2015 Chevy 2500hd gas, noise when going up moderate hills

[goduc]

You truck shouldn't be staying in 5th with only towing 3800lbs. You need to let up on the gas pedal to let the rpms to drop and that should get you into 6th gear. I have the same issue when towing with my 12 2500 CTD when using TH mode. TH mode wants to stay in gears longer. Sometimes I realize I've been stuck in 5th and have to let up on the gas a bit to get it to shift up. Me personally I only use TH mode when accelerating. I hate it when on the road. I hardly shift down anyway with the CTD and 9000lbs. And that's in the mtns and hills of Oregon. I just stick it in 5th on the slower mountain roads when running 50-60mph.
To the OP, once you get up to speed out on the hwy, try disabling TH mode and just use the shift selector on the gear shifter. You should be able to stay in 6th on most flat to low hills. Then when you get in situations where it wants to shift back and forth drop it down a gear and stay there till things even out. I look at these new automatics with the select shift feature as a manual without a clutch. I always use the select shift to put myself in the right gear.


Also that 6.0 needs to wind out to make it's peak TQ and HP. Nothing wrong with running 2250 rpms all day. It's also normal to hit 3000-4000 when climbing some steeper sections or roads. I would be concerned though about only getting 8 mpg when not climbing. You should be in the 10mpg range with only 3800lbs.

[mike.t]

I would rather enjoy the scenery than spend time going up and down hills/mountains manually shifting the automatic trans.

[RubberNail]

Several things here. First, most probable cause of noise increase is the radiator cooling fan kicking in to cool the engine, which is going to heat up anytime you strain the engine. That happens on my GMC 2500HD Diesel also, as well as in my Chevy 4500 6.0 gas class "C", and it can be serious noise similar to dropping a couple of gears. Second, on tow/haul mode. Check your owner's manual. Tow/haul changes several operating parameters. Shift points are just one. As I remember the owner's manual says you should seriously consider using tow/haul when your rig is at or above 75% of the GCWR. What I notice most while towing a 5't with my diesel PU is that the transmission runs cooler in tow/haul. Third, I do better using the manual shift mode when I'm in moderate pull circumstances (= moderate hills, not mountains, or strong headwinds). If mountainous, but not sustained grades (sustained is 2 miles at 7% more or less) I generally come out ahead letting the tow/haul work. Flat pulling with no headwinds, Tow/Haul offers nothing but decreased mileage, even at full GCWR.

[bluewoo]

Watch your trans temp go up driving local with out using T/h mode - common sense.

Toyota states it also increases P/S pressure when in T/H mode.

I use it and pay more attention to everything else..............

[goduc]

Guys he's only towing 3800lbs. His trans or cooling temps should hardly go up. If he's getting that hot that the fan kicks in the maybe he should take it back to the dealer and have them run a scan on it. I find it hard to believe that a 2015 3/4 ton towing 3800lbs has a hard time staying cool enough that the fan needs to kick in.

[jamesarnold]

I don't know anything about this particular engine and you don't really describe the noise. But if the noise is a clicking or knocking sound I would suspect detonation. A higher octane gasoline would solve that.

[bluewoo]

Originally Posted by goduc

Guys he's only towing 3800lbs. His trans or cooling temps should hardly go up. If he's getting that hot that the fan kicks in the maybe he should take it back to the dealer and have them run a scan on it. I find it hard to believe that a 2015 3/4 ton towing 3800lbs has a hard time staying cool enough that the fan needs to kick in.

True but I see it as surface area and wind resistance vs weight causes more work on our TV. My Toyota get 8 -10 towing 4-6k my Friends with 5vers get 8 running Chev gas 2500HD gas loaded or not. But we all know there are so many other factors too.

I hear the same thing on this video from Fast Lane trucks.
Go to time 25:57 - 26:32 you can hear the cooling fans kicking in on this video.(RAM)

Chev is not as loud @ 2:46 you can hear the fan(s) kick on despite the talking.

https://www.youtube.com/watch?v=GabbyiBSfYw

[bluewoo]

Originally Posted by jamesarnold

I don't know anything about this particular engine and you don't really describe the noise. But if the noise is a clicking or knocking sound I would suspect detonation. A higher octane gasoline would solve that.

Anything is possible that's for sure.

[aceinspp]

Originally Posted by wbdavey

Verret - I'm going to disagree that the torque converter is unlocking, if that was the cause of the noise increase the engine RPM's should change at the same time. I also disagree with not using "tow/haul", why did the manufacturer put it on the truck if there wasn't some benefit while towing? Now for the cause of the noise, IMO you are hearing the engine cooling fan which is thermostatically controlled. Next time it happens, closely watch your coolant temperature and I'll bet the temp goes up as you start to climb the hill and then comes back down shortly after the new noise starts.

You might want to read the manual when it comes to using tow haul mode. It's not needed as I stated. Wast gas for one thing when not needed. I have never had a issue with any of my 5 Chevy truck trannys using as I mentioned. Of course some folks don't use common sense ether. Later RJD

[verretcat]

Thanks to all who have responded to my question. I have a couple of responses to questions/comments. The truck does get into 6th gear, but usually only going downhill. I have about 4,000 miles on the truck. I did record the sound, but it is hard to hear. I have attempted to attach a file with the recording. My typical mileage without the trailer is about 15 mpg, combined driving. From everyone's comments, I will watch the water temperature better, but every time I did look it was at 210 degrees. I will probably use the tow mode only in areas with steeper inclines.

[ebemis]

Hey there Verretcat...I can offer only what I have experienced.

