Transmission Temps, Lockup and Tow/Haul

[henryj]

This is a response to a question JohnB asked in my post in the Community forum. I thought starting a new thread here would be a better fit.

My 1500HD has the 300 hp 6.0 L and 4L80-E 4 sp auto. A transmission temperature gauge comes with the towing package in this model. Air flow through the grille is perhaps somewhat reduced because I have a protective cover to stop the hordes of big bugs and also rocks common to western travelers. A magpie is feasting at this buffet in Waterton Lakes NP.


This cover is easy to install without tools and I monitor the temperature during steep climbs, but have never felt it necessary to remove the cover. I also have metric instruments so will just give you reference numbers. The instruments are actually identical to the US ones and the needle rests at the same optimum points--only the numbers on the face are different. On the transmission temperature gauge where the US one has 200 F, the metric one has 95 C and both, of course, are just under the bp of water. A photo of the gauge in the 01 Silverado sales brochure shows the needle resting exactly on 200 which suggests GM might consider this the normal operating temperature.

Towing or solo on level ground with no wind I'm running 1-2 ticks under 200 at 60 mph in od. Driving straight into a 35-40 mph wind on level ground, but in 3rd gear at 55 mph the gauge was 1 tick under 200 in an all day drive. (What was our gas mileage you ask?? 7.7 mpg... OUCH!) On the longest 32 mi. grade where we could still maintain 50-55 mph in 3rd the transmission was 2 ticks above 200. On shorter, but much steeper climbs with 20 mph or less switchbacks the transmission was also 2 ticks above 200. These high temperatures were still 4 ticks out of the red zone so I feel comfortable with that. Engine temperature was also slightly higher than normal in these climbs, but drops back faster after cresting the pass than the tranny temp does. Air temperature was typically in the low 80's.

Tranny temps remain relatively low in normal driving, even while towing, because the torque converter is locked up. The tc creates a fluid coupling between the engine and tranny that provides good performance, but slippage creates heat and reduces gas mileage. For years now typical 4 sp autos have had a feature that mechanically locks the tc to increase gas mileage, but also reduces slippage and heat. On my truck the tc locks up between 55 and 60 mph depending on how easy I'm driving. I can feel this as a 200-300 rpm drop that feels like another shift. Driving into the strong head wind cooled the tranny adequately even though it wasn't locked, but of course helped to kill the gas mileage. Slow mountain switchbacks don't provide enough airflow over the cooler and temps rise. Driving up and down very hilly terrain doesn't give the tranny fluid a chance to cool on the downhill portions before it has to work hard on the next uphill and temps rise again. Adequately sized tranny coolers are found in tow packages and are the main reason one shouldn't tow a big trailer without a tow package. Without a temp gauge the only way to tell if tranny fluid has been cooked is to check the color and smell. If you tow a big trailer over hills without a gauge you should check the fluid every day especially on hot summer days.

Tow/haul mode raises the shift points for better performance and makes them firmer for less slippage and heat. The usefulness of T/H in GM's lesser transmissions depends on the load and the truck. My 2499's travel weight is just under the weight that GM suggests using T/H for my truck. But T/H in the Allison tranny is a very useful and sophisticated feature. I use T/H mostly to keep the tranny out of 4th lockup when I need a few more rpm or don't want it to hunt up and down. Otherwise I often manually shift down to 3rd for a hill climb. I'm not sure T/H locks up the tc, except perhaps on the Allison, because I run the same temperatures whether I climb a hill with T/H or not. I also recall that T/H had a much bigger impact on my 4.8 L Silverado and I used it often with the Aliner. Perhaps the 6.0 L has so much more torque T/H isn't as noticeable.

I'm interested in others experiences too, especially with Tow/Haul as I'm not sure I'm getting the most out of that feature.

Henry

[frank]

Originally Posted by henryj

I'm interested in others experiences too, especially with Tow/Haul as I'm not sure I'm getting the most out of that feature.

Henry

Henry,

I have an 06 2500HD 6.0 auto.

Keeping in mind that factory instrumentation is notoriously inaccurate(!), your trans temps certainly run considerably higher than mine. You say that you are seeing around 200F even unloaded, I have never hit the 200 mark yet even when towing the 2363 in 95F weather uphill. Mine spends most of it's time I believe in the 150 range. Can't say I trust the dash gauge implicitly (and I am a dipstick sniffer), but I think I would try running without the grille cover and see if it makes a difference.

