Transaxle temperature limit

I understand the ATF to be the most temperature-limited thing in there, and that should be good up to about 125°C

 

In the Repair Manual series (more info), the malfunction thresholds for the “Drive Motor ‘A’ Temperature Sensor” (P0A2B, P0A2C, P0A2D, and P0A2E) and “Generator Temperature Sensor” (P0A37, P0A38, P0A39, and P0A3A) diagnostic trouble codes are either not mentioned at all or stated only as “TMC’s intellectual property,” that is, trade secrets of Toyota Motor Corporation.

The Data List pages give the following “Normal Conditions”:

Motor Temp No2 (MG1 temperature):

While driving at an ambient temperature of 25 °C (77 °F):
25 to 100 °C (77 to 212 °F)​

Motor Temp No1 (MG2 temperature):

While driving at an ambient temperature of 25 °C (77 °F):
25 to 90 °C (77 to 194 °F)​

I don’t know if temperatures above these limits are necessarily abnormal, however.

 

That's roughly the point where some permanent chemical changes will start to occur in many oils. The oil breaks down a little bit, can form some waste deposits aka sludge and lose some useful lubrication properties.

A few hours per year at 116 isn't going to hurt anything.

My own theory is that with the lighter weight of the Aqua model, they were able to simultaneously eliminate leak potential, reduce the amount of coolant required and trim the parts count a little. All good for cost savings and even further weight savings. Similar to the use of a single radiator fan where all the big Priuseses have two.

 

I've gotten MG1 and MG2 to higher temperatures and at some point the car goes into a 80% power mode to protect the system.

 

I remember a while ago that someone mentioned 325F is when the light comes on.

 

I don't remember but maybe some searching might show. I want to say that it was a temp warning with the red triangle.

 

My experience with a v is mg temps are close to engine temps. 240f would be way too high in my case even though the stated limit is at 323f. In the v design there is an extra coolant loop from the inverter pump to the transaxle because of the v's higher load carrying capability. As a result transaxle temp can impact inverter temps which are alarmed at 149f. That loop goes to the inverter first, the transaxle and back to the radiator.

 

Actually the v’s transaxle coolant source could be the engine water pump. (Edit: It is the inverter water pump. See below)

Recent 102f Ambient after Freeway Drive

 

Nope, the engine has one cooling system, and the inverter and transaxle have the other one.

v is a little bit different in having a second water jacket on the MG2 side. (Those passages are also present on the non-v Gen 3 liftback transaxles—it's the same aluminum case—but without the cover plate and hose nipples to close them off and make a usable water jacket.)