Hot GM Transmission

super99

Well-known Member
I have a 98 Chevy 3500 dually to pull my gooseneck trailer. This afternoon I drove an hour to pick up my Oliver 880. Was doing fine until I got into Silvis, Ill. and had to climb a couple moderate hills, the temp guage went up to 300° real quick. We pulled into the Walmart parking lots and set for about 10 minutes with the motor running in park.It got down to 220° and stayed there for a few minutes, so I took off again. As long as it was flat, it stayed in the 220-240° range, Had to pull a couple good hills in Milan, Ill. and she went up to 300+° till we got on the flat. I pulled over again and set a few minutes and it went back down to 220°. It was fairly flat the rest of the way home, and it ran in the 220-240° range. It was 90° this afternoon, The hottest day I have pulled the trailer with it. Did I damage the transmission? I changed transmission filter and oil about a year ago and haven't driven it very many miles since. I think I should change the trans fluid. I'm not sure how big the oil cooler is, but I think I need to try to fit a larger one in front of the radiator and behind the grill. It's a 454 gas, not sure which tranny is in it. It has 3 speeds and overdrive, no tow haul mode. What say ye????
 
I do not have an answer, but a coincidence as I spun a rod bearing in S10 blazer about 35 years ago pulling a trailer up those hills.
 
Did you flush it or, change the fluid, and filter like the engeine oil?, 300 is pretty hot, but if the clutches are slipping, it's going to create a lot of heat. If it hasn't been flushed every 30,000 miles, chances are it's hurt!
 
check the fluid for a burnt smell, if so changethe fluid and filter. i am not a fan of the power flush for your trans, do you have electric cooling fans also? and are they working? you may need to add an aux trans cooler and possible an aux electric cooling fan too. also check your clutch fan if so equipped. what was your radiator coolant temp?
 
If you flush it you get a 100% new fluid, if you change it you only replace about 35% per cent of it,I never see much debris in the filter, the clutch material is usually laying on the bottom of the pan!
 
It has a 4L80E transmission, which is just about indestructable. You were towing in D and not OD, correct? Towing in OD causes the torque converter to shift in and out of lockup a lot, which builds heat. Heavy towing in OD is about the only thing that can kill a 4L80E. It is basically a TH400 with an over drive between the torque converter and rear planetaries. Some of the rear unit parts will even interchange with a TH400.
 
I have a 95 3500 with the 454, and a 97 2500,350,both need to be in D when towing not OD.
 
If it passes the color test, and sniff test you should be ok. If all the fluid wasn't removed when the fluid was changed there may still be enough dirty fluid, too not look real fresh, but still be ok. I would relay on the smell test. Sometimes I wish I had a transmission temp gage, but I am glad I don't, one more thing to lose sleep over. Maybe a temp gage on my ford powered motorhome would be nice. I know that trans got smoking hot at times pulling my Ford Edge. Stan
 
Get the oil and filter changed ASAP . I’ve ran these pans and they are expensive but they help control the heat and also increase oil capacity .
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Transmission pane
 
Remember Allan in Neb? He was a transmission specialist. He once said on here that if you run your trans temp up to 240 degrees the bond of the lining of the clutches start to come off. I believe everything that man said. He was a wizard.
 
I was using Drive, not Overdrive. Engine was running normal temps, just over 200°. I haven't took the grill off to check anything yet, there is a large electric fan behind the grill on the passenger side of the grill, Is that the fan for the transmission cooler? I will check for smell later today. I have a flat rear tractor tire an hour and a half away that I want to go work on before I start on the truck, yes, I have another pickup, I'm not driving this one. Thanks, Chris
 
I don't think GM makes very good transmissions. My work van has roughly 80,000 miles on it since I've had it and the transmission has been overhauled twice. The last time it was done the transmission still experiences a little hard shifting. If I can ever get one I'm going to put an AC Delco filter on it and see if it helps.
 
The fan is for supplemental cooling air for the A/C condenser when stopped. If you were towing in D, I would make sure the torque converter is locking up properly. Get it warmed up and at a steady 60mph in high gear using the throttle. While still holding the accelerator, tap the brake with your left foot, you should see the tach jump up slightly as the torque converter releases. It should set a code and turn on the SES if the converter isn't working, but I have seen stranger things.
 
I have a 4L80 in a 92 Chevy diesel and the transmission is out now for the second time. Never could keep the engine from getting hot. Even put in a bigger radiator. On a 90 degree day pulling a 35 ft. empty trailer would drive two mile and the gauge would be in the red. That is starting with a cold engine, one mile of gravel road and one mile of highway up a 2 percent grade.
 
Pull the upper half of the fan shroud off and have a good look down between the radiator and air conditioning condenser, probably a pile of dirt and debris built up.

Looking from the outside will not tell you anything and blowing water or air from the outside will not clean it out either.

When the air flow through the AC and rad is restricted so is the flow of air through the transmission cooler.

A 98 did not come with a transmission temp gauge so I am guessing either someone installed an aftermarket one or you are reading the temp with a scan tool.

For it to cool down all that metal and oil from 300 to 220 in 10 minutes to me sounds questionable, this could suggest the sending unit or gauge is not providing an accurate reading but my money would still be bet on a build up between the rad and condenser.
 
If you are not the original owner, check to see if the tranny fluid lines are still connected into the engine rad.