As for tow/haul, I'm also pretty much under the weight GM lists as the tipping point, but I am typically happier with it in t/h mode. With the torque converter, I'm almost 100% positive that I see TC lockup in 4th while in t/h mode. I will try to remember to bring the scan tool along next time I have the trailer out, as I'm pretty sure TC Lockup is reflected in the datastream. I have never seen any 3/4 hunting in that trans even when I pulled the car out to Iowa earlier this year, and then I even had t/h off. I'm thinking that both of my usual towing loads are less weight than your 2499 though.

- Frank

[JohnB]

Henry

Very good post. I will respond to this as I have a lot of info on my prior K2500 Suburan with the 6.0, 4l80E tyranny and a 4.10 rear end towing a T2499 no less...

I did not catch what rear axle ratio you have. What is it?

I'll be back with more soon as I can compare it to my F350 as well pulling both the T2499 and the T310SR

Thanks

John

[henryj]

Yeah, I should have taken the cover off for one day just to see the effect. We have taken the rig to FL without the cover and I can say that under similar driving conditions, I65, the cover makes no difference. But of course I65 doesn't have 32 mi. grades and switchbacks that drop speed, and air flow down. My brother, who was following us in a Dmax/Allison, hauling at least 3000 lb. more had temps. well under 200 in all conditions. His worst mileage into strong headwinds was also 13 mpg compared to my 7.7. I should add that he tows a Titanium which is arguably the best towing trailer out there. He easily got 16 mpg in most conditions.

I don't know either how accurate these gauges are, but am puzzled that GM would photograph one at 200 if that was a problem. That 01 picture also had the gauge oriented with 200 at TDC where "normal" is on all the other gauges. Interesting that they later twisted it so the red zone is at TDC.

John, my axle is 3.73. The combo seems to have a sweet spot at 2000 rpm and that's what I usually run at--60-62 mph. 55 mph is a big pain because it can't decide whether to lockup or not and if it does the engine is lugging so I usually shift down to 3rd if I can't drive in 4th lockup. Then I'm pretty close to 2500 rpm.

Henry

[DF5.4]

When I had my F150 I added an Auto Meter transmission temp gauge. I also added a Hayden transmission cooler. When the truck was empty it would run about 70 to 80 degrees above the air temp. If it was 50 degrees out the trans temp was 120-130. If it was 90 out the trans was 160-170. It would only get up to 200 and above if I was towing the Sunline. I know it's a different TV but 200 degrees sounds high for any auto transmission when the truck is empty.

[Sunline Fan]

John,

Does your trans temp gauge on your F-350 ever move? I was putting strain on that tranny today because I just couldn't keep it in OD all the time, and between that and traffic, the trans temp gauge never moves. Actually the engine temp one never moved either. I would expect it to move some. If it was going in and out of OD a lot, I did shut it off, but it still shifted more than solo.

On a side note, the new Reese head and 1700# bars were excellent! Very stable and it didn't sway much at all. Only downside was the 6.6 MPG (acording to the computer). Used almost all 44 gallons on the 238 mile total trip.

Jon

[andyhirsch]

Unfortunately my Tahoe that I tow my T2670 with doesn't have a tranny temp gauge. From my trolling on various GM truck forums it seems that tranny temps of over 100 degrees above ambient outside temperature for a prolonged time is not good.

[DF5.4]

This is a chart that shows predicted transmission life at different temperatures.

[henryj]

Thanks for the chart--very helpful. So it looks like 175 is the best temp. This is 2 ticks under 200 and what I'm running at most of the time solo or towing except for towing long steep grades. Two ticks over 200 is around 225 and this obviously is not good. I was planning on changing tranny fluid after this trip and this just confirms it. Color and smell are both still good, but even so it's cheap maintenance after a long hard trip at summer temps.

Next time I'm up against a long hill I'll take the cover off too so I know how big an effect it's having.

Henry

[Honda03842]

We have a motorhome and transmission cooling is critical. We do two things: first we have routed the output of the windshield wiper water to the front of the transmission cooler, controling it from a new dashboard switch. This allows it to cool the transmission fluid when facing long hills. Normally the transmission does not overheat on flat runs.

Second we flush the transmission and replace the fluid every 25,000 miles regardless of the color of the fluid.

Also I check the color of the fluid regularly, at least once a week when on the road. If it is ever discolored, replace it immediately, fortunately I never have had to.

On the road with our Sunline in South Dakota
Norm and Ginny Milliard
1982 Sunline 15.5 SB
2004 Honda CRV

[JohnB]

Henery

Let’s compare notes. I had the 6.0, 4L80E with the 4.10 in my 2003 K2500 Suburban pulling my fully loaded with water T2499 weighing in at 6,800# Total GCVW, 15,100 That was a great combo. I miss that truck.

