Aux ATF cooler configuration

[Andrew Prince]

I have won an aux OEM ATF cooler on fleabay, which I am going to fit to ensure better cooling on the autobox and hopefully avoid any potential overheating problems.

A couple of questions:
Firstly can anyone with the OEM cooler fitted please take a couple of pics of the mounting (i.e. how/where it's fitted) and post them?
Secondly, do 80s with the aux cooler fitted also have/use the ATF cooler in the rad as most UK spec autos seem to have?
Thirdly, assuming 80s with aux ATF coolers also have the in-rad ATF cooler, how does the plumbing work in OEM configuration - does the hot ATF from the box go through the rad cooler first or the aux (external) cooler first.

And finally an open question that's been debated at some length previously in various threads - what do people think the cooling order should be, rad cooler 1st or aux cooler first?

Cheers,

 

[Chris]

Andrew, in terms of the second part of your question, my thoughts would be...

A. If the new cooler was so efficient, you might end up putting heat back into the cooled ATF as it passes through the rad - unlikely though
B. If you put it through the rad first you get the cooling that Mr T designed, but put more heat into the engine water. Then you go through the aux cooler
C. If you do that, then you probably are not maxing the capability of the new cooler are you.

So if it were me and I really wanted to go wild..

D. I'd fit the cooler on its own circuit. Pull the rad and replace it with a manual one thereby increasing the cooling capacity for the engine too

Well you did ask.

Chris

 

[Andrew Prince]

All fair points, Chris - I'm with you on all of them. My gut feel is to put the aux cooler before the rad cooler, so the cooling duty on the rad is reduced. My view is that the 80 engine is easily cooled by the standard rad, if anything for our temperate clime the 80 diesel rad probably has surplus cooling for the engine. So I am not worried about overloading the rad, nor am I worried about the rad running too hot (assuming cleanish rad in good condition )

What I do know about cooling/heat-exchanging is that the approach temperatures are quite important - obviously the basic cooling duty is a given (surface area for heat transfer to take place). For the majority of heat exchanger design, a minimum approach temperature of 10 deg C is used. The higher the approach temp difference, the greater the heat transfer - so a 10 deg C stream being heated by a 100 deg stream will see rapid heat transfer but this slows down as the two streams' temp difference (approach temp) gets smaller. For practical purposes, to heat/cool one stream with another with a temp diff of less than 10 deg C will require an unfeasibly large exchange area.
So whats the point about my thermodynamics waffle

Well from what I have gathered, the ATF design operating temp is a touch higher than the engine temp (coolant) and Mr T has designed the ATF temp warnings on the auto 80s to sound at 150 deg C and stay on until the ATF has cooled to 120 deg C. This is way higher than the engine temp. The fact that autos can boil the ATF (i.e. hit 150+ deg C) while running through the std in-rad cooler tells us something - the engine coolant cannot cool the ATF fast enough if the autobox is working hard unlocked! We know that the approach temp difference is big, at least 50 deg C (150 deg ATF vs 100 deg coolant for the sake of argument) so the problem is the rad ATF cooler exchange surface area is not big enough. This may well be an intentional design feature by Mr T as he probably doesn't want a hot autobox to cause the rad to boil or worse. (I appreciate that both the autobox and rad can struggle in heavy going in the Sahara in summer - but that is a rather extreme example, so I am ignoring that for now).

Holding that thought, another obvious design feature is that the rad obviously functions as an ATF warmer in cool conditions and/or from start-up. This is where I am unsure but I assume from this that Mr T has a minimum ATF operating temp in mind. Overcooling the ATF probably isn't great for an autobox either - but I don't know this for sure. Maybe it's impossible in practice for the autobox, with slipping clutches and spinning torque converter to remain cool enough to be a problem

So for those still awake and reading, my thinking is that provided I supply ATF at a reasonable temp (let's assume 50-100 deg C) to the rad cooler, then the rad will provide some minor heating or cooling depending on the ATF temp and the ATF should return to the autobox at a pretty constant temp. This is first prize - for sure the autobox would not enjoy the thermal range of 150 deg ATF and internals being hit with returning ATF at 40 deg C - it might be ok for a while but over time, this will hurt. The punch line - I think I will fit the aux cooler before the rad to suck out the heat if the ATF is very hot (remember there will be a big approach temp cos the ATF will be cooled by ambient air - so we can suck out a lot of heat quickly). The ATF then should be cooled to a sensible temp before going through the rad where it will be maintained somewhere close to engine temp (+-10 deg as per our approach temp theory). Hopefully this will keep the autobox at a constant, optimal temp!

