Low trans temps

[LTZNewb]

Hi all, this is only my second post and I’m stumped with as to what’s going on. I have a 2011 Tahoe LTZ with the 6L80 trans. I hear a low pitch humming when driving. It’s usually more noticeable between 20-40mph. Sometimes it’s more noticeable between 5-15 mph. Nevertheless, I hear it almost all the time at highway speeds. It’s shifting smoothly, doesn’t seem to be slipping at all, rpm’s are at 1700-1800 @ 70mph, and idles fairly smoothly. I’ve checked my front hubs and they’re all tight. It’s not tire noise. What I’ve been noticing in trying to track this humming down, is that my trans temp never gets anywhere near operating temps. The highest continuous temp I’ve read is 126. Only one time has it reached 156. Most of the time it’s around 115, and that’s with driving some interstate and some in town for an hour or more. I’ve checked my fluid level multiple times hot, and it appears to be at the top of the crosshatch even though the temps are lower than they should be. I’m wondering if:
A. Is there an actual temp sensor, and if so, could it be faulty? I can’t seem to find out anywhere if there even is one.
B. Is there a thermostat that regulates the flow between the trans and the cooler, and could it be stuck open?
C. Am I damaging my trans by driving with too cool of temps?
I just bought this in July with 178k, and am currently sitting at 193k. I just don’t want to grenade my trans.
Any thoughts would be much appreciated. Thanks!

 

[Doubeleive]

Hi all, this is only my second post and I’m stumped with as to what’s going on. I have a 2011 Tahoe LTZ with the 6L80 trans. I hear a low pitch humming when driving. It’s usually more noticeable between 20-40mph. Sometimes it’s more noticeable between 5-15 mph. Nevertheless, I hear it almost all the time at highway speeds. It’s shifting smoothly, doesn’t seem to be slipping at all, rpm’s are at 1700-1800 @ 70mph, and idles fairly smoothly. I’ve checked my front hubs and they’re all tight. It’s not tire noise. What I’ve been noticing in trying to track this humming down, is that my trans temp never gets anywhere near operating temps. The highest continuous temp I’ve read is 126. Only one time has it reached 156. Most of the time it’s around 115, and that’s with driving some interstate and some in town for an hour or more. I’ve checked my fluid level multiple times hot, and it appears to be at the top of the crosshatch even though the temps are lower than they should be. I’m wondering if:
A. Is there an actual temp sensor, and if so, could it be faulty? I can’t seem to find out anywhere if there even is one.
B. Is there a thermostat that regulates the flow between the trans and the cooler, and could it be stuck open?
C. Am I damaging my trans by driving with too cool of temps?
I just bought this in July with 178k, and am currently sitting at 193k. I just don’t want to grenade my trans.
Any thoughts would be much appreciated. Thanks!

Those are pretty good temps in my book, some may disagree but heat kills. Have you looked to see if it has a external transmission cooler?s such as a trucool? The gmt 900's do not have a thermostat like the later models so no nothing would be stuck open. Humming could be several things but the ring-n-pinion is a usual suspect, as well as u joints or rear diff. Maybe even the transfer case if equipped

 

[LTZNewb]

EDIT: I forgot to mention that there are no leaks, and I had the fluid and filter changed 3k miles ago, and the fluid is not exactly red but is translucent.

Those are pretty good temps in my book, some may disagree but heat kills. Have you looked to see if it has a external transmission cooler?s such as a trucool? The gmt 900's do not have a thermostat like the later models so no nothing would be stuck open. Humming could be several things but the ring-n-pinion is a usual suspect, as well as u joints or rear diff. Maybe even the transfer case if equipped

Thanks for responding. It has an external cooler, and have not seen any leaks. I changed out oil in both diffs and transfer case about 5k ago. I hear the humming less when the temp gets the hottest, which isn’t often. I’ve read that the TC’s are notorious for failing at high mileage, and just want to catch any possible damage early so I don’t grenade my transmission. I wanted to get the forum’s thoughts before I inquire at the transmission shop. Thanks

 

[j91z28d1]

next time you get it humming, pop the tranny in neutral and see what happens. does the sound change with vehicle speed or engine revs. give it some throttle while in neutral as well and see if the noise follows engine rpm or. not.

nosies like this are hard to pin people.

 

[Doubeleive]

EDIT: I forgot to mention that there are no leaks, and I had the fluid and filter changed 3k miles ago, and the fluid is not exactly red but is translucent.

