Transmission Cooler for Auto

[ngatioka]

Welcome Ngatioka,

Did your AT Temp warning light come "ON" when you had the 2nd gear lockout ? No lights came on

Were you in drive or sports mode when the lockout happened ? Yes

If you were in drive did the "D" display flash on and off ? When I flicked back to drive no "D" flashing

If you were in sports mode, were you trying to and select 3rd and the transmission wouldn't change up. Yes

At what speed did this happen ? 50km and what throttle position ? Unsure but same position to keep the speed

ASC selected OFF ? Yes if not was ASC light flashing ?N/A

Was Traction Control light flashing ? Did not see anything flashing on the dashboard at all

[old Jack]

Some thoughts.

Thanks Ngatioka,

Great information, I have done some reading/thinking about this as it seems to be a frequent issue when towing up long hills or on long stretches of soft sand but my current thoughts are;

The 2nd gear lockout is not a temperature related issue unless the AT Temp light is "ON".
The AT ECU has a function to prevent transmission damage under certain high load conditions, ie uphill towing and long stretches of soft sand. In all cases reported on the forum high load and high engine rpm seems to be a common denominator.

According to the Service Manual the protection lockout can occur when the transmission is in "D" or in "2" or "3" or "4" or "5" if using the sports mode.

When it occurs in "D" then the "D" flashes and 3rd gear is locked in and you can only downshift to 2nd by moving to the sports mode or into "N" (the gearbox will not upshift!), both actions effectively drop engine rpm and vehicle speed, after speed and rpm have reduced you can select "D" or "3" and the gearbox resets.

When in sports mode then the ECU limits the transmission to 2nd even though you can select and have displayed "3", "4" or "5" the ECU over rides your request whilst certain unsafe conditions are present and will not change up gears until safe conditions return.

In both the above cases the AT ECU is looking for certain conditions and although I don't have the internal logic of the program I am guessing that the AT ECU will be looking at wheel speed, ASC system, Traction Control system, ATF Temps, Engine RPM, AT output shaft speed and throttle position. Based on any number of conditions or combination of conditions the AT ECU will go into protect mode and lockout the trans. Most likely it will be calculating the amount of slip occurring in the torque convertor and when this is too much it goes into lockout mode. Excessive TC slip will cause damage to internal transmission components and the ATF will overheat and lose its lubricating and hydraulic properties.

Fitting a torque convertor over ride lockout kit, which I am told fixes this and other issues, the torque convertor is manually/electrically locked so no slip occurs to the point were the engine can stall just like a manual transmission. If you had a manual and the driving loads exceeded the engines torque capacity then even at full throttle the engine rpm will drop of rapidly forcing a down shift or an engine stall. I think that with a TC lock kit you may see the same effect as the manual trans and engine rpm will wash off. I do not know if there are any negative effects of the TC lockup kit but I suspect if used often, for large periods of time and in high load conditions the electronic TC lockup components may wear or fail prematurely much the same way as a mechanical disc/plate type clutch will fail if mistreated or overloaded.

It would be interesting to have a manual and an auto Challenger both working hard and see how the manual is performing when the auto goes into lockout mode. Are we expecting to much performance from the auto? Do we need to drive a little easier in high load situations to prevent the AT ECU from intervening.

cheers, old Jack.

[picard]

Fantastic old jack, more info here than you would ever get form mit`bishi service centre

[260DET]

What I have decided to do is to get an engine/transmission temperature monitor, with a thermo fan switching facility, and then wait and see. If the transmission runs too hot then a thermo fan on the transmission cooler radiator will be installed.

[old Jack]

Thermo fan on ATF cooler ????

Richard,
I may have the math wrong but I do not think that fitting a thermo fan to the ATF cooler is going to improve cooling except if you are stationary and then the transmission is not under load.

A read of the Davis Craig thermo fan performance graphs on their website tells me an 20cm thermo fan is capable of 180 litres per second maximum which = 10,800 litres per minute which = 1,080,000 cubic centimetres per min, divide this by 314 square centimetres (the area of a 20 cm dia fan) and this gives you the speed of the airflow through the fan, so the number is 3439 cm per min or 34.39 mt per min or 2040 mt per hour which is only 2.04 kph!

Even if the thermo fan is mounted on the back of the ATF cooler so it is sucking air through the cooler, a 20 cm fan with an area of 314 squ cm mounted on a 20cm x 30cm ATF cooler with an area of 600 squ cm at air speeds of 2kph through only 46% of the coolers area it is unlikely to reduce ATF temperatures. In fact the thermo fan will actually restrict the free airflow through the ATF cooler by 6% based on the area of the fan hub alone and not taking into account the effect that back pressure generated by the fan itself will have on the airflow.