Of course my theory would not apply in very hot conditions (i.e. Libya in 55 deg summer heat!), If I ever have cause to encounter those conditions, perhaps I would plumb the aux cooler after the rad to try and ensure the ATF is as cool as possible going into the 'box because chances are that the box is generating heat very quickly so we would want the ATF to return as cool as possible.

Anyway, sorry for the very long-winded spiel I would welcome other thoughts/comments/criticisms, particularly from those with real world experience Theory is great on paper but not always perfect in the field.

 

[Rob]

Well your theory is sound and I would also put the extra heat exchanger before the rad for those very reasons, as the rad will return ATF at the right temp back to the gearbox regardless what the extra heat exchanger is doing under normal (for europe) operating conditions. But there is one more parameter that you have not considered, the specific heat capacity of engine coolant relative to air, I just though id through a spanner in the works.

EDIT: and the mass flow rate of the cooling streams...

 

[Chris]

Yes, I meant to say that too. I just ran out of time, because I was busy working on my new trans-mat beam idea and was just realigning the flux capacitance return waste gate drain valve

It also matters what colour it is by the way. Radiation, convection, reflection and all that.

But I'd agree. New cooler first, normal rad second. Leave enough pipe to be able to trim if it splits. That's what I learned in Wales, that and carry 10 lits of ATF with you Or bring a Gav with you who'll go and find you some on a Sunday.

Chris

 

[Andrew Prince]

Agreed Rob - my assumption there is that the thermostat keeps the engine coolant at a fairly constant temp, so the amount of cooling that the coolant can provide to the ATF is relatively constant. Of course this would vary in practice depending on the ambient air temp and mass flow rate of the air over the rad but I think the variance would be quite small because the 80 rad is oversized for its duty (I believe ). Overheating autoboxes tell us that the ATF can get too hot to be sufficiently cooled by the rad cooler (i.e. the autobox can generate more heat than the cooling duty of the rad cooler can cope with) - hence my basis that it's the entry temp of the ATF into the rad cooler that's important. Better to cool the ATF before the rad in other words.

The air flowing through the aux cooler also flows onto the rad, so if it's warmed significantly by the aux cooler, then the cooling afforded to the rad is reduced... but the mass flowrate of air should be in such excess that the temp rise and resultant effect on rad is insignificant. Although at slow speeds, it might be measurable... Same applies to a/c rad I guess.

I'm sure the guys at MR T applied their considerable expertise and intellect to this question, hence my question as to how the OEM set-up is plumbed. If the aux cooler is after the rad cooler, then I am missing something important or have the bull by the udders somewhere in my hypothesis (quite possible!)

 

[Bat21]

.... I would welcome other thoughts/comments/criticisms, particularly from those with real world experience Theory is great on paper but not always perfect in the field.

Totally agree with your theory Andrew, this is also the way I was going to go, however...... Julian from OverLand Cruisers recommends plumbing it in AFTER the in rad cooler. He says he has had customers who have done it both ways and the ones plumbing it in down stream get the best results... I can't work out why though

 

[Rob]

We would need to find out more about the environmental conditions, road conditions and driver influence of Julian's customers vehicles to make a informed decision on plumbing it in after the rad. Seems logical to plumb it in before the rad

Andrew only kidding about the mass flow rate and specific heat capacity, there's no chance of predicting accurately the implications of heat exchanger placement (in front of rad near condenser/intercooler...), vehicle speed, thermal load etc. but it may explain why it works for some and not for others

 

[Jon Wildsmith]

I would put the aux cooler after the OEM in radiator heat exchanger I think you have your approach temperatures for the in radiator heat exhanger wrong Andrew When the OEM warning light comes on you should be very worried because the temperature will still be rising and oil seals start to fail. I would want to park it at 120c and you will have to be working the box pretty hard to get above 100c. All that has happened when you hit 150c is you have kept going when you should have stopped at 120c because you've already exceeded the cooling capacity available. IMO as your ATF temps get into the danger zone you have little to no heat exchange going on in the bottom of the radiator. If the ATF goes through the aux cooler first the ATF will pick up heat again when it goes through the OEM in radiator heat exchanger.

 

[Andrew Prince]

I think you have your approach temperatures for the in radiator heat exhanger wrong Andrew When the OEM warning light comes on you should be very worried because the temperature will still be rising and oil seals start to fail. I would want to park it at 120c and you will have to be working the box pretty hard to get above 100c. All that has happened when you hit 150c is you have kept going when you should have stopped at 120c because you've already exceeded the cooling capacity available.

