Modify a Prius for Towing?

I'm interested in towing a 1500 pound Teardrop style trailer on vacations.

The range of opinion on towing with a Prius goes from "No way" to "I've pulled a 1700 pound trailer over 15,000 miles with no problems". So let me acknowledge as a start that the official position of Toyota is that the Prius is not designed for towing. They would rather I purchase one of their larger vehicles. So much for CUA and "you really need the more expensive ...". It's my car, I think it's legal, so what would it take to make it work?

Obviously the first item is a hitch. There are a variety of hitches, most with 1 1/4" connectors. For towing purposes, is there any reason to choose a 1 1/4" unit versus a 2" unit? The lowest rating of hitches is class 1, which covers up to 2000 pound trailers.

Among the accessories that hitch websites mention are transmission radiators. If a big vehicle designed for towing needs extra transmission cooling, then a smaller vehicle pushing its limits certainly needs something like this. My first cut idea is to install a small radiator in front of the existing radiators, connect plumbing from the drainplug to an electric pump, on to the radiator. Return line goes to the fill plug on the transmission. There may be some way to connect the plumbing to the transmission oil pump cover, but that needs some more research.

A Scangauge can be used to monitor engine water temperature, and I think MG1/MG2 temperatures are available on the CAN. Transmission oil temperature is not available, and I think that is an important value to watch.

The Prius engine/electric power is adequate to tow a small trailer everywhere except up extended hills. When the traction battery is run too low, the gas engine can only drive the car about 45 mph up an extended hill. I could just live with that limitation and join the trucks in the right lane on extended climbs. Or maybe I could add more battery. The cheapest extra battery would seem to be an ordinary used Prius unit from a junkyard. This wouldn't be for use as an EV, but for extra capacity on extended uphill towing.

The brakes don't seem to be a problem. The trailer I have in mind has its own brakes that automatically apply when some sensor determines that the car is braking. So the trailer would seem to require some small additional braking on the part of the car, but not much.

So what do you all think about this? What have I missed? What's going to break first?

 

I agree that watching the temperatures is the first order of business. I know the MG1/MG2 temperatures are available to a Techstream, but I haven't found any Xgauges for them. The one I'd really like to have is transmission oil temperature, and that doesn't seem to be collected. That and a positive indication that the inverter coolant pump is functioning.

But all measuring can do is to tell me when I've pushed it too far. That's sort of my starting assumption, and the real project is to add more cooling.