Towing with a HiHy in the Mountains

Not sure what the HiHy comes with for oem tires, but one would have to speculate that like the Prius it would benefit from a tire upgrade. As you say the issue seems to be traction, not power. In the Prius at least the traction control keeps you from spinning the tires as you could quickly burn out the electric motor with no loading on it.

Good Luck!
Rob

 

In the ideal case, you would have the capability to monitor temperatures of MG1 and the HV battery. My experience with a well-instrumented 2001 Prius, very heavily loaded in mtn driving was that those 2 temperatures can get higher than I'd want them to.

If the Highlander HV battery has a similar cooling system design to Prius, the best way to lower battery T is with the air cond blowing cold and flow-through (not recirc) mode. There is no way to cool off a hot MG1 other than to stop the vehicle in 'ready' and let the inverter coolant pump do its thing.

The CANVIEW for 2004-onwards Prius can show HV battery temps at least, but I don't know about MG1, or if it is compatible with the Highlander. Possibly other equipment (such as scangauge) can show the important temperatures?

All of this may represent an abundance of caution. If you are doing high-load driving and get any sort of caution message on the dash, just don't ignore it.

 

I have towed 1750lbs with the Prius from Vegas to LA and back, so some 4200 foot passes. My only concern was overheating the MIGs, so I took care to accelerate extra slowly to minimize stress o the electrical motors. After that the ICE took the load.

The ICE was OK except on two of the long inclines when it was running near full RPM's to make enough tourque to get up the hill. 45 MPH seemed to be the fastests the ICE could keep the car going given the load and no electric torque boost.

 

I would seriously doubt it, based on how the Prius behaves. If the hybrid system was overheated there would have been all kinds of lights flashing on the dash. This sounds exactly like what a few users have reported when they are traction limited. Starting on a loose uphill surface, particularly with a heavy load, is pretty much the worst possible scenario for traction. Since the car has complete control over the power delivered by both the electric motors and ICE it modulates this instead of pulsing the brakes like some vehicles do. If the system detects wheel spin, it drastically reduces power output. The reported symptoms of TC taking over is as if the car has shut down. No pulsing, no spinning of tires, no reving ICE. Just the quiet of the electric motor delivering just enough power to keep the wheels from slipping but not enough to move forward. This seems to occur in situations where the vehicle would not have had sufficient traction to start so the fact that TC isn't letting you try is somewhat irrelevant. Backing down to a flat and getting a little speed up often seems to do the trick, as in most traction limited conditions. There is no way to disable the TC as this would risk damage to the electric motors. The sensitivity of the TC system was supposedly adjusted in the 2006 timeframe, and is much improved. There are also a lot of reports that this is simply not an issue with decent tires. The stock tires were selected for their low rolling resistance, but leave something to be desired in the traction department.

Again this is all with regards to the Prius, based on the assumption that the Highlander is operating in a very similar fashion. I personally would not hesitate to take a HiHy into these types of conditions. Particularly with good tires. From what I can see the HiHy's seem to come with either Goodyear Infinitys or Michelin Energys. Both of these are basically car tires. I went with Yokohama Geolander A/Ts on my Land Rover and they've been great. Not sure how they would affect fuel economy though. Of course you'd probably still get much better mileage in a HiHy with A/T tires than in any other vehicle you might use to tow that load. A/Ts might be overkill for your requirements though anyway.

Rob

 

Thats pretty impressive considering the Prius' towing capacity is 0 and payload capacity is only 863 lbs!

Rob

 

Yes it is. shhhhhh don't tell Toyota. Doesn't really matter now I have 141,000 miles on the car.

THe 1750lbs doesn't include the 3 people and luggage inside the car. Another 600 lbs.

Averaged about 29 MPG for the trips.