2013 Prius Flat Towing

There will be plenty of people on here who will discourage you, but my suggestion is to not only go for it, but figure out how you can control the Prius shifting mechanism from inside the tow vehicle... It's a pretty big challenge, but being able to shift from neutral to drive to B mode from inside the tow vehicle would be impressive. And even more than that adding a trailer emergency brake system would push it over the top.

The former could possibly be done by buying a pushbutton replacement shifter for Gen3 Prius and wire that into the towing wiring harness with a bypass switch to make sure the Prius doesn't get confused about which gear shift to listen to.

The latter would be much more difficult and would require blending a standard trailer emergency brake system into the Prius' existing brakes.

Let me know how I can help?

 

The manual says don't. I don't know all their reasons. If the car were to be towed in "N" in "READY" state, two obvious problems would be that the traction battery would soon run down, and that 65 mph would overspeed MG1 (motor-generator #1). Towing in "D" would have other implications.

 

Incorrect... If the car is in neutral the battery circuit will be disconnected entirely. What's more the shifting mechanism gets ignored w/error beep if car is in ready mode and transmission is shifted into a position that could damage the car. For example, next time you're driving on the freeway try shifting in reverse. It will beep to tell you that it's ignoring your Prius destroying behavior!

 

Oh, really? Where do you think power comes from to maintain "READY" state when the car is in "N"? That includes the pumps, computers, sensors, instruments, etc., which total roughly two or three hundred watts of power. Plus whatever electrical loads the driver has turned on. Have you not heard of the sad tales of people discharging the traction battery by spending too long going through a car wash in "N" with the air conditioning on?

 

You're welcome to shift into neutral at anytime while driving at any speed to prove yourself wrong! 220V DC Hybrid battery pack provides 12v DC power to run all the vehicles systems in ready mode... No 12v battery required unless computers notice you disconnected them from 12v charging.

 

You don't want to do it.

The transmission in these cars is really, really different from everything else on the street. There are plenty of cars where you can just idle them in neutral and expect the idling engine to spin the ATF pump inside the transmission and everything is groovy. But not in the Prius.

Because the Prius doesn't idle, they couldn't do an engine driven ATF pump. But guess what? The Prius transaxle doesn't need one- there's no valve body hydraulics, there's no clutches or bands to tension.

The catch is that flat-towing a Prius presents a completely different mechanical problem vs. a regular transmission.

The Prius CVT regulates engine speed and crucially, the speed of motor-generator #1 (MG1). Normally the computer exercises tight control of MG1's speed as a regulating force for the gas engine.

The Prius cannot control MG1's speed while in neutral- cutting the power is specifically how neutral is achieved.

With no control authority over MG1, any torque input on the wheels is going to be distributed unevenly back through the power split device (the hybrid transaxle) resulting in... unpredictable RPMs for both the gas engine and MG1.

Once over ~38mph or so, the base gear ratio in the power split device allows enough multiplication to over-rev MG1 (>10kRPM) if the gas engine somehow chooses not to be deadhead-dragged up to a higher RPM itself. And you're burning extra gas in the RV to do that extra useless work.

To say it another way: there is no mechanical neutral that disconnects the wheels from the powerplant in a Prius. It can only be faked electrically, and such use is really only practical for low speed purposes.

 

Why risk wrecking the drivetrain when you could just use a dolly?

 

Dollies cost money to buy, register & maintain. They take up space. They can be noisier and clankier than other tow methods. It takes longer to dock and undock, and more of that work is down in the mud.

There's lots of reasons to prefer a flat tow, but you need just the right vehicle to enable it. The list of compatible vehicles is getting very short and the Prius was never on it.

A dolly or transporter trailer is 100% appropriate for a Prius.

 

I'm not going to try it If I need to go anywhere usually I need to go in the Prius not drag the Prius behind some big piece of something so I'll have it when I get there if I need to do something like that I'll drive the Prius and put my motorcycle in the little t niny trailer made out of plastic that the bike goes in then when I get there I have a 70 mi per gallon vehicle versus a 45 to drive. I do that pretty regularly. If for some godforsaken reason I have to rent a high hat sprinter van to go to DC to pick up furniture or do whatever unfortunately the Prius stays home because I'm not going to need to drive it around when I get there when I get there I'm loading up sitting talking having dinner with my brother leaving out the next morning back to here or such. But good luck with that be interesting to see how it goes.

 

Yeah registration raises some questions. Some states require it, some don't. Some require it for commercial use vs noncommercial use.

Best to check with the DMV before buying one, but AFAIK the OP's location (Oklahoma) doesn't require noncommercial trailers to be registered (I could be wrong, and frequently am )

 

Thats very smart

 

There is one, though; it lives in the cover plate (far end of the tranny from the engine) and is driven by a skinny shaft that runs through the hollow ring gear shaft to mate with the planet carrier/intake shaft. And it always has seemed weird to me, because of course it does nothing when the engine is stopped.

It's not the only way the tranny gets lubed. There's also simple splashing that happens, and there are some catch basins formed near the top of the case that catch oil splashed up by the gears, and it runs down through some passages to drip into bearings and over the MG windings.

So there's a combination of that and pumped lubrication going on, with the pumped part only happening when the engine turns. Just which parts depend on the pumped part, that's not something I know.

Two reasons besides lubrication, one already mentioned, to avoid flat towing are:

1. MG1's rotor has a maximum safe rpm of the mechanical kind (the kind beyond which centrifugal forces can shred it). The limit rpm (and corresponding road speed) were lowest in Gen 1, and have been raised in later generations, but still do exist. When the car is awake and in control, MG1 is never allowed above that rpm; the engine will be made to turn then, which brings the MG1 rpm down. If the car is not READY, it can't do that.
2. MG1 and MG2 are built with permanent magnets, meaning there is no way to stop them generating voltage when they spin. In neutral, they are both left open-circuited, where the voltage they generate goes right up alongside rpm. That may sound harmless because they're open-circuited then anyway, but only up to a point: everything involved (their insulation, even the transistors being used to open-circuit them) have upper voltage limits.

Toyota has (kind of briefly and sketchily) mentioned both of those things in their recommendation not to flat-tow the car.

 

I did not see this comment earlier- there may have been a miscommunication?

Dollies are a perfectly safe way to move a Prius. Safe to do engine off, no need to run the car at all.

Sorry if this wasn't clear earlier.

 

A tow dolly is fine if the front wheels are on the dolly but a problem if rear wheels are on the dolly so Toyota probably just decided to not create confusion by saying no tow dolly... Same reasoning as they say that a Prius is not for towing anything. Truth is it can tow lighter loads but easier for Toyota not to set a number of max weight for towing and just say no towing.

And if you really want to take care of your Prius and have the safest possible towing set up then buy an enclosed trailer w/emergency break system that Prius just barely fits into and then climb out the back hatch once you get it inside. That way the Prius stays clean and dry when you drive.

 

That's weird. Like Leadfoot says in the the previous post, your comment wasn't visible yesterday. Maybe a moderator can explain what went wrong?

Back to your question - I don't know why Toyota recommend in the owner's manual that you don't use a dolly. Mine didn't come with a manual so I can't verify.

Liability reasons maybe?

 

So, is the traction battery disconnected entirely from all the vehicles systems as represented in your first post, or still connected as represented in your second?

And if the traction battery is powering the 12V volt, but nothing is recharging the traction battery because the car is in Neutral, what keeps it from draining flat during an all-day tow?