Someone please check my math and reasoning as I did read on the Davis Craig website that thermo fans are ineffective at speeds greater than 50 kph. Have I got it wrong as it is a big difference between 2 kph and 50 kph!

cheers, old Jack.

[captain_paj]

Hi guys,

I don't have a Challenger - from my sig you can see I have a '94 NJ auto.

I just thought I would share my experiences and thoughts.

Firstly - I would NEVER run a vehicle with the in-radiator auto trans heat exchanger still connected. WAY too many vehicles have issues with this, they can crack and when your trans cools down, it can suck water into the trans and then it's dead.

There are MANY factory recalls and technical bulletins all around the world from vehicle manufacturers - and yet they CONTINUE this practice.

And it doesn't just happen to vehicles with high kms either. BA/AU Falcons are a good example, but Toyota, Mazda, and many other shave issued technical bulletins to dealerships re problems in the warranty period.

Secondly - airflow is EVERYTHING for transmission cooling. When I bought my NJ this time last year, when towing a trailer on the highway I would lose overdrive due to heat. My NJ has a Bocar bullbar, and the opeing in said bullbar didn't line up with the cooler - in fact the cooler was receiving NO airflow. I reversed the mounting brackets to drop the cooler down into the airflow from the opening in the bar and from that point I had no problems with losing overdrive.

From the picture that Old Jack put up - looks like your cooler doesn't sit tight up against the radiator. I have found this to be a suboptimal position, and at slow speeds or while 4wding its REALLY bad. I had a dead air con condenser fan and this didn't help - once I replaced this fan, it pulls air through 1/3 of the cooler and this makes a HUGE difference to its cooling efficiency at slow speed.

One of my fellow Gen 2 owners (Barneymutt) has a truly epic cooling system on his Paj. Two big PWR coolers mounted side by side and they successfully keep his transmission cool while towing a caravan up even the worst of hills. But get him offroad and they work not very well. He needs fans.

I personally added a smallish Fluidyne cooler from the US to my Paj - the fluid runs to it (having as I said bypassed the in radiator heat exchanger) then to the factory cooler. But the Fluidyne is butted up against the air con condenser, thereby getting air SUCKED through it from the engine fan.

This kicks butt over Barneymutt's setup offroad. Towing a caravan? I don't know as I don't own one. I reckon he would win hands down. But for my purposes it's GREAT and I'm really pleased.

Would I want to run without the Fluidyne cooler? Nope. Would I want to run without the factory cooler? Again - nope. Without the factory heat exchanger? YUP.

If I had a Challenger, I would personally be bypassing the heat exchanger and mounting a cooler to the radiator/condenser so as to get air sucked through from the engine fan, while keeping the factory cooler intact.

Also - carefully choose the design of your cooler. My Fluidyne cooler (I run the exact same one on my BA Falcon, again with exchanger bypassed) is half the surface area of a PWR or Davies Craig with the same BTU rating. It's substantially thicker than them, but it's the design of the fluid channels and fins that puts it ahead, and it has great airflow though it. I'm not a fan of the tube and fin style - not that you normally see that with PWR or Davies Craig...

Slow and high speed cooling are different things and require different solutions. My thinking is cover BOTH bases. It works REALLY well for me, and this is a guy who was having heaps of problems with overheating trans.

Take my advice with a grain of salt - but I wouldn't bother with a fan on the factory cooler, I would just remove the heat exchanger and put on another aftermarket cooler.

[260DET]

Thanks old Jack and Captain, very useful info. Old Jack, having done a fair bit of cooling problem solving with the race car I'd agree that at higher road speeds a thermo fan can be counter productive, except where the natural airflow to the radiator is poor in the first place.

So if an overheating problem is encountered at highway speeds with the PB my first thought will be to improve the natural airflow to the radiator. I've found that proper aero optimised ducting can make a big difference but it will be some time before I get the time to pull the front off the PB to have a good look. The engine monitor I have ordered has a switching capability so the thermofan option will be there if needed.