I only carry water at certain parks where the water is well, not great tasting. So that is 382# less normally. Or around 14,700# GCW. The Suburan weighs more then your truck and it only has a 8,600 GVWR to your maybe 9,200#. At least that is the 2500HD

I drop the tranny in 3rd gear, direct drive, tow haul on and tow normally at 60 MPH. The RPM’s if I remember right where around 2,300. It might of been 2,150. I’m now memorizing the F350 speeds and the Burb’s numbers are fading…

I also installed a Torque Convertor (TC) output line temp gage. So since the ¾ ton has the pan temp in the dash I can see both pan and TC output.


On a mild day, 75F air temp, non towing temps in the pan when mid 140 ish. Cursing down the highway in OD. The TC output would be very close to the same. Maybe 5 degrees above. The GM gages are acurate and fairly fast to respond as compared to my digitial one.

Now towing on that same 75F air temp day, in 3rd, the pan would go up to 190F, TC output around 210.

On a towing day of 90 F air temp, in 3rd, the pan would go up to 198 to 200F, TC output around 225 / 226 cursing down the highway.

On a hot day of 85 pushing 90 going into town towing, the pan was 200 and the TC output could go up to 235 when at a pull out from a stop sign and then onto the entrance ramp starting go above 260 for about 3 to 5 minutes then come back down when on the road going. But the pan never went above 200.

This 6.0, 4L80E / 41.0 is rated at 16,000 GCWR. I think your 3.73 might be 14,000. My books are at home and I’m away for work.

Around anywhere in Ohio or Western NY. The pan would not rise above 200. This drive train and the aux cooler just runs that way. The 260 spurts of TC output on stop signs or when ever the TC would slip would diminish when returning to the pan.

If I go to OD, the pan temp drops about 2 to 3 degrees. But then I start shifting at every mini hill so I put it in 3rd and purr up and down, but it runs hotter yet it is not shifting and the fan is running faster. I know this does not sound right, but that is what it does.

I also had 2 bikes on the front of the truck and it would raise the pan temp about 2 degree. Still only 200 as it flutters between 198 to 200

I have the GM shop manuals on this truck, about 7 inches thick, and they do not stated anything about what mileage when towing heavy to change the tranny oil, just change it more frequently. So I did. Once a year I changed the tranny oil and the rear axle. About 8 to 10K towing miles. For me this is cheapo insurance.

Here is the aux trans cooler GM puts on the Suburban, It is a stacked plate type 11” wide, 5” tall and rates at this 16,000# GCWR. GM runs the TC output to the main radiator, then the aux cooler then back into the transmission. I’m really curious on what your 1,500HD has and what a 2500HD has. The 2500HD has the same drive train and is rated the same pulling. But it is a PU in place of a SUV. So it “might” have a bigger aux cooler. See here


Since I change tranny oil every year I set it up the first time to be quick change. See here. This are full port ball valves connected in a 3 way combo and a drain hose.






The 3/4 ton truck has an actual drain plug in the pan, pull it and get out ½ the oil. Then refill with I think it was 6 quarts and put hose in bucket. Start truck with a buddy inside and pump out the other 6 to 7 quarts in the TC while constantly filling quarts. Have all the quarts ready and open to pour before you start. If it get’s ahead of you, have the buddy shut the truck off. When the hose shows bright new oil, it’s over.

The rear axle has a nice drain plug right in the center of the casting and a refill on the side. Again do not have to pull the rear cover.

I do change the tranny filter about every 30K miles, just not every 10,000 miles then it is only the oil or once a year. Since I do this myself, it is only the oil cost. The 1st time I changed it, there was almost nothing in the filter. This was at 40K miles on the truck. We bought it used. The drain plug has a magnet and it only had fuzz on it, no shavings at all.

See here for curious on what the bottom of that 4L60E looks like


And here is the filter


I was concerned about the 200F running temp but after researching all I could find is GM runs it that hot and change often. I probed into adding a large aux cooler but then I was cautioned about it getting to cold in the winter and messing up the shift points. So I left it.

This all worked OK until the day I found it’s real limit. I was bringing the new camper home and camping in the mountains of PA on the way home. TT was empty and GCW 15,000. Well I missed the camp entrance and had to follow a 1 lane road for at least 5 miles until a forest service road came up I could turn around. Doing 30 MPH up hill and the tranny pan went to 235. The TC output was above 260, It stops reading there. Was in 2nd gear slipping the whole time. Never ran out of engine, just tranny cooling. I let it cool down and then went back to camp. This is the turn around where we let it cool down.


