First time using 4wd

foo.c · January 5, 2016

There is front axle engage, it's just not the hubs.

Diff does not turn in 2wd.

Diff does turn in 4 auto, which causes the mpg loss.

I had to google it, only the passenger side axle is disengaged in 2wd so the spider gears turn in opposite directions, but the ring gear is not turning.

I'm a bit outdated on my drivetrain tech it appears. Thanks.

Collier11 · March 7, 2017

Hi,

New member here, I used information from this site in the past to deal with a drivers front seat issue on my 2015 Silverado and I am very appreciative of this site.

Approximately 30 days ago I had my truck in at the dealership for an oil change (30K) on my way home I noticed a hot oil smell. I checked under the hood and found what appeared to be new oil on the plastic cowling above the radiator and nearly filling the recessed void where the driver’s side strut nut is installed.

My initial reaction was that my truck received friendly fire from the lube attendant and it was obvious that is was my mess to clean up. After the cleanup I didn’t note any other abnormalities until last week when I noticed oil drops (smaller than a quarter) under the truck. Looking under the engine I noticed that the plastic skid plate was noticeably oily with drips in a couple different areas. I thought about the hours after the last oil change and if it took the residual oil I may have not reached to make its way down to the skid plate?

I took the truck into the dealership today and their response was that I am running the truck too much in the “Auto” transaxle position. This results in the front differential to increase in pressure causing the differential “oil” to be released out the breather which I am told is up in the engine compartment.

It’s my understanding that the color of the front differential lubricant is a greenish-brown. I’m confident that the drips and oil residue I have come across has been engine oil and not the 75-90 weight gear oil lubricant listed for the differential.

Also, I feel justified in the use of the “Auto” transaxle selection based on driving conditions I experience mainly in my 42 mile commute to work that can range from dry pavement to frost, snow, ice, freezing fog and wet pavement this time of year. I questioned why, if I chose, to run “Auto” year around I should expect the differential pressure to be regulated properly without discharging gear oil into the engine compartment. Lastly the mechanic says he sees this all the time this time of year, so I am very curious if any others have gone through this issue before?

Thanks again,

Collier

Thomcat · March 7, 2017

The turning of the front differential/gears creates heat in the axle/differential housing, making the cold snow evaporate and cause the situation your talking about. That's my guess, anyhow.

Also the front axle is turning under power which may tend to kick up snow more aggressively onto heated engine components and exhaust.

sloz71 · March 7, 2017

May want to get the diff oil level checked. A guy I talked to about his 2015 Sierra told me when he went to change his diff fluid for the first time it was under filled from the factory.

Collier11 · March 7, 2017

Service print out states "Front Differential oil condition and level is good at this time". I've read somewhere here that it's a good idea to change the gear oil sooner than recommended, so I may tackle that soon for peace of mind.

I'm still hung up on the issue is caused by driving the truck in AUTO 4WD (according to technician)?

16LT4 · March 7, 2017

If the fluid is overfilled it could conceivably come out the vent and burn off the hot parts.

MaverickZ71 · March 7, 2017

Service print out states "Front Differential oil condition and level is good at this time". I've read somewhere here that it's a good idea to change the gear oil sooner than recommended, so I may tackle that soon for peace of mind.

I'm still hung up on the issue is caused by driving the truck in AUTO 4WD (according to technician)?

How fast are you driving in Auto4WD? I can see where if you drove at freeway speeds for an extended period, it MIGHT vent some dif lube. Myself, I never drive faster than 50-55mph in Auto4WD, and have never had to use it for more than a few miles at a time. But then I'm old school enough to have had my first 4WD vehicles be trucks with manual locking hubs and floor shifters with manual transmissions and 4.10 gears. On those trucks, 4WD low was good for maybe 20mph, and 4WD high was good for maybe 40-45 mph tops before the engine was screaming.

Collier11 · March 7, 2017

How fast are you driving in Auto4WD? I can see where if you drove at freeway speeds for an extended period, it MIGHT vent some dif lube. Myself, I never drive faster than 50-55mph in Auto4WD, and have never had to use it for more than a few miles at a time. But then I'm old school enough to have had my first 4WD vehicles be trucks with manual locking hubs and floor shifters with manual transmissions and 4.10 gears. On those trucks, 4WD low was good for maybe 20mph, and 4WD high was good for maybe 40-45 mph tops before the engine was screaming.

My speeds will range from city driving .. to 70 MPH. The rural freeway I commute to work on is maintained this time of year with de-icing chemicals. Sometimes I'm ahead of the de-icer truck, sometimes not. The road maintenance crew will also treat sections in both directions and then continue in segments. So I'm driving stretches of freeway with multiple road conditions most days this time of year. I took a look at the owners manual and I'm using the AUTO 4WD appropriately for the conditions listed in the manual. It also states not to park the truck on a steep incline with AUTO 4WD engaged (my parking surfaces are flat at home and at work).

Krusty · March 7, 2017

My speeds will range from city driving .. to 70 MPH. The rural freeway I commute to work on is maintained this time of year with de-icing chemicals. Sometimes I'm ahead of the de-icer truck, sometimes not. The road maintenance crew will also treat sections in both directions and then continue in segments. So I'm driving stretches of freeway with multiple road conditions most days this time of year. I took a look at the owners manual and I'm using the AUTO 4WD appropriately for the conditions listed in the manual. It also states not to park the truck on a steep incline with AUTO 4WD engaged (my parking surfaces are flat at home and at work).

Caution

Do not drive on clean, dry

pavement in 4HI and 4LO (if

equipped) for an extended period

of time. These conditions may

cause premature wear on the

vehicle’s powertrain.

Driving on clean, dry pavement in

4HI or 4LO may:

. Cause a vibration to be felt in

the steering system.

. Cause tires to wear faster.

. Make the transfer case harder to

shift, and cause it to run noisier.

Collier11 · March 7, 2017

Further on in the manual AUTO is defined.

Caution
Do not drive on clean, dry
pavement in 4HI and 4LO (if
equipped) for an extended period
of time. These conditions may
cause premature wear on the
vehicle’s powertrain.
Driving on clean, dry pavement in
4HI or 4LO may:
. Cause a vibration to be felt in
the steering system.
. Cause tires to wear faster.
. Make the transfer case harder to
shift, and cause it to run noisier.

Further on in the manual AUTO is defined.

Zipsort · March 7, 2017

Did you ever figure this out? I just got reminded of my problem! I havent driven my truck in 3 months (its parked in a different state). Last time I used it it was really snowy so i turned on 4hi and it was just mooaaaaning and groaning bad. And it smelled bad. No steam I noticed? But def thanks for the reminder.

2015 silverado