Towing in D

I’m sure this is a dumb question but here goes. I have a 2009 Tacoma double cab 4x4 V6 off road with tow package. I tow my boat which boat , trailer and gear is about 3500lbs. My question - when towing should I drive with the tranny in D or should I drop the selector down a notch? I always tow in D and the truck tows it no problem in the mountains and on the level. It tows so well its almost like I’m not towing anything. I didn’t see anything in the owners manual concerning this.

 

I think you will be ok towing the way you are however, why don't you pick up a scan gauge II. I drive by mine and it is a comfort for me just to watch my tranny temps. Even on a small incline the tranny temp start to go up but they come right back down on the decline and level driving.

 

I believe the proper way to tow is by bumping it down one gear to 4 instead of D.

 

If you have a gauge that tells you what your transmission fluid temps are then towing in D is fine, as long as you keep an eye on the temps and kick it out of D into '4' if they start climbing. D lets the transmission shift into overdrive, which means that less fluid is being pumped through the transmission cooler due to the lower RPM's from the torque converter. The less the fluid moves through the cooler, the hotter it gets. If it gets too hot, it breaks down and doesn't lubricate as well, which causes damage (chart below). However, if the transmission is shifting in and out of overdrive a lot, lock it into 4, regardless of transmission temps.
So if you don't have a gauge (digital; needles aren't a whole lot of help for specific temps), tow in '4' to be on the safe side. The extra gas is a LOT cheaper than a new transmission.

 

The Tacoma owner's manual is pretty explicit about towing in '4' vs. 'D' to prevent constant shifting and transmission overheating. The stock transmission cooler is pretty tiny on our trucks, so I'm inclined to believe it is a well founded recommendation.

 

Thanks for the info. I didn’t see anything in the owners manual about this but I’ll take another look. I live in the California Sacramento Valley and during the summer temps are often 100 and higher. I think during hot weather and on hill/mountains towing I’ll drive with it in the 4 position.

 

I have an ultragauge and in regular flat driving, the trans is at about 135-165 and climbs to 195 when going up inclines for a period of time but comes back down right after. When towing depending on temps, I've seen it no higher than 210.

 

Do not tow in D !

 

This is an old thread but I was looking thru the owners manual today and accidentally found where it says not to put it in D when towing. It’s buried in a section called towing tips.