Transmission Temps - how hot is too hot?

[migizi]

My Setup:

2015 Suburban LTZ 4x4

5.3L with 3.08 gears

standard trailering equipment (from factory)

 

dos NOT include the factory integrated brake controller

I added a Tekonsha P3 brake controller

 

I am pulling a (new to me) travel trailer that has a dry weight of 5091 lbs

I also have a weight Distributing Hitch and a single anti-sway controller

 

According to the 2015 GM Trailering Guide, my tow capacity is 6000 pounds 

(I thought my tow capacity was 8000 and felt pretty confident when I acquired that trailer, but then I found that GM trailering guide after the fact   )

this puts me at 85% with NO payload added.

 

While pulling the trailer home, (about 30 miles from place of purchase),  I really babied the suburban. I used the trailer haul mode and kept a very close vigil on the transmission temp (bordered distracted driving  )

my normal transmission temps were 190/195, and when pulling it was running close to 210 (outside air temp 85).

 

Here are my concern/question(s).

 

 

How hot is too hot for the transmission?

What temperature will trigger the transmission overtemp warning?

How does this Suburban protect itself? (limp mode at a specific temp?)

How do I negotiate a fairly long steep hill?

At what temp should I take action?

 

 

[diyer2]

210 is not unheard of.

The trans  fluid can handle it.

You could add a bigger external trans cooler.

Change your trans fluid more frequently.

Long hills pick a gear that keeps RPMs from being excessive and take your time.

I pull grades a lot living in the Colorado mtns. 

I do the things I mentioned and haven't had any problems when towing.

 

[Grumpy Bear]

The factory fill is a Group III fluid but it is still a mineral oil. Any of the major transmission builders would tell you 180 F is that fluids practical sustained heat limit. I found it curious that GM installed the 192 F thermostat and removed mine after observations that ever while I don't tow my transmission fluid temperatures would reach over 225 F on a hot day at Interstate speeds. Maybe I had a faulty stat but chances like that I will not take.

 

With mineral oil varnish forms at 220F and by 240 F it is no longer about the fluid...it's about the seals. They will start to harden. Neither of these things happens with one punch but it is the repeated trip to that zone the kills both the fluid and the seals. By 260 F the clutches will start to slip. Yes even first time.  Maybe the Group III fluid will take a few more degrees, like 10 - 12 F or so, but no fluid will protect the seals and clutches beyond that 240 F point so taking action before that seems prudent, don't you think? 

 

As mentioned by dyier2 more frequent changes are in order and that will limit damage to the box from 'cooked' fluid but it will not do squat for the seals. I can't say that enough. His advise for an external cooler in addition to is sound as is the remainder of reply. He tows allot in a pretty tough place for it. He's done well with his. I changed mine at 50K with very light service and it had already begun to turn dark. 

 

It does have a 'limp' mode and that trigger is pretty high and I don't recall but maybe 1SLOW1500 will visit this thread and weight in. He has eyes inside the TCM (tuner). It's like the old idiot lights. Comes to the party after it's game over. 

 

There are some other things a guy can do to provide some insurance and to ease maintenance like a transmission pan with a bit more capacity (slows heat build up and aids in temperature recovery) and a drain plug (PML pans can do both) and using a better fluid like AMSOIL or Red Line D6. Neither is a mineral oil. They are PAO/Ester blends that have a practical sustained heat point just about the same as seal failure if the fluid fill is completely this group. 

 

Whatever you decide enjoy you truck, your trailer and the experience. 

[migizi]

I had an additional (large heavy duty) trans cooler installed (yesterday) and took the travel trailer for a pull today. I got the same transmission  temps ?.. so  now I’m even more  confused.

 

210+ is too hot (even in tow haul mode)

added aux transmission cooler

still getting same trans temps 

[Black02Silverado]

Don't know how old this chart is or most online for that matter but it gives a good idea on how heat affects the fluid and transmission.

 

[davester]

Did you plumb the trans cooler so the fluid first goes through the radiator, then through the trans cooler, then back to the transmission?

[Grumpy Bear]

Did you remove the factory 192 F thermostat? The factory thermostat hasn't a minimum flow bypass so no matter how large the cooler the trans can't get cooler than it's set point. Improved racing has lower trigger stats. Also what davester said.  

[swathdiver]

On 7/14/2019 at 8:02 AM, migizi said:

My Setup:

2015 Suburban LTZ 4x4

5.3L with 3.08 gears

standard trailering equipment (from factory)

 

3.42 gear would have given you the higher towing capacity and the accessories that come along with it.  Does your truck have an engine oil cooler plumbed into the radiator?  How about an external transmission cooler just behind the grill?

 

For whatever reason, GM added a thermostat to the transmission so that they heat up faster and maintain a more consistent temperature I guess.  Whatever, get rid of it, especially if you added a bigger cooler.  Also make sure it is plumbed correctly, seen that on these forums more than a few times.

 

On the previous generation, the computer throws a warning when the temperature climbs above 266 degrees and throws a code and tells you to pull over at 270.  The shop manual also says that towing should be done in 4th gear.

[migizi]

Update:

 

With the added Aux Transmission cooler installed (in front of the radiator). I made the trip...about 700 miles round trip.

1/2 freeway, 1/2 county roads. A fair amount of hills, and road destruction.

