Overdrive/speed question

Ive got a 2014 V6 double cab 4x4. I make frequent 300 mile road trips from April to November (every couple of weeks) and here in SD/ND/MN the wind can really get to blowing. When I'm driving against a steady 30-35mph wind, is there any harm in simply taking the truck out of D and driving in 4 for extended periods of time at 80mph? Yes, that's the speed limit on the SD interstates (70/75mph in MN/ND). I know gas mileage will take a hit, but is it ok otherwise? Thanks for the advise.

 

It won't hurt the truck at all, but pushing the truck through air at 110+ mph spinning north of 3000 rpm... I have this mental picture of a fuel pump flushing like a toilet . The short overdrive in the six speed 4.0L combo taught me quickly that the motor really likes fuel when it's spun up. Even at 2700 rpm (sixth at about 75 mph iirc) that was around 15 mpg if I didn't get a tailwind. Never tried it in 1:1 at highway speeds because the torquey bugger was happy to use 6th all the way down to 35 mph.

Does it kick itself out of overdrive in that wind?

 

Yeah it will kick itself out of overdrive. And the rpm's will instantaneously skyrocket for about four seconds and then it'll drop back into overdrive (to be clear, this is running on cruise control). It'll stay in overdrive until the incline changes a few degrees again. Then it'll happen again. I know this is somewhat common in TACOMAS (and I'm expecting a lot out of her at those speeds). But it's exaggerated and frequent with a strong headwind. Haha The solution is to simply slow her down a bit but sometimes I get anxious. Just wondering if it would hurt anything. It's the repeated rapid rpm increases that concerns me more than just driving steadily at a higher rpm.

 

if you find its hunting for gears... between 4th, 5th and 5th lockup..... pop her in 4th so the torque converter locks up, your trans will thank you very much.

zero harm to the truck.

 

What is 5th lockup? And I'm not familiar with the torque converter. I'd be grateful for an explanation.

 

so you have the 5 gears in the transmission, 1 - 5.

Then you have the torque converter, which is the "viscous clutch" between the transmission and engine. This allows you to come to a stop still "in gear". The problem with a torque converter is that by nature of it being a viscous clutch it slips, meaning the input rpms is greater than output rpms... this means loss in the form of heat etc.

To combat this all modern cars have whats called a lockup clutch inside the torque converter, that locks up the input and output shafts so they spin at exactly the same rate, meaning no losses due to slipping etc.

On our 5 speed transmissions lockup occurs in 4th and 5th gear ONLY.

You will notice that if you are cruising on flat ground at say 70ish, you will be churning right around 2000rpms. You can roll into the throttle a smidge and watch engine rpms and speed move up at exactly the same linear rate.

Roll into the throttle a little quicker and more, the trans pops out of 5th gear lockup and gives you 5th gear, This spins the engine a little faster, and engine rpms can increase and decrease at different rates than speed, due to the slipping nature. This scenario produces alot of excess heat and is bad for the transmission if ran for long periods of time, and or constantly in and out of a 5th lockup state which will heat up and use up clutch packs etc.

You can get a good sense of the lockup clutch in action if you do the following. From a stop put it in 4th roll into the throttle till you are accelerating at a decent rate (say 2500ish rpm shifts). Watch your engine rpms as you steadily increase. You will notice the 1/2 shift, 2/3 shift, 3/4 shift..... then when you think its done shifting, you will notice the rpms drop one last time, That is the lockup clutch engaging, and you are now truly 1:1 between engine output and trans input. Continue accelerating, move the shifter to 5th (D), as soon as you do so, you will note the decrease in engine rpms due to the taller gear, then shortly after, what seems to be another shift... thats lockup happening again.

 

If I do as you described, and took it up to 80mph, I'd then be in "lockup" at that speed? So I'd still be in 5th, but at a higher rpm than if I'd have just accelerated from 0-80 in D ?

