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Mike writes: Dear Sajeev, I have been a fan of TTAC for a while now. I am motivated to write by the recent responses to towing with a 2005 Odyssey. Two years ago I bought a 2008 Toyota Sienna and a 21 foot (actual total length) travel trailer. The trailer has a GVWR of 3500 lb, which the Sienna is rated to tow with its towing package. I had an independent shop install a fluid-to-air ATF cooler, unfortunately, perhaps, choosing the smallest model as it was recommended for a 3500 lb tow. I was concerned about getting too much cooling in the winter. The van already had an ATF cooler in the radiator. I had them put in an ATF temperature gauge (before the radiator) at the same time. The towed weight of the trailer is several hundred pounds below the GVWR, but it has a front profile that is basically vertical. I have towed the trailer about 20,000 km (yes, I'm in Canada) and done what Toyota calls an ATF change three times. That's actually a drain the pan and refill with 4 L of ATF, not really a change. Of course, I have no way of knowing how accurate the gauge is, but the highest it's been on the highway is 220 F on a couple of grades in the BC mountains (Coquihalla highway). The temperature went down as soon as the grade did. It went up to 240 F or so for a few minutes while backing up a steep hill and around a bit of a corner into a storage yard. The van had 38,000 km on it when purchased and is now at 82,000 km. Enough background. I am writing to ask why it is apparently okay to tow a larger trailer (5000 lb rating) with a Highlander but not a 3500 lb trailer with a Sienna. As far as I can tell, the engine, transmission and weight of the vehicles are basically the same. The internet is rife with posters who advise against towing with a minivan but seem to have no qualms about doing so with a SUV, except the very smallest. What do you think? Thanks very much for helping me out with this. I can find no answer to my question on the internet.
Sajeev answers: Wow, you actually put an ATF temperature gauge (among other things) in a minivan? This is why I love TTAC: our readers do some rather brilliant and enlightened things outside of their computer time. Well, at least some of you. I kid, I kid! There are crucial elements that go into a tow rating: the vehicle's weight, braking capacity and rear spring stiffness. The 2012 Sienna is about 200lbs heavier than the 2012 Highlander, for starters. Who knows, maybe the brakes aren't good enough for a Highlander sized trailer and the Sienna body. Ditto the rear springs. I never had much faith in manufacturer tow ratings, until the Society of Automotive Engineers (SAE) came up with their Surface Vehicle Recommended Practice J2807: which supposedly standardizes these figures. Is J2807 is be all, end all of towing standards? Maybe so, but this terribly formatted article gives you more insight. Definitely cut and paste this one into Word before reading. While this many not fully answer your question, hopefully this will tow you (sorry) in the right direction. Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you're in a hurry.
from The Truth About Cars http://www.thetruthaboutcars.com | 
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