Here is the rig on the way out of camp. What a beautiful camp.


The next day I went back out that same road, but now early morning. Regardless, the 235 pan came back, at the same pull off and let it cool down. Then we made it to the end of that 1 lane road and hit the highway heading east to Ohio. That was the easy part… Next was a series of hills that would not give up. They sort of looked like this going down, then back up.


Oh boy. Well it did OK was hovering around 210 in the pan, OK I can make it.

Then the hill that would not give up. It was down in 2nd gear about 2 miles to the top. The tranny hit 245 and the TC output was flashing Hi over 260 long ago. About 500 feet from the top the engine hot came on, Oh boy…. So I took my foot out of it, the engine came down immediately and it down shifted into 1st. We crawled to the top and pulled over. There was a guard rail all the way up and no place to get off. The row of 50 plus cars then zoomed by, we sit there now 30 minutes letting it cool down and took this pic. Counting ones blessing every moment.


From there we hit the interstate and then no problems. Could do 7% grade doing 50 MPH. All was well other then me still sweating out bullets… fomr the "hill". I know a new TV was soon to come but I did not know that soon with just an empty trailer and only 500# more weight then I normally haul around

At home in the flat lands of Central Ohio, I loaded the TT part way until the truck limit. I was at 15,760 GCW on the 16,000# GVWR truck. It towed OK and no heat issues for about 3 months then I sold it. But I knew better then even attempt the hills of southern Ohio.

Now to Jon’s question on the F350. This 6.8 V10, 5 speed Torque shift tranny, 4.10 rear end rated at 21,000 GCWR has no issues period wiht this TT. I put it in tow haul and go. She runs at 1,750 RPM in 5th gear crusing 60 down the highway. My loaded F350/ T310 GCW is 17,500# no water. The Aux tranny cooler on the front of this beast is the entire full width and height of the main engine radiator. I’ll have to measure it. But it has to be almost 30 inches long by 18 “ tall and 1/2" tubes going in and out. This thing is made to pull. Ford has very slow, dumb gages. There are no graduations and no lines of reference. I have no clue what temp it is. And I have yet to see it move while towing or non towing. It does drop down when the truck cools off. Ford says to change the tranny oil every 30K miles I think. It might be 35 but it is in that area on this Torque Shift tranny. They also give me a screw on filter just before it goes in the radiator.

I have a OBD2 scanner that can read out tranny temps, however I have not yet hooked it up while towing to know what temp it is even running. Will do soon.

I hope this helps you.

John

Edit 10-8-08 Fixed tranny number to 4L80E which is what it is suppose to be. And the right 6.8 engine size.... It was a bad day typing...

[Sunline Fan]

Ford does say to change it every 30k. I just did mine (& filter) I think for the first time at 95k. Fortunately for spending half it's previous life as a rental vehicle, I don't think it would have seen much towing.

Is the tranny cooler down there by the fog lights? If that's it, it sure is big!

Jon

P.S. It's a 6.8L V10, not a 6.7.

[henryj]

John, thanks for the info. It is helpful to put my numbers into perspective. Obviously pulling the bigger 310SR put a major load onto the Suburban. I think the lesson here is that even a 3/4 ton truck with good specs can see some pretty high tranny temps when towing a big trailer in the hills. I have an appointment tomorrow to get the tranny and rear end fluid changed. I'll report back on how the old fluid looked.

John, you say in the first line that your K2500 had a 4L60E. Did you mean 4L80E??

The 1500HD was introduced late in the 01 model run and produced until the old style 07s were shut down. I already liked this truck when I bought my 01 Silverado because it had such nice specs, but it was way more than I needed at that time. The 1500HD always came only as a crew cab, 6.5 ft. bed, 300 hp 6.0 L, 4L80E transmission. Beyond that you could choose 2 or 4wd, 3.73 or 4.10 and LS or LT. So it was a pretty nice truck right out of the door. For those who really know their GM trucks... there was also a 2500 4wd with the 1500 body style that was available for a couple of years. It's this truck with which the 1500HD has the most in common despite its 1500 model designation.

The 1500HD has a GVWR of 8600 lb., FAWR 4410 lb., RAWR 6000 lb., payload 3129 lb., GCWR 14,000 or 16,000 lb. and tow rating 8300 lb. or 10,300 lb. The front axle is the standard GM 3/4 ton setup with torsion bars. The rear axle is semi floating and rated at exactly 6000 where the 2500HD is full floating rated at 6084 lb., the limit of the LT245 tires. The rear axle is the biggest difference I can see between the 1500HD and 2500HD. The wheels and tires are the same, the springs have the same number of leaves and the shocks are the same--I'm getting some new Bilsteins tomorrow too and the part no. is the same for both trucks--and, of course, the ride height is the same.

