When is an ATF too hot?

[mechtech2]

175 is best for an auto tranny. Like they say, 160-175 or so.
200 won't kill it, but is approaching concern.
If it only sees 200+ for short times, forget about it.
[trans temps very a lot]

 

[weebl]

Okay, so I have the gauge in and fully functional. Observed it today in truly mixed driving and I must say I'm concerned - not about what towing temps likely will be, but about stop and go city, no trailer in tow.

Not even gridlock, just some downtown driving and city arterial with lights. Temps averaged 190F and peaked at 210F. Looks like a cooler may be in order for a different reason than I anticipated.

Doing an early drain and fill on the latest change for sure!

 

[Trav]

Quote:
Your Ford like my GMC has a tranny fluid cooler in the radiator. Your engine thermostat is most likely 190*F, so that would be the temp of your tranny fluid


What if the cooler is mounted on the bottom of the radiator?
if the coolant is 195 going in the top are you saying it does not get cooler as it goes through the radiator before being returned to the engine?

Try your IR thermometer on the top and bottom and see.

 

[Jim Allen]

weebl: You are still OK! A 190 average is pretty good from the converter line in traffic. 210F isn't terminal and it's short term. That oil is not going to break down very fast at those levels. You gotta remember you are seeing the outflow from the converter. In the pan, it's probably 40 percent cooler. And I'll tell you... you are still likely to see similar temps out of the converter after you've installed a cooler. Not to say a cooler isn't a good idea just that you shouldn't expect magic because you are reading from the hottest and most changeable part of the trans lube circuit. Cooler efficiency (oil to air cooler) also depends on ambient temps and on hot days, you won't get as much action from it. The opposite will happen in winter, and you might overcool (more a danger for short hoppers). In reality, the radiator cooler delivers the most consistent performance in all temps.

 

[weebl]

Originally Posted By: Jim Allen
weebl: You are still OK! A 190 average is pretty good from the converter line in traffic. 210F isn't terminal and it's short term. That oil is not going to break down very fast at those levels. You gotta remember you are seeing the outflow from the converter. In the pan, it's probably 40 percent cooler. And I'll tell you... you are still likely to see similar temps out of the converter after you've installed a cooler. Not to say a cooler isn't a good idea just that you shouldn't expect magic because you are reading from the hottest and most changeable part of the trans lube circuit. Cooler efficiency (oil to air cooler) also depends on ambient temps and on hot days, you won't get as much action from it. The opposite will happen in winter, and you might overcool (more a danger for short hoppers). In reality, the radiator cooler delivers the most consistent performance in all temps.


Okay, that's what I thought, no need to panic yet. And I did pick that spot for the temperature sender as I figured it would be the hottest point and would want to know that as what the worst temperature is in the system. A/C was also running full blast, adding to the strain on the cooling system, and we had one of our rare-this-year hot days (85F ambient).

If I do find after more observation, especially after towing, that temps are staying high too frequently, I guess I will need to figure out what the right level of cooling is. Looking at Derale applications for my vehicle, there's essentially a light duty (recommended for 2,000 lb towing), medium duty (3,500 lb towing, and incidentally the capacity of my vehicle, which I tow close to) and heavy duty cooler (5,000 lb).

 

[Trav]

Quote:
In reality, the radiator cooler delivers the most consistent performance in all temps


+1

Some high quality builders of 4T65E units actually advise against adding an aftermarket cooler. They claim its rare to have a unit fail from fluid issues but rather in most cases its a hard parts failure.
I suspect the same to be true of most other units unless they are in tow service.

Mine runs 172f @ 95f* ambient temp around town with only OEM radiator cooler only.
* 2 bottles of lubeguard red, Dex IV and transgo accumulator kit.

 

[rslifkin]

It's pretty hard to overcool an automatic to the point of hurting it. Some newer trannies don't like running cold though, as the computer will force them into a warm-up mode of sorts, wasting a bunch of fuel. On my Jeep, I'm running a 11x11x3/4" cooler (biggest one sold at AAP) with the rad cooler bypassed. I've driven the Jeep in 2* F weather, and the tranny has warmed up enough to enable OD and TC lockup after about 1/3 of a mile, and shifts/runs fine. I don't have a gauge on it at the moment though, so I don't know how cold it was running.

 

[Jim Allen]

True, it's hard to overcool them in most situations. The exception might be short hoppers where you might never bake out moisture or allow the trans to operate properly due to it's internal sensors never sensing warmup. Remote possibility and applicable only to a select few, of course, but worth keeping in mind.

My trans 4R75E Ford trans needs 85-90F (sensed internally) before it locks up and the cooler is bypassed until about 150F. That's another thing you are starting to see more, OE cooler bypasses.

 

[Trav]

Quote:
4R75E Ford trans needs 85-90F (sensed internally) before it locks up and the cooler is bypassed until about 150F. That's another thing you are starting to see more, OE cooler bypasses.


I can imagine a aftermarket oil cooler working okay in high summer but not in freezing temps unless it has a system like yours or a thermostat in the line.

 

[rslifkin]

^ FWIW, mine doesn't have any sort of cooler bypass thermostat. Then again, the computer only needs the tranny to get to 50* F before it allows full operation.

