Trans Temperatures

ncsutj

ncsutj

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Joined
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Concord
I was towing about 5000lbs with my '13 Silverado 1500 for the first time this past weekend and was keeping an eye on the trans temp gauge. What is a good rule of thumb for trans temps getting to hot? Owners manual says a light will come on when it is getting hot and needs to cool but it didn't say at what temp it would come on. I saw it get up to 170 on the trip from Chapel Hill to Hickory. Truck has 6L80 trans with towing package which includes trans cooler. Has factory trans fluid in it. Not sure if that is synthetic or not. Is 200 hot or 220 to hot?
 
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200 is hot, but not damage something hot. Fluid is good to over 250 but bad juju starts to happen to components at that kind of temps.
I would strive to keep it under 180 with a big enough cooler while towing.
 
With my 6.0 4l80 Trans would run 175 on flat ground and 210-250 in the hills. At the worst hills it would run 260 and same as engine temp.

On my 8.1 and 4l80, it runs 120-150 on flat ground and 175 on the hills. Never been above 200.
 
It depends where the sensor is. It could say 175 and actually be seeing temps 20 degrees more in other places...so keep that in mind. I would stay below 200 if possible. If she gets hotter than you feel comfortable and you had to make the pull...change the fluid asap. Fluid breaks down after a curtain temp is reached and becomes compromised which will lead to other failures down the road
 
My 2010 6.0 hit 200 once or twice but only on exceedingly hot summer days pulling up hills near max GCWR. My 2014 5.3 touched 217 pulling in September up Old Fort Mountain on I-40 near max GCWR. Generally it stays below 200.
 
Here is an interesting chart:
http://myautomatictransmission.com/temperature-chart.htm

Now that said, it really depends on where in the cycle the temp probe is. Immediately after exiting the torque converter it will be t its highest point. I know on my old th350 the difference between output and input was as much 50 degrees even with a minimal cooler.

Be interested to hear what Lee @transman731 has to say on the subject.
 
200 is a good number, i would say that 10 deg above engine temp is too hot. once it's above engine temp the rate at which it starts to gain heat is very fast. with todays synthetic fluids it takes higher temps to create thermal breakdown in the fluid, but there is a fine line between fluid breakdown and plastic melting (there is plastic in 99% of transmissions).
the best place for the temp sensor is in the pan (sump section of the trans) or in the return line as close to the trans as possible for a true temp reading. most of today's transmissions have the temp sensor built into the wiring harness or a sensor in the pan.
 
That is a good chart and rule of thumb. ATF can take a lot of heat and abuse but once you have tortured it, needs to be changed ASAP. Even if you peak the temp out once, you have significantly ruined the life and properties of the fluid. Not worth the risk for a few bucks in oil.

I'm no transmission expert but did teach trans repair for a few years. If you peaked the fluid out to 250 degrees, remember what you are doing to all the plastic solenoids, internal wiring, bushings, etc. as well as the fluid. Your best strategy would be to slow down and work it less or pull over for a proper cool down period. I don't know much about the newer 6 speeds but as with pretty much every trans that was built in the last decade and has more than 4 forward gears, it probably has "lifetime" fluid which is junk and needs to be serviced for these types of scenarios and they are extrememly picky to fluid level so if you do service it, make sure you or the tech knows what they are doing. Temperature is critical these days, long gone are the old dinosaurs that will run on anything forever.
 
This is interesting and although it's certainly not a tow pig, my wife's vw transmission's cooler is tied in with the engine coolant so the Temps run pretty high all the time. I wonder if it would be worth it to run a separate tranny cooler?
 
The 6.0l 4l80 that always ran warm and it remember 6 occasions where both the Trans and engine were at ~250 degrees. The Trans was never usually more than 10-15 degrees above the engine temp. This stock Trans lasted until 220k Miles or so when Lee rebuilt it. We changed the fluid once a year, sometimes less. When it was rebuilt it started shifting very fast and hard with very little load or throttle. It began doing this after extended time on the highway. That when Lee said it was time to fix it. Fwiw to guys wondering how long it will last and what the warning signs are when it stops working as it should but still works somewhat.
 
The trans is tied to the engine coolant because typically they should be the same or damn near close. I would avoid seperating them out since the engine actually helps bring the trans up to temp faster on occasion, keeps it from running cool (which creates shift issues), and removes excess heat. If you are going to add a cooler, most of the time it is better to add the aux cooler before the loop in the radiator. Avoid a seperate trans cooler unless you are getting one with a thermostat and have a temp gauge.
 
I'm probably in the minority and Lee can certainly correct me, but Im not a big fan of servicing transmissions unless you do it religiously from day 1.
Ive seen several used vehicles purchased and the owner tried to do the right thing and changed the fluid and in short order the trans was junk. My old trans guy explained it to me that over time gunk and buildup accumulates in the fluid ports. Then a change to fresh ATF with all the good detergents breaks these accumulations down and they invariably end up hung somewhere they shouldnt which leads to catstrophic failure. His recomendation was to change the fluid and filter every 30k miles from day 1 or just save the fluid money to pay for the inevitable 250k mile rebuild.
 
I think the key word there is detergents. I've had good luck doing trans flushes on really high mileage stuff and also with black tar varnish. I also skipped the cleaner and additive package the kit came with because you are right...down right murder if you run detergents through something that been abused. I doubt putting new fluid in will hurt it. Granted the fluid should be normal OEM style and not 'high mileage' or 'high performance'.
 
Skinny said:
I think the key word there is detergents. I've had good luck doing trans flushes on really high mileage stuff and also with black tar varnish. I also skipped the cleaner and additive package the kit came with because you are right...down right murder if you run detergents through something that been abused. I doubt putting new fluid in will hurt it. Granted the fluid should be normal OEM style and not 'high mileage' or 'high performance'.
Click to expand...

Your standard ATF is full of "detergents" to break down particles.
 
I think if you are at that point, the trans is pretty much a grenade with the pin out and the handle taped. I'm sure there are plenty of stories out there of old rigs that ran forever on tar and sawdust in the pan. Modern day stuff (4 speed and electronically controlled) simply won't deal with that for too long. If it's reached that point and clean fluid pushed it over the top...you just saved yourself a tow or walk home.

A flush is 100 times better than a drain and fill because you are getting new fluid in the converter. If you aren't using the flush preclean and additive package afterwards, you really aren't going to do anymore damage than a simple drain and fill. I'm simply going off of experience using flush machines on new and old cars for years. I've never had one leave or come back broken even after flushing some black fluid out of it. Even if it did, what would say that the contaminant build up wasn't going to do something a week down the road anyway. I can't argue with a guy that build transmissions for a living, I would think his opinion carries some weight with it.
 
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