You guys won't like this....

I wouldn't find it unusual to see 300°F going to the cooler when the torque converter is unlocked and working hard.

 

normal trans temps can be anywhere from 150 to 220 i run my truck empty anywhere from 160 to 180 empty loaded maybe 200 to 220

 

My kids e4od got so hot the other day that it was puking fluid out the top all over the place. It was showing 6 inches high on the dipstick when I checked it and it was not overfilled. He had to drive across the desert with his full of stop leak radiator to come get me with his 93 IDI in 120 degree temps. I can't believe it made it home and is running fine now. His warning light only came on once and he pulled over till it cooled off but that trans really got hot!

 

Having seen the stock cooler, I believe it would be normal. I also don't buy that it is good for the longevity of the transmission.

 

How can it be 6 inches too high and not overfilled? I don't understand.

Even with a larger cooler the torque converter will get to about the same temperature. It's doing the same amount of work, so it will generate the same amount of heat. The larger cooler will cool the fluid better so that the pan temperature is lower. The lower temp going into the converter will lower the output temp, just not a lot.

 

It was boiling over and out the vent at the top. The fluid was foamed up bad. Good thing we had Mobil 1 in it. It was 3 quarts low when he got home and it cooled off. I need to go get him a new radiator.

 

Thermal expansion. He checked it when the fluid was near the boiling point so the ATF was expanded considerably.

 

It has been 23 years since I took thermodynamics, but I'm pretty sure I've got this right.

So long as the cooler isn't reducing the mass flow rate, the temperature rise is proportional to the heat input. Cooler input would lower the output temperature by an equal amount.

I have to try REALLY hard to reach 260°F, the most I've ever seen so I know the bigger cooler is working. I've found the highest temperatures are found when the engine is only at 1/4 throttle or so. High power causes the fan clutch to kick in solid. Lower power high slip makes less heat, but the fan clutch won't kick in so the cooler is much less effective. I've considered adding a pusher fan with a thermostat on the oil line just for the cooler.

 

I note that you didn't touch this one:

Correct me if I'm wrong on this part:

The pump lifts fluid from the pan. The discharge of the pump has a pressure relief to the pan, but this relief is only a safety in case something plugs and should be closed all the time. The pump discharge goes to the hydraulic controls for the clutches and brakes. The pressure is regulated by the PCM using a pressure regulator that releases fluid to the torque converter to regulate the line pressure. The pressure is adjusted as needed based on the gear selected and the torque going through the transmission to ensure no slippage of any of the clutches or brakes. When the transmission isn't shifting, nearly all of the pump discharge will go to the torque converter. The pressure test port is connected to the pump discharge. If a temperature sensor is screwed in here, it will measure the pump discharge temp.

The torque converter is plumbed to the oil cooler. The cooler return line is connected to the lubrication circuit to lubricate the bearings and gears. To regulate lubrication pressure there is a relief valve that dumps oil from the lubrication circuit to the pan. Whatever oil isn't going through the bearings will dump from this relief.

Looking at this thermodynamically, the lowest temperature is in the cooler return line. Fluid going through the bearings and gears will pick up heat cooling those parts. The fluid dropping from the transmission internals will blend with the bypassed fluid in the pan. The pan temperature will be higher because of this warmer fluid from the internals. The fluid then going through the torque converter will be heated significantly going through the torque converter if the converter is unlocked.

For most of the transmission parts we are concerned with the line temperature. Since this is much cooler than the TC outlet temperature when unlocked, we aren't as concerned about the rest of the transmission parts getting too hot.

The flow circulating in the torque converter is orders of magnitude greater than the flow through the cooler so essentially the temperature inside the torque converter is equal to the discharge temperature. We have to concern ourselves with the seals in there, particularly the front seal. There's also a lock clutch up there and it sees the torque converter temperature. Once you've heated the TC up to 300°F getting going, that lock clutch is going to be asked to lock up.

So that goes back to my question, is 300°F in the torque converter good for the transmission? How long will fluid last when 5 of the 17 quarts is sitting at 300°F? How well do the seals hold up to this? What about the lock clutch?

 

You have a lot of it right.

The torque converter is fed by a valve that regulates the pressure to the converter at 120 PSI. It is fed all the time except when the flow demand on the pump exceeds the pump's capacity. Typically this only happens for a very short time during a shift, but if the engine RPM is low and load is high the main pressure regulator (the valve that regulates line pressure) can cut flow to the torque converter to maintain pressure to the internal clutches. The torque converter can operate without pressure for a few seconds. So anytime line pressure is 120 PSI or more the converter is seeing an input pressure of 120 PSI.

The torque converter clutch is capable of locking at 300°F. It often won't because those temperatures are generated in conditions where the stock programming won't allow the converter to lock. If it had been my decision I would have locked the converter in a lot more operating conditions than it does. I didn't work on the 4R100 directly so they didn't ask my opinion.

The converter, clutch, and seals are capable of living with 300°F for no more than 1/2 hour at a time. Longer than that can make parts too soft to seal.

 

Thanks for all the responses.

So how is it regulating the pressure? By adding a inline restriction or dumping the excess to the pan?

What sets the cooler flow rate? Is it only what is used by the lubrication circuit, or does more flow?

At least in the 4R100 the torque converter doesn't unlock as soon as you let up on the throttle. It sure would have been nice to leave it locked during coast for at least a little bit.

I'm usually able to get the TC to lock in first or second when climbing long steep hills by giving it 100% throttle and then letting up once it's locked. If I keep my foot on the throttle just above idle when slowing down to corner I can keep it locked. If I do this then heat isn't a problem.

How about at 260°F.

 

When converter pressure is below 120 PSI the valve opens and bleeds flow from line pressure to the converter. When it reaches 120 PSI the valve closes and stops bleeding pressure from line pressure. It never dumps to the pan.

It is set by converter pressure and restriction in the lube circuit.

It can tolerate 260°F for a bit longer than 300°F. Ford's standard is over 250°F for no more than 1/2 hour at a time.