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AT Transmission Heating up



Its a constant battle avoiding the AT oil Temp light coming on while
climbing the dirt roads of Ethiopian highlands.
They are the worst roads I've had the pleasure of so far.
Have tried everything -
Drive as hard as I can - mainting higher speed to increase airflow and
assist radiator cooling. This has had the best results so far but when
it does overheat the coolant is boiling - I mean aggressively bubbling
boiling. I assume the additional heat is generated from racing the
engine. This requires at least a half hour cool down period and the
high temp leads to increased chance of Temp light coming on on the
next incline.
Have also tried driving slowly ( below 1800RPM ) - this dosent work
either but when the light comes on its only a five/ten minute cool
down period and no agressive boiling of coolant.
Its the same whether I'm fully loaded or running light load of fuel
and provisions.
Of course the big variables are rate of climb, outside air temp and
road surface - all impact the frequency of cool down stops.
On the plus side my diary is in good shape after ethiopis:)
Is there anything else that can be done I wonder??? Any suggestions or
experiences appreciated.
AT oil (OEM) and filter was changed 10K km ago. Coolant is topped up and OK
If I was doing this trip again there is no way I'd have AT
transmission and I would advise anyone intending to go off road in
Africa to stay well away from AT transmission. Not only do they
overheat, are not suitable for sand or big altitue variances, but
there is no knowledge base here for service or repair if they did go
wrong. Opposite being the case for manuals.
My AT transmission is ceretainly the worst piece of kit so far.
My ARB rear diff is a close second but will save that for another day
PS - the Hilton in Addis Abba rocks!! They have real food.
You did not mention if overheating occurs with the transmission in
high range or low range as well?
If in high range, that's pretty what is expected to happen after a
long run with the gearbox struggling to keep the wheels turning. If in
low range, then you need to look carefully at the A/T cooling circuit,
and aggressively bubbling A/T coolant is a worrying sign indeed.
Do you have an extra A/T cooler in front of the main radiator?
Roman (London, UK)
'92 HDJ80 (auto)
On Tue, May 13, 2008 at 1:56 PM, Niall __ <[Email address removed]> wrote:
Hi Roman
Only heats up in high range. Have not had any need for LR yet - apart
from Libya - it overheated there too.
The agressive boiling only happened when racing up hill - a
practice/test I've now stopped - and so has the boiling. I'm nearly
sure this additional heat was generated by the engine as opposed to
the AT box......
I have an additional AT cooler (below the main rad) but its very well
protected by a plate of the ARB bumper - which reduces the air flow.
I'm looking for a workshop and am going to cut out a section of the
bumber to increase the airflow - this should help...
I know it feels like you can do most tricky bits in high range but you
do often need the low range to spread the load between the A/T and
transfer box. I had a problem with the red light coming on once or
twice after long runs on soft sand (this or climbing is still same
thing for the engine and drive train). When I got into the habit of
switching to low range before the climb, it never happened again, even
while driving 500 meters up the crater of Waw el Namous on soft
volcanic ash. The engine nearly died but the A/T held pretty well.
I am not sure how your "additional" radiator is fitted. The OEM hot
climate A/T radiator sits on a bracket right in front of the main
radiator and is not obscured at all. If it is hidden somewhere, think
of moving it to a more exposed position, or even fitting a bigger one.
Under normal conditions one part of the drive train should not heat up
another, so I doubt that the heat from the engine could affect the A/T
box (only except through the engine coolant acting on the small oil
radiator underneath the main radiator).
Roman (London, UK)
'92 HDJ80 (auto)
On Tue, May 13, 2008 at 2:24 PM, Niall __ <[Email address removed]> wrote:
Hi Jon
Interesting!!. I was thinking that low range was for pulling boats up slips.
SO the problem looks like its operator error..... Stupid!
What is the max speed you can do in low range - do you know?
Typically between 30 and 60 km/hr - on a very steep gradient
I see the light! Can't believe I didn't think of the Low Range option.
Do you know what speed you should limit Low Range useage to? - Or
other constraints on same?
Its a Kenlowe - location is good - except for airflow issue and
bullbar which i will rectify. Moving it is not an option at the
Agreed. Nor would the AT oil boil the coolant - this has to n=be the
engine - overworking - more operator error.
Thyanks a mill for the input.
I have some more hills tomorrow
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The other option is to run in high range 2 - the transmission is locked up
in this ratio as well I believe. It might get you a bit more speed than low
On 13/5/08 15:07, "Niall __" <[Email address removed]> wrote:
Jeremy Llewellyn-Jones
Mob: +44 7831 458 793
Hi Jeremy
Can anyone second that? (excuse the pun)
On 5/13/08, Jeremy Llewellyn-Jones <[Email address removed]> wrote:
I haven't tried yet Jeremy's technique so can't comment if it is just
as effective. My assumption for using low range was that since the
lower transfer gear ratio works in favour of the A/T gearbox it will
a) lock the torque converter, b) spread the load, hence heat
disspipation, between more gears.
