You didn't say what year. For many years an optional tow package was offered, consisting of a larger radiator and alternator and an ATF cooler. Hitch and wiring were separate, and dealer-installed wiring was only 4-pin; you had to go aftermarket for full 7-pin wiring. The mechanical towing upgrades became standard in recent years, I believe, but you still have to add hitch and wiring. Check your owner's manual about the requirements for your year. A dealer can determine if it is equipped with a tow package if required- don't assume based on whether or not it has a hitch.
Fully equipped with trailer brakes
, all years are rated to tow up to 3500#. Practically speaking, I would not recommend towing right at the limit for a number of reasons.
First is the tendency to load up a minivan with people and/or cargo, which reduces your real-world towing capacity. Tow ratings typically assume the driver and one passenger, but no extra people or cargo.
Second and related, tongue weight
needs to be considered. A soft rear suspension and relatively low hitch can leave you dragging your tail if you get close to the 350# tongue weight
rating. Again, extra passengers and/or cargo in the van contribute to the rear axle
Last, frontal area and trailer shape have to be considered- there's a difference between a tent trailer, a low-profile rounded egg trailer, and a tall, wide, boxy conventional trailer. Tow ratings are usually tested with a low profile box cargo trailer (I see a lot of camouflaged new models being tow tested in Arizona). Anything wider or taller than the vehicle is going to add drag and tow like a heavier trailer at highway speeds.
I towed our 13' Scamp
(1700#) with a 2000 Sienna (194hp 3.0L V6). It towed the smaller trailer very nicely but did work hard on mountain grades with 4 people and maybe 150 pounds of cargo on board. With the more powerful 3.5L engine, full tow package, and trailer brakes
I'd feel comfortable towing something the size of a 16' Scamp
(2500#) but not much more.
We have since upgraded our tow vehicle to a Honda Pilot, but I considered another Sienna at the time. I loved the old Sienna and consider it one of the most practical and reliable vehicles I have owned. The new Siennas have gotten pretty big, one reason we opted for the Pilot instead. My kids still miss the minivan.
Tell us more about your Sienna and what you plan to tow (Exiss doesn't sound like any molded fiberglass trailer I've heard of), and I'm sure you'll get more specific recommendations.