Piston Slap: Crossing Over Into Minivan Tow Ratings?

by Sajeev Mehta

Updated: May 16th, 2014 Published: April 19th, 2012

piston slap crossing over into minivan tow ratings

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.

#Brakes #Crossover #Cuv #Gvwr #Minivan #Towing #TransmissionCooler #Weight

Sajeev Mehta

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7 of 23 comments

Toad on Apr 19, 2012

Crazy idea: RTFM and follow it. If the company that spent many millions of dollars engineering the vehicle components gives it a specific tow rating not to be exceeded, don't exceed it. Better yet, don't exceed 75% of it. Just because your engine has a maximum RPM of 6500 does not mean you would drive with the engine spinning that fast all day. Why treat your brakes and suspension with equal disdain? Engineers are actually pretty smart, and they have a pretty good idea about the overall limitations of the vehicle they designed. If you don't think they knew what they were doing when they designed your vehicle you should not have bought it in the first place. On the bright side people not towing properly provide lots of fun on YouTube.

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- Don1967 on Apr 19, 2012
  
  That doesn't explain why European vehicles consistently get higher tow ratings than North American vehicles of the same design. Unless one believes that Europe has less gravity, of course.
  
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- Sajeev Mehta on Apr 19, 2012
  
  @don1967 I'd be shocked if Euro and US (SAE) towing standards are using the same measuring stick. Not to mention that us 'Mericans in the flyover states tend to drive (well) over 70 MPH while towing on a regular basis...and most roads in Europe make that impossible to duplicate. That is a LOT of inertia to stop, and it doesn't exist in Europe. I blame the US Interstate system and our love of buffets. (kidding)
  
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- Bikegoesbaa on Apr 19, 2012
  
  Great idea! One thing - can I pick which manual I want to read? If so, I pick the European one that says my car is rated to tow 1,000+ pounds as-is; rather than the US one that says the very same car isn't able to tow anything. I'm confident that the engineers knew what they were doing when they designed the vehicle. I'm not confident that the marketing guys and legal eagles are setting different tow ratings for different markets based on sound technical reasons.
  
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- Luke42 on Apr 20, 2012
  
  @don1967 "That doesn’t explain why European vehicles consistently get higher tow ratings than North American vehicles of the same design." I did some reading about this, and I found that Europe has a towing-speed-limit that's under 60mph (maybe even closer to 50mph), no matter what the road type. So, if you're towing a trailer on a European equivalent of an Interstate, you're Expected to lumber along at 50-60mph, no matter how fast the other traffic is going. The European rules also favor different types of trailer braking systems, and they're required on more/smaller trailers. Then add in the marketing differences (it's easier to talk an American into an F-150 that they don't really need), and the litigiousness, and I think that's sufficient to explain the differences between the US and the EU/UK rules. "Unless one believes that Europe has less gravity, of course." [Pedantic didactic screed on the differences between mass and weight, as well as how weight creates traction, has been deleted for the sanity of all. Look in any physics FAQ for a discussion of weight vs. mass for the details.]
  
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- Luke42 on Apr 20, 2012
  
  @bikegoesbaa Ever notice that many World cars even have threaded holes for mounting a trailer hitch, even when towing is Not Recommended? But, as I said above, the differences go beyond just marketing and legal reasons. Trailer brakes and speed limits (for combination vehicles) are different between the US and Europe. So, if you promise to drive your car the way a European drives his car on a European road, then you can use the numbers in the European manual... Still, using artificially low tow-ratings for marketing purposes does hurt buyers here. For instance, I'd have bought a Kia Soul if the manual said I could tow 1200lbs with it. The UK version is rated to tow 2800lbs, and towing is contraindicated in the operations manual of the US version -- so, I bought a beater-Escape instead. In other words, I settled for a car that's less-well suited for my purposes so that I wouldn't have to prove to dealer service departments and/or cops who want to give me a rough time that my vehicle is capable of towing some very modest loads that the Soul's sheetmetal, suspension, and drivetrain really is capable of handling.
  
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Fatehunter on Apr 21, 2012

My car is a 2003 Audi a4 wagon with a 1.8 L turbo. The tow rating is 2000lbs and I tow 2000 lbs (pop-up trailer). Mind you, there are electric brakes on the trailer. Longest drive is from Prince Rupert in BC through the coast mountains down to Vancouver, BC. I also tow 1500 lbs of boat (+ trailer). No brakes on the boat trailer so I keep it below 110 km. I love the looks on faces when I use my audi to launch my boat (16 ft cabin fishing boat). My audi is my beater truck when it tows my full size utility trailer. a yard of dirt weighs near a ton so that trip is nice and easy from the dirt yard to home. You can tow if you stay with-in the capabilities of the equipment. Ask for more and you are not going to get it. However, here in NA we love to blame others for our own lack of fore-sight, in other places they say you can do it, but follow the rules. I have experience (lived in Holland for 7 years). With regards to the audi, The RV dealer was very surprised when the 150 lb tongue weight only dropped the back end of the audi by one inch. I think the suspension on this car make a big difference, as many minivans just drag with weight in the back. bottom line I think is that some vehicles are better suited just because of their basic construction standards. In reality my audi is a piece of shit, new(er) engine at 180,000 km because of a cracked head, all kinds of other shit including a steering rack adding up to $10000 (not including engine) over the last four years. I hate the ****ing car to maintain, but I sure love to drive it. Came from Subaru's, don't want to get another Audi, what do I do?

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