, and other small hoses. You could have air in the coolant system also. Are you CERTAIN the radiator/condenser fans are functioning correctly? Have you monitored the coolant temperature? What about the inverter temperature? Perhaps it's the inverter that is overheating? Driving the Prius like a Prius instead of an F1 car should keep the light off, but it's not resolving the overheating issue, but it will help to keep you from buying another engine until you find the issue...