[old Jack]

Thanks "captain paj"

Thanks "captain paj" for you input it got the brain thinking and resulted in more research about this topic so in reply to your comments;

"suboptimal position" yes you are correct this cooler is less than ideally located both being some distance from the A/C condenser and being at an angle. The distance issue can not be corrected as the cooler is mounted on 2 brackets that are welded on to the intercooler mounting tube and there is insufficient room behind the mounting tube (amr75wcr has posted a photo on "what did you do to your Challenger today" on the 20/1/13). As air will always take the path of least resistance, the only way to improve the "sucked" airflow from the fully shrouded engine fan is to fill in the gap between the ATF cooler and A/C condenser, this could be done with some rigid silicone or rubber sheet cut to size and then siliconed to the ATF cooler or by using auto grade gap filling foam sheet. Care would need to be taken so no chaffing occurred on either the ATF cooler or A/C condenser.
Although the ATF cooler is 30 cm x 20 cm only half of this area is exposed to ram air even though the cooler is mounted at an angle to increase this ram air exposure. The top and bottom 1/4's are shielded by chassis and body structural members that can not be removed so a vertical plate on both the L/H & R/H sides of the ATF cooler protruding forward that will stop the sideways spill of ram air and then deflect ram air to the upper and lower 1/4's of the cooler would improve airflow through the ATF cooler.

How much improvement from these 2 mods is unknown without accurate in and out ATF temp measurements before and after the mods but it should improve the cooling efficiency of the ATF cooler.

I agree with the bypassing of the "radiator" ATF cooler, it should be possible but will be a awkward job due to limited access, I suspect this mod may have the greatest effect on ATF cooling temps.

Due to lack of space fitting a larger cooler is a major job and may not be possible.

Fitting of an ATF thermo fan, if physically possible, will have little positive and in my view a negative effect.

So Richard I think your latest thoughts on airflow improvements and temp monitoring are worthwhile.

cheers, old Jack.

[old Jack]

Hope this gives you an idea about what and where I am talking about.

cheers, old Jack.

[captain_paj]

Hope this gives you an idea about what and where I am talking about.

cheers, old Jack.

You put up damn good photos Jack!

Man you modern 4WD owners have a busy front area don't you?

It's a pretty darn decent cooler IMHO. It is just suffering due to the tradeoffs placed on it in terms of positioning/airflow.

Is there actually a space between the condensor and the radiator? If there is - man that would be a good spot for a cooler. Then again if there IS - that to me is a BAD BAD BAD design, so maybe it's just the photo that makes it look like that.

Can the cooler just be relocated to the front of the condensor and use a $5.99 mounting kit from Supercreep?

[old Jack]

No Space

Unfortunately there is no space available to relocated existing or put in an additional ATF cooler, if you look at amr75wcr (Wayne) photo on "what did you do to your Challenger today" 20/1/13 you will see how congested the front of the Challenger is.

cheers, old Jack.

[260DET]

That insert you have drawn old Jack should help, as it is there is no reason for air to flow through the transmission radiator, taking the path of least resistence air will tend to flow around it. So anything that directs air towards the cooler is good. There is a bit of space behind the radiator which helps as air exit is just as important as air inlet.

I bought a book on car aerodynamics to help design some stuff for the race car, fascinating subject but nothing fancy required here to make a difference

[TheWall]

So to ask a dumb of question of people who are more mechanically minded than me....does the tranny cooler need an upgrade for a Chally that will be doing some long stints towing in hot weather and/or off road?

[old Jack]

So to ask a dumb of question of people who are more mechanically minded than me....does the tranny cooler need an upgrade for a Chally that will be doing some long stints towing in hot weather and/or off road?

From the work and comments that everyone has contributed I think the answers to your questions are;
1. Factory ATF cooler is ok in size but just badly located, unfortunately relocation or replacement is not easy, only thing is to increase airflow by fitting inlet air deflectors to direct air into ATF cooler and to shroud the rear of the ATF cooler so the fan can suck air through the ATF cooler at low speeds.
If you have a factory front (splash) bash plate then air flow directly onto the ATF cooler can be improved by opening up the area on the left hand side of the bash plate to match the centre and right hand panels.
2. Bypass the ATF cooler in the radiator as this is considered to not be beneficial and possibly detrimental to ATF temps.

Has anyone done these mods yet? they are still on my wish list!

cheers, old Jack.

[PeterC51]

AT cooling in 2016

From the work and comments that everyone has contributed I think the answers to your questions are;
1. Factory ATF cooler is ok in size but just badly located, unfortunately relocation or replacement is not easy, only thing is to increase airflow by fitting inlet air deflectors to direct air into ATF cooler and to shroud the rear of the ATF cooler so the fan can suck air through the ATF cooler at low speeds.
If you have a factory front (splash) bash plate then air flow directly onto the ATF cooler can be improved by opening up the area on the left hand side of the bash plate to match the centre and right hand panels.
2. Bypass the ATF cooler in the radiator as this is considered to not be beneficial and possibly detrimental to ATF temps.

Has anyone done these mods yet? they are still on my wish list!

cheers, old Jack.

I'd love to see this thread revisited to find out what people may have done to improve AT cooling - what works, what doesn't. Anyone care to share?