I have a 2012 Suburban w/ the 5.3 liter Vortec and the six speed transmission pulling my ROO 233S. LOTS of surface area on the front causes a good chunk of drag and for me to hit sixth gear even in Florida is rare.....I can do it with a tail wind on FLAT sections of interstate or slight downhill grades. I ALWAYS run in tow/haul mode even though my owners manual states it is really only needed for "heavier loads" but it doesn't state what that is. I have paid much attention to as many posts about towing as possible for fear I needed a diesel (many will jump that way immediately) but in my experience..... your stated RPM level and shift pattern on the hills is completely normal. I leave Florida about once a year for NC and the I-26 climb out of SC into NC has been the most stressful climb...I tend to run up to ~3000 rpm +/- and down into 3rd gear, sometimes even second before I top out that climb. Engine temps have jumped from the normal 210 to ~235 with tranny temps ~225 when it is full blown summer and 96 degrees with nasty humidity. All readings return to normal once climb subsides and my shift pattern and RMP goes back to normal as well. Hard to say what your noise is, my shifting occurs prettly cleanly and i DO hear LOTS of Fan noise as the loading increases on the drivetrain.

All my service checkups return no issues and I consider the truck to be a solid performer, in my experience and limited knowledge, the higher RPM's are a necessity in the gasoline engine and nothing at all to worry about. The longer period of time you run at the 3K range or higher the larger increase in noise and temperatures you will experience.

All over Florida and Georgia I run 2250-2800 rpm +/- depending on winds/grade/traffic and I have more than 10K miles of towing with this setup, truck still runs like a champ and never seems to mind hooking up the trailer and moving along. The SMARTEST and BEST thing you can do is relax and do not even attempt to maintain traffic speeds, ride you 60-64 mph range in the flats and watch the RPM's on climbs and IGNORE your speed...let the truck do its work without bustin' a nut and then once your setup at your favorite campsite, have an adult beverage and make mental notes about your drive so you know what to expect the next time.

I hope this helps!

[ebemis]

and PS..by your posted audio clip..all I hear is "normal" exhaust noise...have you noticed when not towing that if you "light it up" and try to get on it the exhaust noise increases rapidly until your speed and momentum begins to level out?

[mike.t]

Didn't think it would go in to 6th in T/H.

[doc73]

My 1500 never would, and the 2500 Duramax does not. I thought it locked out the 6th speed.

[ebemis]

you are most likely correct Mike.t ..... I never shifted my trans to "M" to see if I was in sixth, just know that my RPM's came down low enough that I thought I must be in sixth gear. I truly have no knowledge of what Chevrolet designed the TH switch to accomplish, anytime I try to ask the dealer or any sort of "chevy person" for information nobody seems willing to share "technical data or reasoning" and as an Ex-Navy Nuclear Operator...I HUNGER for technical details of the "WHY and HOW" things happen!

[doc73]

I do not know what it exactly does either... It is a TOW HAUL mode so when I TOW and Haul I turn it on... LOL

Whether I need it or not, i'll take the slight loss in MPG to not blow something up. But I do tow 9,000lbs.

[ebemis]

Seems a reasonable expectation....maybe my owners manual address this, but I can't recall if it did. And of course a google search returns MANY opinion's but I have yet to find a technical GM/Chevrolet document that definitively states "this is what the tow haul mode does..."

And I am RIGHT THERE with you doc73...my feelings are I am towing so it should be on! ;-)

[ebemis]

OH..and for the OP.....my little 5.3 liter chevy I consider doing well when I average 8 mpg over an entire tow trip...I really don't monitor or care where it goes real time, I know it sucks going into winds and up hill, but then again I resign myself to the knowledge that I am basically pulling a billboard behind my truck so what would I expect!

[doc73]

Originally Posted by ebemis

Seems a reasonable expectation....maybe my owners manual address this, but I can't recall if it did. And of course a google search returns MANY opinion's but I have yet to find a technical GM/Chevrolet document that definitively states "this is what the tow haul mode does..."

And I am RIGHT THERE with you doc73...my feelings are I am towing so it should be on! ;-)

I know the manual does, but I cannot remember... EDIT: page 9-39 in the 2500 manual for a 2015..

[ebemis]

FOUND IT!
Tow/Haul is designed to be most effective when the vehicle and trailer combined weight is at least 75 percent of the vehicle's Gross Combined Weight Rating (GCWR). See “Weight of the Trailer” earlier in the section. Tow/Haul is most useful under the following driving conditions:
When pulling a heavy trailer or a large or heavy load through rolling terrain.
When pulling a heavy trailer or a large or heavy load in stop and go traffic.
When pulling a heavy trailer or a large or heavy load in busy parking lots where improved low speed control of the vehicle is desired.

Operating the vehicle in Tow/Haul when lightly loaded or with no trailer at all will not cause damage. However, there is no benefit to the selection of Tow/Haul when the vehicle is unloaded. Such a selection when unloaded may result in unpleasant engine and transmission driving characteristics and reduced fuel economy. Tow/Haul is recommended only when pulling a heavy trailer or a large or heavy load.

SO...it appears GM classifies a "large or heavy load" as one that is at 75% or greater GCWR.

However, I can't find any reference in the OM that claims what happens by engineering design in the transmission. I would LOVE to see a techincal document listing the "change in shift points" and any "gear lockout" or things of that nature...at least I would love to see one from GM that I know is right instead of reading french on the internet! ;-) ..what's the icon for tongue in cheek? ROFLMAO!