Originally Posted by cyclopath
I have a 2008 Lexus 400h (hybrid) and have pulled my Escape 17B over 15,000 miles without any problem whatsoever. The car has a “Towing Package” (whatever that is) from the dealer.
Typically in Toyota non-truck models (such as my Sienna) the towing preparation package
is whatever is needed to allow the vehicle to operate reliably under the heavy sustained load of towing. In many (but not all) years this includes a larger (or even additional) transmission fluid cooler. In a Sienna with the 2GR-FE (3.5L V6) engine - but not with other engines - it includes an engine oil cooler. In some it includes a power steering fluid cooler, often it includes a higher-output alternator, and occasionally it involves rear suspension modifications. In a Toyota/Lexus, this is not a dealer-installed package; it is optional factory equipment.
To tow the vehicle needs a hitch and wiring
for lights. These may be bundled together and sold as a "towing package". While they are factory-installed in many vehicles, in non-truck Toyotas they are accessories, available from the dealer (and then usually installed by the dealer) or aftermarket. Some Toyota dealers sell aftermarket equipment and either install it themselves or send the vehicle out to a hitch shop for installation.
A 2008 RX350 has the 2GR-FE (3.5L) engine, but a 2008 RX400H has the 3MZ-FE (3.3L V6, the same as my Sienna). While the RX350 probably gets an engine oil cooler in the towing preparation package (the Sienna with that engine does), the RX400H would not likely get one (the Sienna with that engine does not).
The RX350 has a conventional automatic transaxle (and usually 4WD), while the RX400H has a Synergy Hybrid Drive transaxle, so changes for towing are likely completely different. It is unlikely that the hybrid gets a transmission oil cooler (it doesn't have a torque converter or clutches so it shouldn't need a cooler); on the other hand, the electric motors and controller of the hybrid system get a cooling system (with water/glycol coolant like the engine) so there could be a change in that for towing... although I've never heard of drivetrain changes for a Toyota hybrid for towing.
I suspect that there is no towing package for the hybrid RX (or Highlander), and that the "package" in this case is just the hitch receiver and wiring.