 

[01rangerxl]

My truck has a 5R44E 5-speed auto with a factory stand-alone trans cooler...the lines do not go through the radiator, the power steering uses that for its cooler.

Typically in the middle winter it maxes out at just over 150* regardless of the type of driving I do.

In the middle of summer, it maxes out at just over 195* in stop and go city driving with lots of lights. Even towing a trailer (approx 2-3000 lbs) on the highway it won't go above 190*. City driving is definitely the hardest on the trans since the cooler doesn't have air flow sitting still.

The highest temp I have ever seen in my truck is 196*. I use a Scangauge to monitor trans temp, and it gets its reading from whatever sender Ford installed at the factory. I don't know where in the trans it gets its reading from.

 

[semaj281]

Originally Posted By: weebl
Originally Posted By: Jim Allen
Be prepared for wildly varying temps and high ones by measuring the cooler out line. That "normal" temp range you found is mostly likely bulk temp... measured in the pan. This is a lower and more temp stable area to measure trans temp than the cooler out line. Measuring the cooler out line, you will see temps climb and fall rapidly according to load and whether or not the converter is locked.

Overall, it's time at temp that counts, so the spikes will you see, maybe 225 or higher, have to be factored by knowing that the pan temp, where the the oil "dwells" the longest, is probably only 180.

I had gauges mounted on the pan, the cooler out line and also the return line back to the trans on one of my past vehicles. At times I saw 100+ degrees different at the cooler out line vs the pan, and where there was a lot of temp differential (cool ambient, hot trans) I saw 90 degree oil going back to a trans with 225 at the cooler out and 185 in the pan.

Currently, I can monitor pan and cooler out of my current Ford and when the converter is locked, the temps run at nearly identical levels. Put the truck to work towing grain wagons, as I recently did during wheat harvest, I saw 240 on the cooler out and 160 in the pan. Within a few minutes of the converter locking, temp dropping 50 degrees

I advise a lot of monitoring before jumping to any cooler or upgrade conclusions.


Thank you. Glad to know I can expect quite a bit of variability as I drive. Wouldn't I want to know what the peaks are? I realize that the pan temperature is more stable, but is knowing that it is spiking up to say 225 not of value in indicating I should consider additional cooling? In towing, I can usually feel and hear when the torque converter has unlocked, at which point, I immediately shift out of D on this 5 speed transmission, and into 4. I understand that this transmission can lock the converter in 3rd, 4th or 5th. A side benefit I see is when my wife is driving while towing, who may not hear or feel the torque converter unlock. She doesn't care to be mechanically inclined, but has driven manual transmissions and uses that frame of reference for shifting to a lower gear manually, rather than understanding that by going into 4, you are doing this to force the transmission from an "unlocked" 5 into a (hopefully) "locked" 4th. I can now hopefully use the gauge to advise her when it climbs above x, shift into 4.



Please explain this further. If the converter is unlocked, does that mean it's slipping? What's the converter doing when I'm cruising at a steady speed in overdrive? And at a standstill, with the car in gear? At WOT?

 

[weebl]

To understand the torque converter, imagine a sealed vessel filled with hydraulic fluid (which is essentially what ATF is). You have a shaft connected to an impeller at one end, which is driven by the engine. There is another shaft and impeller at the other end, linked to the drive wheels. When at idle, or accelerating, particularly at lower speeds, or sometimes at WOT, the two impellers are not physically connected. The engine driven impeller turns the fluid, which in turn drives the other impeller. When cruising speed is reached at a drive gear, or only if a very moderate acceleration is asked of the transmission, the two impellers become mechanically linked, increasing efficiency, and reducing heat generated. At cruising speed, the RPM difference at the point the torque converter unlocks is usually very small, and probably imperceptible to most drivers, 300 RPM or so. But learning to recognize that, and keeping the torque converter out of that unlocked state while cruising (by forcing a lower gear where lockup is still possible), will help to keep temperatures down, and in turn, increase fluid (and ultimately transmission) life.

 

[weebl]

Originally Posted By: semaj281
Please explain this further. If the converter is unlocked, does that mean it's slipping?

You could say that, as there is no mechanical link between the input and output sides of the torque converter.

Originally Posted By: semaj281
What's the converter doing when I'm cruising at a steady speed in overdrive?

The torque converter will be "locked" and the input and output sides linked mechanically.


Originally Posted By: semaj281
And at a standstill, with the car in gear?

Unlocked. This prevents the engine from stalling, much the same way it is impossible for an MT car to be stopped at idle while in gear, as with an MT, while in any gear, the input and output sides of the clutch are physically connected. Normally 1st and 2nd will not have the ability to lock up, and 3rd and beyond will.

Originally Posted By: semaj281
At WOT?

Depends, partly on how the transmission was designed, and partly on speed. Lower gears, typically unlocked. At a high enough speed in a high enough gear, it may well be locked. I don't know how you could tell for sure as a driver though.

A heavier load will typically cause the torque converter to unlock more easily.

If you want more details, you could start here: http://en.wikipedia.org/wiki/Torque_converter