Cooling Automatic transmissions.

[OP800]

I have searched this subject and only found charts of temp vs life with little supporting information.
Working with my own changes, I now have a system that lowers the fluid temp below pan temp as measured with an infared heat gun.
The temp is measured in the output line from the trans to the cooler and presume it is the converter fluid shear temp at the hottest point.
The coolers are in series and drop the fluid temp below the steel pan temp by about 20 degrees. This seem the possible cooling limit has been exceeded without doing other changes.
Now I have a deep cast alum pan and see the output temp ave seems to be lower (without takeing measurements0 until towing loads are applied.
I have found no information or hardware to do a Pan circulation only system in addition to the present cooling in an effort to try to lower the pan temp further.
I am considering building a 12 volt pump system with cooling radiator to be able to switch on when needed and take temp measurements for collection of data under actual towing conditions.
It's all an attempt to lengthen trans life from heat effects and use synthetic fluid with higher breakdown temp limits.
Any comments on this effort? Has it been done before?

 

[Tmoose]

The few infrared thermometers I have used have been very sensitive to surface finish and material

 

[OP800]

I do know this. It's hard to be sure what you see for a reading is accurate. I try to reflect off a dull or dark surface.
Painting the measurement areas flat blank should give a relitive standard for compairison even if not fully accurate.
A mechanical gage will be installed in the pan then this should make readings more meaningful.
Thanks.

 

[evelrod]

From a racecar point of view, I can address the issue of temp variation with an infrared vs. conventional tire pyrometer...about ten to fifteen degrees with no discernably repeatable pattern...ie...I still use my old needle pyro for my tire temps. This is, obviously, only one exception. The infrared tool is, no doubt, great for other applications.

Rod

 

[Fabrico]

The only true and useful temperature test points are converter output before any coolers, or the sump (oil pan). Which one depends on usage. Many heavy trucks and race vehicles monitor output temp. Cars and trucks for everyday use monitor pan temp. Any tests should be under load.

A torque converter generates anywhere from 80 to 95 percent of the heat in an automatic transmission. Converter output is never less than pan temp. Whatever your coolers are doing will show up in the difference between the two. Temperature after the coolers but before the pan is not relavent information.

Water/oil and air/oil coolers are often run in series, but like coolers should always be in parallel.

Temperature vs. life is a sliding scale. It's what you do for the upper end of the scale that will make the biggest difference.

 

[Rob45]

What's wrong with using a thermocouple?
Put one on your transmission dipstick.
Worry if it goes over 275 F, stop and examine things if it goes over 300 F.

 

[KiwiME]

Well, I guess the point is that the the oil is damaged by being exposed to the highest temperature, which is the TC output - going to the cooler. The pan temp is an intermediate value - not terribly useful and delayed in response.

I had a temp gauge on the "hot" line on my Nissan SUV and found that going up a hill in top gear at about 70mph, the moment the TC unlocked the temp rose by 1 deg F per second. Starting at around 190F, clearly it gets into dangerous territory in little over a minute. It surprises me there is no automatic function to drop it down to third where the TC is happy to lock up again.

I also don't understand how the original poster finds pan temps much higher than the cooler output. Perhaps slightly, but there should be little heat addition from the tranny mechanicals. However, a pan cooling circuit must be a straight-forward mod if required.

 

[Fabrico]

Along with the suggestion that much heat comes from the mechanicals, is that the T/C does some cooling. Neither one is correct.

There is about a 30-40*F average difference between T/C output and pan temperature. A reading of 270*F pan will be around 300*F T/C output. Pan temp of 300 is too much, however, 300 T/C output is not uncommon in certain situations and is not too damaging for a scant few minutes at a time. Time is just as important as temperature.

Another thing people like to do is chase the variations. These are perfectly natural and cannot be stopped unless you replace the T/C with a clutch.

 

[OP800]

I had been having login problems, sorry for the delay.
Some more info.
This trans is a 4r70w Ford in an F150.
Towing close to 11,000 gross combined weight.
The electric gage shows 260f+ at the output of the converter
on the longest hills last summer with a stock steel pan.
I run synthetic blend Mercon V fluid.
Just put a 4" deep alum. pan on.
With normal running and no towing loads yet the pan temp has not gone above 100f as the (new) pan gage starts at 100.
The converter temps are running 125 to 150 so the difference and low loads seem not to heat the pan very much yet. Hope it is a good sign.
Again the cooling loop is two coolers in series 'not' going tthru the engine radiator but stand alone. One is fan cooled by the engine. One is road speed cooled.
We will see in about 2 weeks when we begin to tow to the race track and will give feedback on the results if my login dosn't fail.

