2002 Prius high coolant temperature warning light on and can't rev/drive

Sounds to me like the thermostat in the engine is stuck closed. when that gets stuck closed it wont let the coolant flow from between the radiator and the engine. i would start by replacing that. they are not expensive.

 

how many miles on this car, what did you pay for it?

 

Is the drive belt (belt from crank to water pump, and AC compressor) still on the pulleys? If it broke no engine water pump = hot engine. Any signs of coolant leakage around the water pump? Get someone to scan the error codes with a Hybrid friendly scanner...maybe there are other codes present you cannot see with basic scanner.

When heater is on does that help keep the engine cool?
Any "milkyness" in the engine oil or white smoke coming out of tailpipe?

 

good thinking paul. didnt think of the little belt.

 

Yes.

 

When I bought my 2003 Prius, I ordered $300 of maintenance manuals from the Toyota Technical Information System. They also have an online service with daily and monthly rates.

The next purchase was a Prius aware scanner, used, which in 2006 was the Graham Miniscanner. Standard OBDII scanners know only the emissions interfaces, not the half-dozen control computers that operate our cars.

You might consider investing in the manuals (they are available on Ebay, any 2001-03 would work for your purposes) and a Prius aware scanner. You're one leg up in knowing about OBDII but our Prius use ISO-9141/KWP2000. Emissions data is just a fraction of the information available (and often needed) to efficiently maintain and operate our cars.

GOOD LUCK!
Bob Wilson

 

I would see about investing in a scangauge 2 which can be had at autozone for 160. it has this xgauge feature to access the hybrid system, if you can text you can do the xgauge feature. i have one and it works well. if you get one you have to contact linear logic the company that makes it and tell them you bought a scangauge for a 2001-2003 prius and they will send you a modified cable for free to work with our cars.(the one that comes with scagauge sets off the abs/brake light. its false code because of the cable). you could also get Autoenginuity , that could run you about 500 and you will need a laptop but its going to tell you everything.

 

with you having one hose in the radiator cold and the other hot, I would start by replacing the thermostat in the engine.

 

when you have the car sitting with key on or anything look at your inverter(silver square that says Toyota Hybrid System) at that tiny tank on the top left, the level in the tank should be equal. now turn the car to on, dont start the engine. now go look at the inverter again, you should hear something running. look at that tank again the coolant in the front of that tank should be higher than the back. take the cap off, you should see the coolant moving around in there. if not, that that inverter coolant pump failed. which is common if its the old style pump(black base. New style has silver base). But to me as i stated above sounds like a stuck engine thermostat.

 

Welcome to computerized cars. yes. when that comes on the car goes into limp protection mode so you dont cook the engine. also since mg1 the generator in these transmissions is between the engine block and transmission it helps so you dont cook that either, i am assuming. but most definitely its a protection built into the car. dont mess with that or disconnect it. you dont want to fry the engine. if im wrong correct me on this guys

 

Without metrics from a Prius aware scanner, I don't feel comfortable speculating about what is going on. However, the car heater can be used as 'secondary' radiator.

The Prius cabin heater has a 12V coolant pump to circulate when the engine is off. In theory, you could set the heater control to maximum and maximum fan to mitigate hot coolant. HOWEVER, you really need to read out the engine coolant temperature. Even a 'brain dead' emissions-only scanner should be able to read out the engine coolant temperature.

Note that there are some resistive elements in the cabin heater that are supposed to provide 'instant heat' in cold weather. I have not done any experiments in this area so you might want just get the cabin temperature control to max and back a bit. This is just speculation, not based upon hard testing.

GOOD LUCK!
Bob Wilson

 

When you drive it, do you hear a speed related "hummm"?

If you shift into "N" does the "hummm" remain?

You are describing the classic symptoms of a failed, MG2 stator. If you get a sample of the transaxle oil, you'll find it looks and smells 'burnt.'

Assuming it is a failed transaxle, a salvage replacement should cost $1,000 or less. There are more advanced rebuilding techniques but it is doubtful you'll find an independent shop willing to do the job.

Bob Wilson

 

skboopalms,
Start by reading this.
Luscious Garage | Blog | Gen 1 Prius Transmission Failure, P3009, P3120

Then read this.
Luscious Garage | Blog | Gen 1 Prius Transmission Repair, P3009, P3120, P3125

At a minimum, this should help you understand the problem and what you're possibly faced with. As Bob says, you have described the classic symptoms of a failed MG2 stator.

Bob, Paul,
What would be the possibility of having the stator rewound by a motor rewind shop? To me (in my pea brain), this seems like the cheapest alternative???????

Here's how I envision it
Remove the MG2 stator, bring it to the motor rewind shop, have them rewind, replace stator and be happy.

What are the issues involved with why this cant work b/c $1300 for a new stator hurts.

 

I don't know if a rewinding shop would work and would be interested in hearing the results. This is what little I know:

• The NHW10, first Prius, had internal seals to keep the transmission oil separated from the rotors and stators. These internal seals were dropped with the NHW11.
• The Toyota SAE papers discuss potting compounds and processes as advances between the NHW11 and NHW20.
• Department of Energy papers noted the winding separators in their tear-down analysis but I didn't see any insights to the role they play.
• The Toyota SAE papers for the ZVW30 and prius c indicated changes are still being made in the stator winding technology BUT it isn't clear beyond manufacturing efficiencies that these have any 'life time' effects.
• Be sure the winding shop knows it will be in an oil bathed area as they choose a wire with better tolerance to the ATF.
• One interesting paper about winding shorts in the Japanese bullet trains traced to small air bubbles in the potting compound that allowed formation of coronal discharges that ate the potting compound. The paper also addressed detecting microwave signals in the power leads to the motors as a way to detect these coronal discharges. It remains an area of latent interest to me.

Bob Wilson