kkriskal

Hello Experts, I have a brand new 2016 Tahoe and today I visited Pikes Peak and while coming back downhill, I used 4 Low in the transfer case as the vehicle was going way too fast going downhill and had to use lot of brakes. So, I stopped, put the transmission in Neutral, shifted to Four wheel drive Low and kept my speed within 35 miles (manual says to keep it below 45). However, I missed reading this earlier that we should Not use 4 High Or 4 Low on dry payments, so want to know if I have done any damage to the vehicle. As soon as I came down the mountain, I stopped, follow the procedure and shifted back to Auto. Have I still done any damage because of using it in 4 Low for the entire downhill which is I think about 19 to 20 miles at speeds between 15 to 35 miles. Please help

My Vehicle Details
2016 Chevrolet Tahoe LTZ (Has only 200 miles on it now)
4WD
5.8 V8

Regards,

Kalyan

cleveland63b

no it shouldn't have caused any damage if you stayed at those low speeds, however you shouldn't be using auto mode for normal daily driving

kkriskal

Hello cleveland63b,

Thank you so much for your reply, brings a lot of relief and I will sleep peacefully. Regarding the Auto Mode, I asked the service team and they said I can use it but the only problem is that it will have a lower fuel economy but does No harm to the vehicle. Kindly let me know if that information is incorrect. Thanks.

SWHouston

Nothing has been said that's too far from reasonable.

Customarily, we keep our top speed in 4WD-LO at/below 30mph.

The use of Auto 4WD is usually used for varying surfaces
that change from dry to wet to ice to snow.

Also, one need to be aware when using the Auto mode, of the sudden
engagement (not dangerous, but can be quite surprising).

The recommendation of not using 4WD in any mode on dry pavement
(other than Auto) is because of the locked front differential. The locking
causes a considerable drag when turning. This will increase wear on the
front Tires, and cause a reduction in fuel mileage.

Exception:
I have often/briefly used 4WD-lo on dry pavement when maneuvering large trailers.
The increased gear ratio offers a very smooth and precise/seeming effortless
control of positioning.

Use it or Loose it:
Well not quite, but, the most common problem with not being able to shift into 4WD-lo
or being quite sluggish in changing, is not using it.
It's highly recommended that at least, once a month, that you change to 4WD-lo,
and drive your vehicle about a mile or so. Keeps things operating better.
For this brief "exercise", dry pavement is acceptable.

All in all:
I'll never buy another vehicle that doesn't have it !

kkriskal

Hello SWHouston,

Thank you for your reply, make me a lot more relaxed. I will consider this as the once a month usage (a lot more that what you recommend) but will run it for around a mile from next time. Thanks again, I am so relieved to know that No harm is done. I was so worried because this is a new vehicle and I was kicking myself for using it the wrong way. Thanks again.

SWHouston

You're sincerely welcome

I have a question though...
Where did you get that 45mph number for 4-LO !?
That seems extremely high. I think that would put your RPM up over 3000 ! That seems excessive to me. I've just never run an engine that fast (in 4-lo), without a fair load on it. Which would not be present without towing or going up a very steep grade.

kkriskal

Hello SWHouston,

The 45mph limit is mentioned in my owners manual, here is the link to the online version for 2016 Tahoe, please review page 263.
https://www.chevrolet.com/content/da...ers-manual.pdf

SWHouston

Ok, I saw it, but...
I just don't agree with that. Given what speed the Chain is running in that small
space, I can see problems arising. I'm still recommending not to exceed 30 mph.

PS:
This is not the first time I've disagreed with GM, and several other manufacturers
for various reasons.

kkriskal

Hello SWHouston,

Thank you for the additional inputs, I have learnt my lesson now and will never use 4 Low on dry pavement. However, to give you a background, this is what happened during the downhill drive.

1. Started in Auto with Manual and the range in 2, however had to use the brakes a reasonable amount of times
2. After around 4 or 5 miles, there is a mandatory brake inspection and after the reading, I was warned that the temperature was 470 and they also said anything over 300 is dangerous so asked me to use something that would help with engine breaking more
3. So I rested the brakes for about 20 minutes to cool it, then put it in 4 Low and drove the rest of the way down.
4. I was mostly between 15 to 27 mph but on certain small stretches where there no cars in front and it was a steep place, the car sped to speed between 30 and 35 and I would immediately slow it down by braking and get it back to around 20, tried to use the brakes a little less cause of the overheating warning I got from the inspectors. But the 35 was only for a short burst of 100 to 200 meters here and there.

Since you have highlighted that this speed can cause problems, would I have damaged anything? today I drove to Denver (around 80 miles one way) and back and it ran absolutely fine in 2WD High (now that I have learnt what to use for regular driving so no more Auto unless there is snow or ice). I tested the 4 High and 4 Low and it switches properly, didn't have the heart to drive it on dry pavement and test it. So again have I done any damage or if I just be careful in future will all be fine. Kindly provide your expert opinion. Thanks again for being so patient with me.

cleveland63b

driving in auto means you're driving with the front axle engaged and the transfer case in 2 wheel until it is needed. In my opinion the auto mode shouldn't even exist, you either need it or you don't.


Being in auto will cause things to wear out faster than intended and also reduce your gas mileage. The owners manual will also tell you to only use it in "varying" road conditions .