I took my truck off the lot and had to take a 3.73 axle. My dealer searched all over ON and couldn't find a 4.10 in either 2 or 4wd so it seems GM mostly shipped a 3.73 and those who insisted on a 4.10 bought the 2500HD. At that point I was buying the 1500HD to tow the 2499 so even the 3.73 provided a reasonable cushion.

I also have the 11 x 5 tranny cooler even with my 14,000 GVWR. Since the Sub., the 1500HD, and 6.0 L 2500HD have the same max. 16,000 GCWR, I suspect the 2500HD will also have the same size cooler. In fact, I wonder if the 1/2 tons might have that cooler too, especially with a tow package. The 1/2 tons' 4L60E has about 2 qt. less fluid so likely could use the extra cooling.

Henry

[JohnB]

Originally Posted by henryj

John, you say in the first line that your K2500 had a 4L60E. Did you mean 4L80E??

Henry

Henry, yup your right. I'm having a senior moment.... The 4l60E is the 1500 tranny. The 4l80E fits the 6.0 engine the 3/4 ton Burb and PU.

The 4L85E mates up in the Burb with the 8.1 monster big block and in the PU. The Duramax has the Allison. I'm even more curios on the aux cooler size in the 8.1 or the Duramax. They are both rated up there in GCWR. I would hope the cooler is bigger.

The new 2007 K2500 Suburban redesign has a 4L70E. Why did they down size the tranny? Weight, cost???

Thanks for the info tide bits on the 1500HD. I knew it was close to the 2500HD but never realized that close. As you know, that should mate well with your T2499.

Interesting post. Thanks

John

[JohnB]

Originally Posted by Sunline Fan

Ford does say to change it every 30k. I just did mine (& filter) I think for the first time at 95k. Fortunately for spending half it's previous life as a rental vehicle, I don't think it would have seen much towing.

Is the tranny cooler down there by the fog lights? If that's it, it sure is big!

Jon

P.S. It's a 6.8L V10, not a 6.7.

Jon

Boy between the GM tranny mess up Henry found and the Ford engine size.... I must be loosing it Thanks for keeping me straight.

Tranny cooler by the fog lights. Well all V10's are not created equal and maybe the aux cooler as well.

This summer I was camping with a Buddy who had a 2005 V10 EX. We lifted the hood on both 2005 trucks and looked. Holy cow what a change. Ford never put the new 2005 V10 upgrades into the EX like they did the Super Duties. Talk about a redesign.... The EX was it's last year and the Super Duties where on the rise. The entire top of the engine intake manifold was totally different. Plus a lot more I do not exactly recall. The 3 valve came in 2005.

So I do not know what your aux cooler looks like. Crawl under the truck, find the TC output and return lines coming from the tranny. They should go to the bottom of the main radiator then out of the radiator and into the Aux cooler and then back to the tranny. Mine is the full size across the main engine and AC unit coil. I could not believe it, it was so large. I'll pop a pic this weekend.

John

[rich2500]

jon if your ex has a factory tranny cooler it will be between the ac condensor and the radiator at the bottom,I would highly recommend some type of a tranny temp gauge because the 4r100 tranny(same tranny in your ex ) in my truck likes to heat up when being worked, especially when the ambient air is warm,I could easily hit 210 plus pulling hills over the summer,I have since added a second cooler out in front of the ac condensor behind the grille and that pretty much keeps my temps below 200deg. now.I'm reading my temps with a scangauge 2

[Sunline Fan]

If it stops raining tomorrow like they say, I'll try to run out to the parking lot and get some pics. I don't have anything to lay on the ground with here, so it'll have to wait until the weekend until I can get under there.

Yeah, for the longest time I thought my mom's '05 had a 3 valve, but then we were camping next to a guy who was a Ford employee and had a '00, and he came over, we popped the hood, and he said, nope, that's not a 3 valve.

Rich, is it possible to get a unit that can track the trans temp as well as gas mileage and other things all in one unit?

Jon

[rich2500]

yes jon the scangauge(with x-gauge) is exactly what you would be looking for,just plug it in under the dash and done,for tranny temps you do have to enter a series of numbers to enable that option but it's very easy,I love mine,I never really have to look at my instrument panel because everything I need to see I have displayed on the scangauge,rpm,mph,tranny temp,and cylinder head temp.
http://www.scangauge.com/