Thanks for responding. It has an external cooler, and have not seen any leaks. I changed out oil in both diffs and transfer case about 5k ago. I hear the humming less when the temp gets the hottest, which isn’t often. I’ve read that the TC’s are notorious for failing at high mileage, and just want to catch any possible damage early so I don’t grenade my transmission. I wanted to get the forum’s thoughts before I inquire at the transmission shop. Thanks

Have you checked the front wheel hubs? At 178k its likey the front hubs would be at end of life, just something to consider as well. Average hub life is 160k

 

[Scrappycrow]

nosies like this are hard to pin people.

Indeed, they are. Not long ago, I had a noise in my '88 BMW 535i that I couldn't pinpoint, which didn't respond to turns, throttle on/off, or neutral/in-gear. I was worried it was the G265 transmission front bearing, which is unobtainium, but it turned out to be a side bearing in the differential. I figured out the source when I bought a Steelman ChassisEAR. I linked to the older version I have, which is good for a shadetree like myself, and it's gone down in price recently, but they also have wireless versions. My only suggestion is to use a good set of noise-cancelling headphones with an input jack, as the set supplied is janky, non-noise-cancelling, and doesn't seal well with bigger ears.

Have you checked the front wheel hubs? At 178k its likey the front hubs would be at end of life, just something to consider as well. Average hub life is 160k

I second this. I had an indeterminate whirring that didn't change in response to turning left/right (a traditional test of wheel bearings), but could feel the roughness by hand with the wheel and rotors off. Only one was bad, but it's good practice to replace in pairs (I kept the smooth one for an emergency spare).

 

[Joseph Garcia]

Hi all, this is only my second post and I’m stumped with as to what’s going on. I have a 2011 Tahoe LTZ with the 6L80 trans. I hear a low pitch humming when driving. It’s usually more noticeable between 20-40mph. Sometimes it’s more noticeable between 5-15 mph. Nevertheless, I hear it almost all the time at highway speeds. It’s shifting smoothly, doesn’t seem to be slipping at all, rpm’s are at 1700-1800 @ 70mph, and idles fairly smoothly. I’ve checked my front hubs and they’re all tight. It’s not tire noise. What I’ve been noticing in trying to track this humming down, is that my trans temp never gets anywhere near operating temps. The highest continuous temp I’ve read is 126. Only one time has it reached 156. Most of the time it’s around 115, and that’s with driving some interstate and some in town for an hour or more. I’ve checked my fluid level multiple times hot, and it appears to be at the top of the crosshatch even though the temps are lower than they should be. I’m wondering if:
A. Is there an actual temp sensor, and if so, could it be faulty? I can’t seem to find out anywhere if there even is one.
B. Is there a thermostat that regulates the flow between the trans and the cooler, and could it be stuck open?
C. Am I damaging my trans by driving with too cool of temps?
I just bought this in July with 178k, and am currently sitting at 193k. I just don’t want to grenade my trans.
Any thoughts would be much appreciated. Thanks!

Get the truck to a local shop and put it on a lift where you can get the truck in the air and all 4 wheeles off the ground/lift platform. Have 1 person in the truck and put it in drive and get up to the speeds that you are noticing the sound. Then, have a second person with a mechanics stethoscope listen to all of the drive train parts, one at a time, until the noise is isolated.

I had a similar noise, and using the method indicated above, the shop was able to locate the sound in my front differential. We replaced the front differential with a low mileage used one, and the sound was gone forever.

 

[LTZNewb]

Get the truck to a local shop and put it on a lift where you can get the truck in the air and all 4 wheeles off the ground/lift platform. Have 1 person in the truck and put it in drive and get up to the speeds that you are noticing the sound. Then, have a second person with a mechanics stethoscope listen to all of the drive train parts, one at a time, until the noise is isolated.

I had a similar noise, and using the method indicated above, the shop was able to locate the sound in my front differential. We replaced the front differential with a low mileage used one, and the sound was gone forever.

That sounds like the best idea. I stopped by the trans shop, and he’s going to check a few things out. I’ll request that be done. Thanks!

 

[LTZNewb]

next time you get it humming, pop the tranny in neutral and see what happens. does the sound change with vehicle speed or engine revs. give it some throttle while in neutral as well and see if the noise follows engine rpm or. not.

nosies like this are hard to pin people.

I’ll try that out. Thanks!

 

[LTZNewb]

Get the truck to a local shop and put it on a lift where you can get the truck in the air and all 4 wheeles off the ground/lift platform. Have 1 person in the truck and put it in drive and get up to the speeds that you are noticing the sound. Then, have a second person with a mechanics stethoscope listen to all of the drive train parts, one at a time, until the noise is isolated.