 

The transmission temperature fluctuated between 195 and 200 (according to instrument cluster gauge).

The only time it seamed to creep up to around 212 or 213, was when I would stop at intersections, exit ramps ext...and this did not happen every time. 

 

The real difference I noticed was with the added transmission cooler, the transmission temperature would not creep up as often, and recover sooner. It should be noted the engine coolant temp remained rock steady at 210.

 

So I am going to conclude these temps to be normal for my setup...??

 

 

 

[Grumpy Bear]

50 minutes ago, migizi said:

Update:

 

With the added Aux Transmission cooler installed (in front of the radiator). I made the trip...about 700 miles round trip.

1/2 freeway, 1/2 county roads. A fair amount of hills, and road destruction.

 

The transmission temperature fluctuated between 195 and 200 (according to instrument cluster gauge).

The only time it seamed to creep up to around 212 or 213, was when I would stop at intersections, exit ramps ext...and this did not happen every time. 

 

The real difference I noticed was with the added transmission cooler, the transmission temperature would not creep up as often, and recover sooner. It should be noted the engine coolant temp remained rock steady at 210.

 

So I am going to conclude these temps to be normal for my setup...??

 

 

 

Your water thermostat has a trigger temperature of 207 F and your primary transmission cooler, being the hot side radiator tank the results look about right with the transmission thermostat still in play. 

 

With the factory transmission cooler routing it is actually a heater UNTIL the transmission fluid temperature exceeds the coolant temperature and then it becomes a cooler but it can never cool below the fluid below the water temperature of the hot side tank. That was their plan anyway. The problem is, the factory transmission thermostat does not have a minimum flow bypass and has a trigger temperature of 192 F. So it sets the floor on the temperature and now your second stage cooler is setting the ceiling. 

 

There is a cooler water thermostat for this motor from GM that is used in the Corvette/Camaro motors about 10/12 F cooler that will lower the system temperature more and requires no re-programing. IPSCO also has an inline housing that will allow use of the standard 54 mm thermostats. 180 F is a great choice for your type of work. It splices into the upper hose. You remove the guts from the factory unit if you use this one. Again no programing required. 

 

Thing is with the factory transmission thermostat still in place it will only hold it more closely to the 192 F set point. Cutting the peaks off and aiding in recovery times which is still good. You can get this cooler yet, if you like, but I'll stop here until you decide what if anything is next. 

[migizi]

Bypassing the Trans Temp doesn't sound like something I want to dig into (at this time), but certainly nice to keep that as another option....

Installing a cooler water thermostat for the engine sounds like a feasible mod to improve the temp of both the engine AND trans.

 

I understand the pros of the cooler water thermostat, (engine and trans both influenced), but what might the 'cons' be?

[Grumpy Bear]

6 hours ago, migizi said:

I understand the pros of the cooler water thermostat, (engine and trans both influenced), but what might the 'cons' be?

I run a 170 F in mine and can't tell you of a single negative effect it has had on my truck. 180 F use to be the OEM Gold standard for decades. 

[migizi]

New problem...

got back from trip and since the trans has 60,000 miles since last fluid change (not flush), I decided to have it done.

on way home from dealer, the transmission now shudders from 2nd gear up (6 speed),

 

back to dealer in morning 

[migizi]

CORRECTION - after reading the service document, I realize a fluid flush was done and not a fluid change...

 

Here is what was written:

 

"

Perform Transmission Flush Maintenance

Added cleansing agent to dissolve and suspend gum and varnish buildup throughout transmission. Completely flushed old fluid and contaminants and exchanged all transmission fluid. Added Fluid conditioner and ensured proper fluid level

 

13 88862156 Fluid 8.8 N

"

 

So I'm hoping there is still contaminated fluid that remained and that another full flush will correct the problem and there is no (permanent) damage.

 

 

[migizi]

Well the jury has convened and its bad news.

The Torque Converter Schmidt the bed.

So I am going to replace both the Transmission and Torque Converter.

 

I have shopped around a little and the average cost is $2500 (plus-minus $400) for a 'remanufactured' transmission, not sure if Torque Converter is included in every search, plus labor and misc, puts me at $4500 average. Warranties are all over the map. Not entirely happy with the places I have contacted today- too many attitudes, too busy to discuss any detail, bad reviews, or just not professional over the phone. 

 

I'm going with my dealer who has always given me top notch service. I'm looking at $5100 for a GM Certified replacement Transmission and Torque converter installed - 3 year 100,000 mile warranty. they will provide a 2019 GMC Sierra Pickup as a loaner - could be 1-2 weeks..

 

We often try to justify our choices and actions. Here is mine...

Had I taken the advice of the masses and left the transmission alone, I would not have this expense. Replacing all the transmission fluid at once is seldom met with triumph with todays transmission. And I can now be added to that statistic. However, over the past 5-7k miles, I have noticed a harder than normal down shift with second gear. I even had the dealer do a relearn reset and did not notice any improvement.  So this transmission had had an issue simmering for a little while...and now that I have subjected it to a heavy tow, and immediately did a full flush - I just exasperated any potential transmission problems. I must now assume responsibility and except my fate. .

 

 

 

_{On the bright side, "I saved a bunch of money on my car insurance by switching Geico"} - NOT