MG1 and MG2 temps too high?

As a general rule of thumb, higher temperatures rapidly shorten the life of windings in motors:

Source: Why Motors Fail: Part 1 | Franklin AID

Heat is the enemy but there was a major change in the "Prius c" transmission cooling from the earlier models. The "Prius c" does not pass the inverter coolant through channels in the case to a coolant radiator. Instead it uses the transmission fluid, Type WS, as the primary internal heat transfer fluid and convection and radiant cooling.

Let me suggest searching for some of the earlier work on "transmission oil" or "transmission fluid" testing. You may want to do an early change and send the 'in service' sample along with a 'virgin sample' to an oil testing service. I use R&G Labs and their advice is a 15% loss in viscosity means the oil has reached the end of its life. This can also give a clue to what is going on.

My testing data, ~30 samples, suggests:

1. 5,000 mile early service change - removes the early left-over manufacturing debris and sealant leached material . . . all Prius.
2. Based upon the viscosity change - use an increasing interval of transmission oil change until a steady-state condition is reached. For the 2001-03 Prius, about every 30k miles. For the 2004-09, about 60-90k miles. I don't have a rate for our 2010-current, Prius hatchback, it just went over 38,000 miles so we don't have enough data to predict.

Based upon the change in the 'Prius c' transmission cooling design, I would recommend start a study and find out. My impression is the 'Prius c' might be a better urban than highway ride BUT I don't have one to test.

Other Prius we often use a 'radiator inlet block' to reduce cooling losses at temperatures under 70F. However, it may be the 'Prius c' could benefit from increased cooling airflow at highway speeds in warm weather.

GOOD LUCK!
Bob Wilson

 

You might want to experiment with hill-climb speeds. Many years ago I conducted a number of 'hill climb' tests at different speeds up an 8% grade. What I found is 55 mph was an optimum climb speed and matched the speed of heavily loaded, semi-trailer trucks often found in the truck lane.

So my practice is to use a moving van as a pacing vehicle on cross country trips. I keep plenty of space, no drafting, so I can steer around road debris. This approach gives pretty good, highway mileage and keeps the engine and transmission 'in the green.' As for time lost, well it depends upon how long the trip. If a typical DC area commute, it may only be minutes . . . not counting the non-linear, traffic effects.

I do recommend doing an early study of the transaxle oil wear characteristics. The 'Prius c' is new and the time to ask is when it is new, not later when other symptoms might show up. R&G Labs charges me ~$20 but be sure to ask for the 40C and 100C viscosity tests that give a clue to what is going on to the lubrication characteristics.

Bob Wilson

 

In general the MG temps on the 2010 start at ambient then take maybe 2-3 hours of driving to get up to the engine block temp. How do you like the Engine link? What type of unit does it feed from? Thanks. Ted

 

200 degrees F is nothing.............Your not even to the boiling point of water...Engine cooling temps exceed 200

 

The coolant thermostat engages at around 210 on the PC.

 

I am not sure of the differences between the 2010 Liftback and the c but the repair manual shows the high temperature alarms for the 2010 Liftback MG1 and 2 to be 320 and 334F. This is mighty high to me. On my daily commute I typically see these temperatures in the 160 to 180F range. Of course this is on relatively flat terrain.

Also the thermostat on the 2010 is 195F.

 

I'm basing my experience on my torque app and a bluetooth obd2 sensor.

 

Anything over 200F on the Liftback is considered above normal. 210F would be considered hot.

 

I think I've read that the inverter/transaxle cooling loop doesn't have a thermostat. Quoting engine thermostat values is irrelevant.

 

When did you make this observation?

I.e. had you been driving under high load (uphill), grille block, after 10min of driving vs. 2hrs of driving, ambient temps etc..

 

Sitting at a stoplight waiting on it to turn green. Got up to 210 and then suddenly started dropping down to about 180 as if the thermostat had opened. It acted the same way as all my other cars except that I couldn't hear the fan kick on like I could in the older cars.

 

Not sure about the app you're using, but we have a factory scan tool, and the temps you're seeing are perfectly normal. Rest assured that it'll let you know if something's amiss.

 

Since 2010, our Prius engines use an electric water pump. It is likely the latent engine heat triggered the control computer to start the pump which is why the temperature dropped.

Bob Wilson

 

The C's transmission shares no coolant with the engine or the inverter systems. It's "stand alone".

 

I wasn't saying it was an issue, just noting my observations.

 

But this is the transaxle/inverter loop. I vote it was the cooling fan kicking in.

 

Well I'll defer to those with the car. The SAE paper discussed how there are no inverter coolant channels to the transaxle and only air cooling is used. It makes sense one (or more) of the radiator fans is designed to force cooling air against the transaxle. The report of:

This "suddenly started dropping" suggested monitoring engine coolant which the electric engine coolant pump can engage without having to turn on a radiator fan. But this is a new Prius model and a previously unknown cooling fan for the transaxle could be exceptionally quiet.

BTW, I can initiate a similar drop in ICE coolant temperature in our 2003 Prius with the engine off by turning on the cabin heater. The heater loop has an electric pump that passes the coolant through the engine block. In seconds, the engine coolant temperature can show a 3-5C drop, consistent with the user's reported temperature change.

I remain curious about the Prius c transaxle temperatures as it uses a new approach to cooling. This is likely to show up in future Prius but I only have the SAE paper describing the changes. A better set of sources:

• New Car Features
• Maintenance Manuals

Not owning a Prius c, perhaps others have them?

Bob Wilson