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does ATF cooler increase or decrease engine cooling efficiency?


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19 replies to this topic

#1 grossgary

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Posted 22 May 2013 - 10:44 PM

2002 H6 automatic VDC. 

i can envision two possibilities of adding an ATF cooler:

 

1.  ATF cooler pre-heats the air and reduces radiator cooling efficiency - increasing radiator/engine temps.

or

2.  ATF cooler removes work from radiator and increases efficiency

 

which is it....or is it a wash and there's no change?

 

this question is important because i'm towing large loads and exceeding maximum engine cooling capacity/ability (engine temps too high). this is common with this vehicle, the cooling capacity is the weakest link when towing large loads.


Edited by grossgary, 22 May 2013 - 10:51 PM.


#2 Fairtax4me

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Posted 22 May 2013 - 11:42 PM

I don't see it making much of a difference from an engine cooling standpoint, though keeping the engine heat out of the ATF by bypassing the heat exchanger in the radiator will help prolong ATF life. The biggest factor in ATF lifespan is temperature, overheating ATF by just 10 degrees cuts about 10,000 miles off the service life of the fluid. Overheating by 30 degrees basically destroys ATF, its protective properties just go out the window.

You might think about adding a temp switch for the fans so they turn on earlier. You could also put some Water Wetter additive in the coolant to improve its heat transfer capability.

#3 presslab

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Posted 23 May 2013 - 12:08 AM

The first law of thermodynamics states that energy is not created or destroyed, it just changes form. So all things being equal either scenario would be a wash because the energy needing to be dissipated is the same. But they won't really be equal exactly. For example, running an external trans cooler will allow the body of the trans to be cooler. So in this case less heat will be dissipated by the trans and more in the cooler, actually slightly increasing heat up front.

For towing, I'd certainly say an external trans cooler is needed. Really any Subaru automatic should have an external trans cooler to get the best life. You could mount it somewhere not in front of the radiator, like in front of the front tire. Maybe get creative and cut some exhaust vents in the splash shield. I personally hook it up as follows: trans outlet->external filter->external cooler->radiator cooler->trans inlet. A separate trans cooler thermostat is not a bad idea either but I find my setup keeps the trans cool enough (and warm enough in the winter too).

#4 NorthWet

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Posted 23 May 2013 - 01:18 AM

I don't think that this is a simple question to answer.  Although presslab has a point regarding thermodynamics, it does not take into account imperfect thermal transfers to the cooling media (air).  More heat energy is transferred to ambient air by a hot body than from a cooler body.  I'd have to think this through properly, but my gut says that placing the ATF cooler near the hot side of the radiator (inlet from engine) would have the least negative effect on cooling capacity.

 

Ideally, though, it would be better to have a separate cooling air stream for the ATF cooler.  SVX folks often put theirs in the space between tire and bumper.



#5 grossgary

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Posted 23 May 2013 - 07:46 AM

having it out of the flow of the radiator would be ideal, i just didn't know how much air flow it needed itself.  temp gauge will be in order.



#6 Numbchux

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Posted 23 May 2013 - 08:55 AM

The trans cooler is built into the radiator (as it should be to work correctly). The transmission operates at a higher temperature than the engine, but it only needs a relatively small capacity cooler and low volume through it because it's letting the coolant do most of the work. In order to do the same job, but only relying on airflow to cool the fluid, a much larger capacity cooler would be required. The correct way to add an external trans cooler, is to add it in line AFTER the cooler in the radiator. This way the ATF gets cooled off considerably as it goes through the radiator, and then is cooled off further in the aux cooler.

 

 

So the answer is simple. The heat energy generated by the transmission is put directly into the engine coolant. Of course, the rest of the cooling system is built to accomodate that, so it's not really a big deal.

 

 

 

As presslab said, energy cannot be created or destroyed. The engine converts the energy in the fuel to heat and torque. An Automatic transmission takes the torque from the engine, and in order to function, some of that torque is lost and converted into heat as well, which has to be dissipated.

 

A Manual transmission is much more efficient, so much less of the torque is lost and converted into heat.


Edited by Numbchux, 23 May 2013 - 08:57 AM.


#7 presslab

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Posted 23 May 2013 - 10:04 AM

The correct way to add an external trans cooler, is to add it in line AFTER the cooler in the radiator. This way the ATF gets cooled off considerably as it goes through the radiator, and then is cooled off further in the aux cooler.