 

[OP800]

I had been having login problems, sorry for the delay.
Some more info.
This trans is a 4r70w Ford in an F150.
Towing close to 11,000 gross combined weight.
The electric gage shows 260f+ at the output of the converter
on the longest hills last summer with a stock steel pan.
I run synthetic blend Mercon V fluid.
Just put a 4" deep alum. pan on.
With normal running and no towing loads yet the pan temp has not gone above 100f as the (new) pan gage starts at 100.
The converter temps are running 125 to 150 so the difference and low loads seem not to heat the pan very much yet. Hope it is a good sign.
Again the cooling loop is two coolers in series 'not' going tthru the engine radiator but stand alone. One is fan cooled by the engine. One is road speed cooled.
We will see in about 2 weeks when we begin to tow to the race track and will give feedback on the results if my login dosn't fail.
I could not submit the post several times so be patient.

 

[PLeon]

I have a question, what is the fluid flow through the coolers? With so much heat produced from the T/C during towing, I am wondering if the fluid flow is enough to keep pan temperature low.

 

[OP800]

You raise a good question on flow rate.
These are some of the unknowns unless factory data exists or it is measured.
The lines are 5/16" factory size.
I have found some writings that say not to allow to much pressure drop in the loop because the return fluid is used to lube and cool bearing areas before dropping back into the pan.
I would assume this is where some heat is picked back up again.
The news now is there is pending failure with a lot of metal shaving on the pan magnets.
The fluid was just changed with the last fluid not run all that long. No smell and clear as new fluid.
Finally got a check engine light and a code set for the transmission of P1746 which is a electronic pressure control electrically shorted.
I am inclined to believe this lack of fluid pressure control has really caused the pending failure and not heat deteriortion of the fluid, although the extra heat may have done the EPC control in and killed the trans by proxy.
I just, very recently, put a deep pan on and saw the drop in average temp so I still don't think it was due to oveall operating temp.
Well it's time to either replace the trans with a performance build or another standard rebuild.
I bought the truck with 33,000 miles on before the towing began.
I tried to save it with extra cooling but guess it was already too late. I still will go ahead and add a cooling fan to the second cooler and may still do pan circulation cooling.
For the record the converter output temps ran a high of about 260 during peak loads on hills only then dropped back.
The pan temps have been averaging about 150 to 175 under the same conditions.
With syn blend fluid I would think the heat limits of breakdown are not being approched that much.
So much for back yard engineering trying to make a marginal transmission live under hi loads.

 

[drwebb]

The Mercon ATF spec includes a foam requirement run at 150 C (302 F) suggesting that is not an unrealistic T to experience in service- so you're prolly right that excess heat is not the root problem.

 

[shanba]

The oil going through the cooler not provides bearing lube, but also lube to all the clutches. In addition to the TC, the clutches also heat up the oil tremedously during shifts, especially heavy throttle while towing. Reducing the oil flow through the coolers will hurt the flow available for the clutch cooling and will create higher tempertures during shifts. While shift events are short, the time it takes to cool down after the shift will impact fluid life locally and over time cause the oil to degrade.

 

[Fabrico]

It is highly unlikely that you will pioneer anything in this area, nor do you need to. There have always been two things one must do to make an automatic transmission hold up under harsh conditions. The first is good cooling and the second is firming up the shifts. Neither one by itself is enough.

Have you done anything to make shifting better?

 

[Fabrico]

It is highly unlikely that you will pioneer anything in this area, nor do you need to. There have always been two things one must do to make an automatic transmission hold up under harsh conditions. The first is good cooling and the second is firming up the shifts. Neither one by itself is enough.

Have you done anything to make shifting better?

 

[OP800]

You all have good points.
I do not know what all the return fluid services coming back into the transmission so there should be attention paid to how the total cooling loop is configured to best advantage.
I did know it is best to reprogram the shifting.
With the truck under a warrenty, I was limited as to what I could do without being called on these changes.
At this moment the trans is working perfect but there is a great deal of metal on the magnet in large pieces so I feel failure is around the corner sometime soon.
Dealer will not act unless there is a road test failure and a code set as a normal basis for action.
I am makeing a call on a performance trans co. in N.J. for consultation on a HD build replacement.
We often don't do theses things the best until backed into a corner and and have to act.
Thanks to everyone for your inputs.

 

[OP800]

Latest update is the converter ballooned under heavy loading and took out the torrington flat roller bearing.
This is the metal in the pan and the reason the trans works fine until the next heavy load is put on it. Cooling played little part in the failure.
The performance rebuild will be done with all different clutches, band, hi flow pump, reperogramed valve body and a different converter plus other upgrades items.

 

[OP800]

Update:
Lost the trans not to heat but to a balooned converter.
Heat was never an issue, what a suprise!
What was done:
Had the trans custom rebuilt to heavy duty towing specifications because the stock OEM parts were not up to the heavy application of gross combined weight.
All the major areas were addressesd with a Diesel application lower stall converter, hi flow fluid pump, hi load torrington bearing, bushings, one way sprag, Rabesto PTS clutch packs, re programmed valve body etc.
What a differece in performance and way lower temps right out of the converter.
The shop that did the job has quite a high profile in the performance world. They knew what to do.