I'm with you on the warnings and the danger that it's too late if you wait for the lights, Jon - AFAIK I haven't ever got into the danger zone with mine (never had the ATF warning light come on). My intention here is to avoid overheating - hopefully that way, I don't have to worry about the alarms coming on

IMO as your ATF temps get into the danger zone you have little to no heat exchange going on in the bottom of the radiator.

This is impossible according to the laws of physics and thermodynamics The only time there will be little or no heat exchange is when the approach temps are within 10 Deg C of each other. This will be in the 90-100 Deg C range (otherwise the rad would be overheating) and 100 deg C should be ok for the autobox, I think?
I take your point that when ATF temps get very high, the rad cooler is not able to remove enough heat to control the temp rise in the autobox. At the end of the day, the coolers are there to remove a certain amount of heat from the ATF - once the cooling system cannot control the heat build-up in the ATF, then temps rise. As mentioned in my thesis previously, because of the slowdown in heat transfer when the approach temps are <10 deg C, I would suggest that once the ATF gets to 90ish deg, the temp rise from there is unavoidable (in the OEM rad cooler only set-up) because the rad will only cool the ATF appreciably once the ATF is more than 10 deg C hotter than the coolant. So there's probably a 20 deg window where the ATF temp simply rises unchecked if the gearbox is generating a lot of heat.(Maybe I am saying the same thing here as you were in your quote above ) Obviously ATF flowrate through the coolers is an issue - if the returning flow of cooled ATF is too small a proportion of the overall ATF volume, then the autobox temp will keep rising. My thinking is that with the aux cooler before the rad, a lot of heat is removed and hopefully the ATF goes into the rad cooler at a temp equal or lower than the coolant temp, so minimal heating load is added to the rad. Obviously if the ATF is very different to the rad, then the rad will either heat the ATF (if ATF arrives cooler) or provide some further cooling if the ATF is still too hot - the latter obviously being the critical situation as described.

If the ATF goes through the aux cooler first the ATF will pick up heat again when it goes through the OEM in radiator heat exchanger.

Some questions - do you not think that Toyota designed the ATF cooling system with a minimum ATF return temp in mind? Are you saying that ATF at engine temps (approximately) is too hot?
Having the aux cooler after the rad cooler means that there is no way of regulating the minimum temp of the returning ATF? In gentle driving during winter this could mean the autobox runs cold - I don't know whether this is good for it either? If we know the OEM configuration of an auto 80 with the OEM aux cooler, then we can tell for sure.

Thanks for all the input - please keep it coming

 

[Jon Wildsmith]

One of the problems with a standard A442F is that such a small amount of the fluid is sent through the cooler. I can't quantify that but so long as you have the in radiator heat exchanger in circuit IMO there's no danger of the in box ATF being too cold. When your ATF is at 80c your box is working quite hard, the radiator exchanger is still adding heat so the temp is rising faster than it needs to. At 90c - 110c you're working the box extremely hard, this is the work rate and temp range you're looking to get a grip on the temps, and the in radiator heat exchanger is providing little to no heat exchange. If your aux cooler is first and efficient then some of the gains it makes will be lost when the now cooler ATF goes back through the radiator 'cooler' (I'd think of it more as a heater than a cooler ). I'd agree that at 120c and above the radiator 'cooler' could be removing heat but a) effect on the whole ATF volume is marginal at best and b) you might as well stop, the heat input is way beyond what your coolers can cope with, unless the crest of that dune really isn't too far away

That's just my view on it based on observations of gearbox failure posts / experience and typical ATF temps I see

 

[Andrew Prince]

Thanks again, Jon - your real world inputs are much appreciated! Do you have a feel for what the normal ATF operating temp should be? Does it reach a steady-state temp in normal use?

Do you know if the box is sensitive to low temps? It obviously functions from start-up in winter, so the ATF could be zero or colder and the box tolerates it. I wonder whether there is a danger of long-term damage of running it cool (say 40-50 deg)

Apart from rare (once or twice a month) longish trips, my 80 typically does <5mile trips, so I doubt the box gets up to operating temp that often. I would not want to over-cool it IF this is a potential cause of problems.

Anyone out there with the aux cooler fitted as standard who can confirm the flow/configuration? SimonD?

 

[Dave Docwra]

I was going to fit an extra oil cooler, but decided to go for the less is more option & instead traded up for fully synthetic ATF oil.