I tried it like this at first, as everyone said it's the "correct" way to do it. Even in the moderate California climate the transmission was over-cooled. If the temperature was near freezing the trans would take a while to get into 4th gear, and forget about the torque converter ever locking up. These features are in the TCU to improve the warm up of the transmission; it's a good thing to warm up the trans fluid, it improves the fuel economy/emissions and the wear in the transaxle.

I the wintertime with the external trans cooler BEFORE the radiator cooler, the radiator will be able to warm up the transmission fluid after being over-cooled. In the summertime it's not a problem either; the external cooler will do the bulk of the cooling and the radiator cooler will still shed some heat if it's above the coolant temperature. I don't see any downside.

#8 bulwnkl

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Posted 23 May 2013 - 12:15 PM

Exactly. Most users need the factory heat exchanger to help warm the ATF much more of the time than to cool it. Plumb the factory cooler in 'last.'

#9 johnceggleston

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Posted 23 May 2013 - 09:52 PM

unless the air temp is close to boiling, both the ATF cooler and the rad are going to help cool.

 

plus the trans is designed to operate with the ATF at or near the coolant temp.

 

if you could hang the ATF cooler down low like a fmic, that might help.

 

or use a sawzall to add a hood scope and mount it above the engine.



#10 grossgary

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Posted 29 May 2013 - 08:31 AM

u

 

or use a sawzall to add a hood scope and mount it above the engine.

LOL

 

 The heat energy generated by the transmission is put directly into the engine coolant. Of course, the rest of the cooling system is built to accomodate that, so it's not really a big deal.

 

so if ***engine temps are too high*** then removing this heat generated by the transmission will reduce engine temps?   i'm really only asking about towing huge loads over mountains. how to mitigate that properly.  i understand the basic system and how it's supposed to operate - but what to do in this specific situation (besides drive my truck LOL).

 

it's fine to about 85 degrees....at 85 or more i need to do something.

 

ideally you have a thermostat for the ATF right - keeping the temperatures proper at low load and high load....but i can't do that.  a better radiator doesn't seem practically available.....



#11 MilesFox

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Posted 29 May 2013 - 09:37 AM

I would run it from the output line thru the trans cooler before the return to the radiator and back to the trans. 

 

There would  be the question to mount the cooler in front of or behind the radiator. 

 

My ford van had a factory unit which was mounted at the top of the radiator in the front near the driver side corner of the radiator.



#12 ivans imports

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Posted 29 May 2013 - 09:42 AM

make shure you chage the inline fillter is hiden in the ds fender well and gets overlooked on this car was a remote fillter this will cause more problems than a oil cooler will. Why they did this I dont konw But I never see them changed. The six had problems eating up planetarys I dont think a cooler will help with that but it may.



#13 Gloyale

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Posted 29 May 2013 - 10:47 AM

make shure you chage the inline fillter is hiden in the ds fender well and gets overlooked on this car was a remote fillter this will cause more problems than a oil cooler will. Why they did this I dont konw But I never see them changed. The six had problems eating up planetarys I dont think a cooler will help with that but it may.

 

The H6 exhaust runs right under the drivers side of the trans pan.  The spin on filter that is used on 4cyl. models would come too close to the exhaust.  You can install the spin on type into the h6 trans by unbolting the blockoff plate, and installing the threaded pipe (kinda like adding the engine oil exchanger to an EJ)

 

If oyu do this, then the filter lives very close to the exhaust pipe.  On ours, I cut the exhaust, and added a curved piece to take it out away from the filter a few inches, then installed a heat sheild around the filter.



#14 NorthWet

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Posted 29 May 2013 - 05:07 PM

An additional thought:  If you need periodic, acute cooling (pulling up grades as contrasted to flat cruising), you might want to consider an "open" heat sink.  Run a length of metallic (preferably copper) tubing through a volume of unpressurized water.  This will have minimal effect below the boiling point of the water (other than to slow down tranny warm-up), but will sink tremendous quantities of heat as the water vaporizes.  The vented, total-loss system keeps things simple, water is cheap, and you are no worse off when the water is all vaporized than if you didn't have it at all.  Varying the amount of immersed tubing and/or allowing the total loss coolant to run at a slight pressure would allow some control over ATF temp.



#15 ivans imports

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Posted 30 May 2013 - 09:39 AM

aluminum ribed trans pan more fliud cappacity racers do thiss to dissapate heat



#16 bulwnkl

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Posted 30 May 2013 - 06:52 PM

it's fine to about 85 degrees....at 85 or more i need to do something.