And that the original rad has not been replaced with one meant for a 350 vs 454.
I know they sell two row and three row rads. There are likely four row versions out there also.
 
I assume you were towing with the trans locked in 3rd gear and not OD. If you were towing in OD it's a wonder the trans survived like it did.

When I was with Ford, we had a Crown Vic come in where the owner had been pulling a 28' camper in OD. Some of the aluminum parts in the trans had been so hot they were actually welded together. I couldn't believe it when Ford still covered it under warranty.
 
Sorry to inform you, but that is NOT true!

Let me tell you my take on transmission flushing.

First thing - there are at least 10 different transmission fluids on the market. They are not necessarily compatible. It just isn't good policy to mix fluid types or to use a different fluid than what is recommended by the manufacturer.

Second thing - There is NOTHING short of a complete disassembly and a replacement torque converter that will remove and/or replace 100% of the old oil. Why? Because there are too many places in a transmission for oil to "pool" up and lay. There is no way to effectively flush out a clutch drum or servo completely. Oil goes in and out the same place. Some oil will ALWAYS remain in a servo or clutch drum. Many parts in the transmission rely on splash for lubrication.

Third thing - oil. Transmission flushing amounts to connecting a machine to the transmission cooler lines. Oil is pumped out by the hydraulic system and "replaced" by oil from the flushing machine. The oils will MIX. Assuring a complete exchange of fluids is virtually impossible. There will always be some residual original oil left in the transmission. Even if you pumped a whole 55-gallon drum of it through the transmission.

Last thing - oil compatibility. What kind of oil is being pumped into the transmission being flushed? Is it the CORRECT oil for the unit being flushed? Given that there are many different oils in use today, what is in the machine? Unless the machine is used exclusively on one make of car, I would say that the odds are pretty high that the oil is not correct.

In conclusion, my humble opinion of transmission flushing is that it is a rip-off that can potentially damage your transmission. Claiming 100% oil replacement is simply fraud.
 
Let me offer some explanation about transmission heat.

Where does it come from? Partly from the engine, which operates at around 235 degrees F. The majority of it comes from the oil turbulence in the torque converter. There is very little if any heat generated by the clutches, bands, or planetary gear sets. If the clutches were generating heat, they would burn up or burn out in short order.

Most all transmissions today have a TOT sensor - transmission oil temperature. This sensor tells the computer the temperature of the oil in the pan usually. If the oil starts to get too hot, the computer will lock up the torque converter to reduce heat buildup. This eliminates the heat being built up by the oil turbulence in the torque converter. At least that is how Fords are set up. I'm sure that the other carmakers have similar setups.

Towing in overdrive is generally not a good idea in hilly country or under high load conditions. As was already said, the torque converter will be frequently locking and unlocking resulting in more heat buildup.

Since the transmission is cooled by a coil in the radiator by the same coolant that is cooling the engine, an auxiliary cooler AFTER the cooler in the radiator is always a good idea. It will extend the life of the transmission.

After having been rebuilding transmissions for over 30 years, I never once saw clutch linings come unbounded. I have seen plenty of them burned out or showing signs of overheating and slipping, but never saw the linings come unbounded. Same with bands. I have even seen torque converters turned blue from overheating or slipping.
 
I would imagine a lot of trannys have been burned up by not having a big enough radiator. If you're going to pull heavy loads very much you need to get the biggest one you can find. A good radiator is a lot less than a tranny rebuild. I had a 94 GMC 4x4 that started overheating and when I removed the shroud there was about a 2" core in there. I said well, no wonder, it has a wannabe radiator. On top of that I noticed the newer engines are a lot hotter under the hood when you lift the hood. I never have any problems with my 72 Chevy 4 core copper radiator and they aren't very much smaller than the radiator in a C50 medium duty truck radiator. I know I've blown a lot of radiators out with air and I always get lots of dust. I like clutch fans because they aren't as noisy. A good flex fan will pull a lot of air but they're a little noisy. A heat gun will always tell you where the heat is. If you do install a flex fan you have to make sure it is in the right position in the shroud or it will actually blow air out the front.
 
(quoted from post at 04:52:51 08/09/20) I was using Drive, not Overdrive. Engine was running normal temps, just over 200. I haven't took the grill off to check anything yet, there is a large electric fan behind the grill on the passenger side of the grill, Is that the fan for the transmission cooler? I will check for smell later today. I have a flat rear tractor tire an hour and a half away that I want to go work on before I start on the truck, yes, I have another pickup, I'm not driving this one. Thanks, Chris
use modern view where this post is visible. It look's like a few responders can't see your post for some reason.
 
(quoted from post at 09:31:23 08/10/20)
(quoted from post at 04:52:51 08/09/20) I was using Drive, not Overdrive. Engine was running normal temps, just over 200. I haven't took the grill off to check anything yet, there is a large electric fan behind the grill on the passenger side of the grill, Is that the fan for the transmission cooler? I will check for smell later today. I have a flat rear tractor tire an hour and a half away that I want to go work on before I start on the truck, yes, I have another pickup, I'm not driving this one. Thanks, Chris
use modern view where this post is visible. It look's like a few responders can't see your post for some reason.

More like the few only look at classic. They only read the first post and then respond.
They do not bother to read any replies or replies to replies.
Thus in modern you see a bunch of replies that are virtually repeating what others have posted.
 

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