 

[Chris]

Purely out of interest, do we know just how the fluid is circulated? We're talking about a smallish amount going through the cooler, but looking at the pipe runs, it could be that it's pretty much the same fluid going round the cooler. When you are using the box, I presume (I don't know, I am presuming) that much of the fluid is tied up in there. Remember that when you come to drain it, you don't get much out even when it's been standing on the drive. The cooled fluid is returned to the pan where maybe it just sits. If you run lowish on fluid does this mean that there is an effect on circulation too where there isn't any flow round the cooler? You will presumably need to add more fluid to replace that which will sit in the cooler and extra piping.

I know that a lot of this is hypothetical but to get the best cooling, you actually need to get the hottest fluid out and round the cooler. When I pulled the TC from my white one, I realised that most of that fluid must spend most of its life in there. Any change looked to be relatively minimal. So does that get cooled by radiation from the housing and if so, can you improve the air flow over the TC.

I'm not up there with you guys on this thermal dynamics stuff, but it strikes me that you could expend a lot of effort cooling a small proportion of the fluid. Will pushing it through the aux cooler actually slow it down too so that in effect LESS fluid goes through the system?

Just thoughts. That's all. Not proven facts.

Chris

 

[Jon Wildsmith]

The fluid is partialy diverted from what's coming out the TC on its way back to the pan so it's the hottest hardest worked fluid around. When the TC is locked there is no flow through the cooling circuit, because there's no flow through the TC. When the TC is unlocked there is a constant flow of ATF through it.

50-55c are typical temps for mine cruising with the TC locked and I see maybe 70-80 on a hot day climbing hills and stuff in the UK. In the pyrenees it peaked at 97 when worked really hard. My 100 has the OEM aux cooler.

 

[Andrew Prince]

50-55c are typical temps for mine cruising with the TC locked and I see maybe 70-80 on a hot day climbing hills and stuff in the UK. In the pyrenees it peaked at 97 when worked really hard. My 100 has the OEM aux cooler.

Did you ever measure the temps on your 80? How comparable do you think these figures here would be to an 80?

I stand to be corrected but on the earlier 100s, wasn't the autobox much the same as the later 80s?

 

[Andy]

I have tried both pre rad & post rad, and in the (very extreme desert) conditions I was testing it in it didnt seem to make the slightest difference!!!

I was getting high atf temps when clawing through soft sand, even with 2 extra coolers fitted, and with a tail wind it was even more of a problem whic goes to show that the extra coolers DID make a difference , as driving into the wind (over the same ground) dropped the temp considerably.
Also to drop the temps I used low box for a while, (ie getting the box to lock up) and even with the higher engine revs the water temp did not rise alarmingly.
But the solution to all of the problems was quite simple really, I fitted a wholesale automatics valve body with manual lock up switch.
Sorted!!!

Having said that you must remember I was driving in extreme conditions (Gilf Kebir & Uwaynat areas), and not on normal roads.
On normal roads in europe my atf temp stays around 60 -65, and rises a bit on uphil slogs.

I have mounted my coolers between the chassis rails under the rad, as you can see in the photo, they are protected by the bash plate (not shown in pic), which also seems to funnel the air under the winch bumper & through them, but to conclude, I didnt notice any difference in temps pre or post rad, and now they are still plumbed after the rad.
BTW my temp guage sesor is connected to the union where it comes out of the auto box, ie in theory the hottest point.

https://picasaweb.google.com/lh/photo/X ... directlink

Andy

 

[Jon Wildsmith]

Did you ever measure the temps on your 80? How comparable do you think these figures here would be to an 80?

I'd say they're very similar but if anything the 100 is worked harder because it can

I stand to be corrected but on the earlier 100s, wasn't the autobox much the same as the later 80s?

IIRC they changed the TPS valve to a PWM driven electronic solenoid but otherwise it's basicly the same but petrol and diesel don't run the same box in the UK, in an 80 or a 100

 

[Jon Wildsmith]

I was getting high atf temps when clawing through soft sand, even with 2 extra coolers fitted, and with a tail wind it was even more of a problem whic goes to show that the extra coolers DID make a difference , as driving into the wind (over the same ground) dropped the temp considerably.

What sort of temps were you seeing Andy?

 

[Julian]

Interesting reading this, for somebody who has the new valve body on his list of to do's and who has had to have his 'box rebuilt once
Jon, is the oem plumbed in before or after the rad one?
Also would it be a candidate from some form of fan on a thermostatic switch like the Xeng one Jon has used for his bonnet scoop