I had very nearly this exact circumstance with my turbo Baja. Putting in an external ATF cooler and bypassing the factory ATF heat exchanger entire had zero impact on the problem. My translation/conclusion: ATF temps, at least on turbo Bajas, are not significant with respect to overall radiator load. What I had to do was change to nearly-straight water to get things under control. I added Water Wetter, and ~15% glycol to prevent the heater core freezing due to the A/C, but only the change to a lot more water in the cooling system helped.

Good luck!

#17 nipper

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Posted 30 May 2013 - 08:39 PM

It is neither as the heat load vs the air flow is very small. An AC coil can add much more heat if the radiator is on it's way out.

 

Depending where you live, you have to look at it more as a heat exchanger then a cooler. The radiator assits on heating the fluid in winter, so I always mount them before the radiator. I run a temp gauge so in winter the difference is notable.



#18 grossgary

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Posted 01 June 2013 - 12:02 AM

I had very nearly this exact circumstance with my turbo Baja. Putting in an external ATF cooler and bypassing the factory ATF heat exchanger entire had zero impact on the problem. My translation/conclusion: ATF temps, at least on turbo Bajas, are not significant with respect to overall radiator load. What I had to do was change to nearly-straight water to get things under control. I added Water Wetter, and ~15% glycol to prevent the heater core freezing due to the A/C, but only the change to a lot more water in the cooling system helped.

Good luck!

 

great thanks BulW - more water really helped, excellent.  this gets straight to my real issue, i need to dump more heat no doubt, the car tows great, but the cooling system isn't up to the task.  there are no H6 aftermarket aluminum radiators though...so i'm limited.



#19 Numbchux

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Posted 01 June 2013 - 12:41 PM

I'm sorry, I misunderstood. I didn't realize you were asking about adding a trans cooler to reduce your engine temps.

 

 

No, I highly doubt that would work. You need to focus on the engine cooling.

 

4 things you can look into.

1. Increasing your coolant-cooling capacity. i.e. larger radiator. I know that's not an easy solution, but adding some sort of cooler inline with the heater core lines might be an option (grab a junkyard heater core and plumb it in with a manual water valve....)

 

2. Increasing the efficiency of your coolant. i.e. changing the antifreeze mix. Of course, use caution, increasing the percentage of water in your system will increase the cooling efficiency, but will also increase the freezing point. IMO this is not an option in MN....

 

3. Oil cooler. Not much more to say there....I know ones with a thermostat in them exist. Add a little extra cooling capacity to the other fluid in the engine.

 

4. Increase the airflow. Car engine bays are almost always a high air pressure zone. Lots of air going in, not much coming out. There are hundreds of ways to do this....Everything from spacing the hinges up and removing the rear hood seal to allow air out the back, to cutting/drilling holes in the hood, legit hood cowls, scoops mounted backwards, new vents, junkyard vents etc. etc.

 

here's a thread with some ideas:

http://forums.nasioc...d.php?t=1977436

 

I know a friend of mine added a WRC-style vent right behind his radiator, and it drastically lowered ambient temps in his entire engine bay, lowered average coolant temperatures, and intake temperatures (he had a front-mount IC as well). I'm not sure where he got it, but similar to the real thing seen here:

subaru_impreza_ii_wrc_01-copy.thumbnail.



#20 NorthWet

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Posted 01 June 2013 - 01:48 PM

Regarding the ATF's temperature on engine coolant temperature, under "normal" situations it should be negligible.  BUT... GG is not talking about "normal" conditions, but rather heavy load conditions.  The tranny itself produces very little heat in steady-state conditions (it will produce a little more during shifting due to the sliding of friction materials); most of the heat comes from the TC when it converts torque.  If the lock-up clutch is engaged, no conversion takes place, things run cool.  When the LU clutch is disengaged, the TC turbines have a speed differential, causing them to shear the ATF, generating heat.  I would expect that heavy towing causes the TCU to unlock the clutch.  As the ATF heats up, it allows an increase in turbine speed differential, which heats things up more...

 

Regarding venting the underhood area:  Any vent should be well forward of the windshield/cowl intake, as this is a very high pressure zone.  (At least one US "musclecar" had a rearward-pointed intake hood scoop to take advantage of this pressure.)

 

Regarding auxiliary engine coolers:  IF you had the room, I hear that the VW radiators (little half-sized things) work really well. If some room but not much, the heater-core idea is good.  If no room, increasing the thermal transfer rate can be done by spraying a water mist onto the radiator core when needed. (Big bang for the buck.)






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