I appreciate the time you put into that explanation. I'm not quite following yet. I'll do some studying and maybe come back with questions. Thanks much @nd4spdbh

 

Putting it in 4th and accelerating just allows you to see what is actually going on. If you left it in d the trans would go all the way to 5th lockup and depending on load etc it might just skip 4th lockup and go straight from 4th to 5th

You have the available spots on the trans. 1st , 2nd, 3rd, 4th, 4th lockup, 5th, and 5th lockup

Lockup simply stops the slippage of the torque converter to provide better mpgs, it is not another gear.

 

So, essentially, you're saying drive with shifter in 4 instead of D when I'm driving in the described conditions. Am I understanding correctly?

 

yes, if you see that the trans is having a hard time staying in 5th lockup, and is constantly hunting between 4th, 4th lockup, 5th n 5th lockup.... stick it in 4, so it cant go any higher.... your clutch packs in your trans, and lockup clutch in the torque converter will thank you. I have seen trans pan temps around 220* when its hunting... as soon as it gets into lockup (4th or 5th) pan temps drop significantly back down to under 200*f.

I have noticed that the trans's on these trucks are pretty smart.... if they cant hold 5th lockup, and you jab the throttle just a bit to get her down into 4th, it will hang on 4th lockup till it senses the crest of the hill / extra load thats going on while the gear selector is still in D.

 

Sounds like a 6 spd would have been ideal for your unique commute. I would leave it in D personally, but driving in 4th won't harm the truck, other than worse mpgs.

 

Thanks for your explanations/advice. I'm starting to follow you now. I know "by feel" what you're talking about when you say to jab the throttle. If I'm not using cruise control, I can pretty much keep it all smooth sailing in D by just sensing when to let up or jab the throttle a bit. I've driven these trucks long enough to pretty much anticipate when she's gonna drop gears and exactly how long she can maintain speeds in different conditions/circumstances.

Often times when I'm using cruise at those speeds and I can anticipate that its gonna downshift, I just place my foot on the throttle, cancel the cruise, reduce speed one or two mph and then I can manually accelerate back up to speed and hold speed manually just fine. Essentially, I just beat her to the punch, and achieve the same objective in a little different way. I'm now wondering if I've actually been playing with the locker without even knowing it.

 

you probably have.

I rarely use cruise control any more, cus i can anticipate the hills etc. If im crusing at say 65, i can roll into the throttle just before it pops out of 5th lockup, and say loose maybe 5mph in speed.... but never have the trans shift... i call it riding the rollercoaster and sticking with a similar throttle input.... mpgs are way better this way.

 

Yep, that's exactly what I was trying to describe. Lose just a little speed but avoid the sudden rpm increase.

 

Using 4 on the highway won't hurt a thing. The 5th gear in these trucks is all but useless except for flat terrain cruising under certain conditions. If the wind/grade/acceleration keeps making the tranny hunt for gears, I say make up its mind for it.

 

I'm going to be making this 300 mile trip again this weekend over the heavily glaciated terrain of north eastern SD and northwestern MN. Per usual, I'm sure I'll be bucking a 30-40mph headwind over the glacial moraines and through puddle lake areas. Yes, all at 80mph. Ha-- and with a queen sized mattress and box spring in the back end with a 20' ladder on top.

I Picked up a new set of ratchet straps and compression straps to keep it all secure (my ego is now telling you that I'm kind of a master at gear placement and securing loads in Tacomas). I spent more hours in college packing my truck for a multitude of adventures than I ever spent on studying.

My fam gives me shit now about it because I'm so precise with the process. I can laugh about it with them when it's all my stuff, but when they call on me to help them with moving their stuff, I do let them know in "a teaching moment" that their packing methods would probably result in 3 separate loads wheras I would have it done in 1 single well secured load-- Because I'm just that god damn good

Whew I got long winded there. Sorry! Back to my point... I'll do some experimenting on the highway with the things discussed earlier in the thread. I'd really like to feel all of this stuff we discussed about 4/4 locked and 5/5 locked, etc. And maybe see if there's a different way of driving That might help me out.

Again, thanks to you that took time to get me up to speed with the valuable information you provided. I'll come back with a report in a few days.

 

You could always change the gear ratio of the differentials. If this is a daily occurrence, it might be the best thing for your truck mpg wise and transmission life wise.