I had a similar noise, and using the method indicated above, the shop was able to locate the sound in my front differential. We replaced the front differential with a low mileage used one, and the sound was gone forever.

Any thoughts on the low trans temp?

 

[Marky Dissod]

Any thoughts on the low trans temp?

For the winter, feel free to block off the air-to-ATF cooler with a piece of cardboard.
The radiator's coolant-to-ATF heat exchanger will keep things warm enough.

 

[Joseph Garcia]

Any thoughts on the low trans temp?

I'm sorry, but I'm not knowledgeable enough in that area to offer you something of value. But other members of this Forum much more knowledgeable than me in this area will chime in.

 

[swathdiver]

Any thoughts on the low trans temp?

I bet your engine thermostat is stuck open.

I took a drive the other morning and it was 50 degrees out. The transmission stayed in the 120s while on the highway. Once I pulled into town, it was about 60 out and the temps in city driving went into the 140s. The external cooler keeps the fluid about 70 degrees warmer than ambient temperature while highway cruising. If your stock cooler is besting that by a lot, then check your engine's thermostat.

 

[mikez71]

Have you looked to see if it has a external transmission cooler?s such as a trucool?

^X2^

Didn't catch if your cooler was stock or aftermarket?
Thought I heard that too big of a cooler can overcool..

Apparently, the temp sensor is in the valve body..

 

[Doubeleive]

"technically" I guess 180deg is the ideal temp, but for someone like me that actually "drives" 180deg is not able to be maintained in any kind of warm/hot environment.
with a stock setup I can make it 180deg in about 2 miles and it just goes up from there. with the exception of cold ambient temps.
I added the tru cool 40k and a deep transmission pan on my vehicles. no bypass valve. and stays a bit cooler but I also live in california the winter temps here are typically not lower than 30deg more than a couple times per year, it might stay in the mid 30's a lot more.
On a recent thanksgiving road trip over the mountains it was in the low 20's and the transmission was hanging around 120 which is fine for me, like I said heat kills and does more damage than cooler temps do.
if you "buy" a transmission and it has a warranty and you take it back a few months down the road because it has a problem, I 100% guarantee you the very first thing they will do is pull the transmission dipstick and smell & inspect the fluid to see if it is "burnt" which is determined by smell and color a dark color means there is clutch material in it, which typically happens when it gets HOT. It also happens from normal wear (over extended periods of time) which is the reason for changing the fluid as regular maintenance. but people are told 100k is the schedule........DERP......maybe if you drive it 35 on sundays only

 

[LTZNewb]

next time you get it humming, pop the tranny in neutral and see what happens. does the sound change with vehicle speed or engine revs. give it some throttle while in neutral as well and see if the noise follows engine rpm or. not.

nosies like this are hard to pin people.

So I was doing 70 on the interstate, put her in neutral, absolutely no humming sound. Gave it 3k rpms and no abnormal sounds. It was really smooth and quiet. So it’s either a differential, transfer case, or the trans.

 

[LTZNewb]

^X2^

Didn't catch if your cooler was stock or aftermarket?
Thought I heard that too big of a cooler can overcool..

Apparently, the temp sensor is in the valve body..

As far as I know, it’s the stock cooler.

 

[LTZNewb]

That’s what I was thinking about the temp sensor. What’s weird is I can’t find anywhere that shows where it’s located, or even any replacement part. ???

 

[Doubeleive]

That’s what I was thinking about the temp sensor. What’s weird is I can’t find anywhere that shows where it’s located, or even any replacement part. ???

it is a sensor inside the transmission, so unless you plan on opening it up I wouldn't worry to much about it. Never heard of one going bad
some people are just lucky, they never have transmission heat issue's even when towing across the hot desert.
on my 00 that thing never went over 180 no matter how hard I beat on it and it didn't have anything special just the regular trans cooler on the radiator

 

[Charlie207]

So I was doing 70 on the interstate, put her in neutral, absolutely no humming sound. Gave it 3k rpms and no abnormal sounds. It was really smooth and quiet. So it’s either a differential, transfer case, or the trans.

Was it humming @70mph when you shifted into neutral?

Where are you located? It's wintertime, and cold air helps keep the ATF cooler, longer, while out driving. It's like 35 degrees here and my ATF temps won't crest 100 degrees even after driving 75mph on the interstate for a half-hour.