I would not worry too much about climbing at high speed when the
wheels have good traction, only for adding momentum before the climb.
If you take it easy, you will not spend too much time in low range
anyway and switch to high range as soon as possible. That works OK for
steep inclines, but on the other hand a long, sustained run up a low
gradient should not create overheating.
Roman (London, UK)
'92 HDJ80 (auto)
On Tue, May 13, 2008 at 3:07 PM, Niall __ <[Email address removed]> wrote:
The coolant being above boiling point is not too much of a
problem (you do mean the engine coolant?), that's why the system is
under presure - so that the coolant can get over boiling point without
boiling- this is normal. When you stop and take of the rad. cap you
will get bubbles, leave it to de-presurise for a bit.
If your LC is like mine your AT cooler is in the bottom of the
main rad, so cooling of the rad. is the best option.
Run your coolant at 50/50.
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.
Hello Niall,
Date: Tue, 13 May 2008 13:56:47 +0100
From: "Niall __" <[Email address removed]>
I run a HDJ80 with A/T and took it to several overland trips including
Northern Africa where I extensively played in the sand dunes.
Personnaly I never had any heating problem on the A/T nor the engine. But
every time I playing rough (rough for the A/T) it was only 35=B0C outside and
I would stop regularly for taking pictures or waiting for friends.
I understand the constant overheating problem is anoying you but I'm
suprised you don't appreciate the smoothness and reactivity of the A/T in
off-road conditions especially in sand. I just return from Tunisia and had
the chance to drive a friend's truck with M/T in the sand and I really had
the feeling I had to drive hard in order to avoid being stuck...
I've also experience, more than any other times, that tire width make a huge
difference in soft terrain like sand. My friend HDJ80 was fitted with
275/75/16 tires and though it was much more powerfull than mine (preped up
pump, turbo, exhaust, intercooler, ...) the truck was much more fitting
through the sand than mine (basicaly stock) with 235/85/16...
Anyway, back to your problem, here's a few ideas that might help:
- Narrow tires (see above)
- add an electric fan on the front oil to air cooler. By the way, is your
A/T cooling system modified? I've seen some horsepower hungry people remove
or relocate their A/T cooler to install a large intercooler in front of the
radiator... baaad !
- check if the oil-to-air cooler is working. From my understanding, the A/T
is first cooled by the engine coolant by an oil-to-water cooler in the
radiator. Then, when A/T oil temp rises too much, a valve opens up and let
it run through the oil-to-air cooler =3D> is yours getting hot?
- Go synthetic A/T oil. It's expensive but cools better and protects your
tranny when overheating.
Hope this help.
Been there, done that... had an AT overheated, new AT needed! Ouch...
Lock up is above 45 mph in high, so prolonged and real heavy stress is in
low only! In high one has to find a speed higher than 45++ mph and disengage
OD to be resonably sure that the AT has locked up... I dived quite a bit at
the time I had the trouble to find out why, and what I could do about it,
especially avoid it happen again...
The larger the tires and the more heavy the vehicle/load the more likely the
problem is, of course...
An aussie firm makes kit to handle the issue but not tried it myself...
Possibly these links kan provide additional information:
At a recent trip to the Alpes I tried to drive with care for my AT...
meaning I made an amount of traffic block occassionally where I saw the need
for low range... that was at steep inclines with thight turns, as the speed
could by no means be kept up enough to lock in high... once back I had my AT
fluid changed, and it looked very fine, so I beleive it can help... I drive
a 10-person bus version (DK invention, tax initiated) where I have a metal
pin holding the AT cover in the cabin, and when that gets too hot to hold my
finger on, I tend to believe I'm nearing troublesome heat in the AT....
I know: Install a temperature gauge, an electrical vent on the AT cooler etc
etc... but again, troubles seem to be rare on my A343F even so, and every
install could mean other problems.. so far I have kept it there... others
seem to be abusing their vehicles and still not seeing AT troubles, so
perhabs the way it is done is the difference...
Regards... Henrik
Hi Guys
I have been thinking about this issue of Nialls AT heating up and all the
I have a AT aswell and when I enquired about this heating up to the point
that damage would be done I was advised to do two things.
1, change to Synth fluid and only a good one which will not break down too
2 fit as big a cooler as could be fitted.
Now I dont drive hard or in extremes so the issue hopefully will not effect
But why would the AT build up heat to boiling point just by travelling up
steep hills and would a manual not do the same.
If the cruiser is put in Low and the transfere case locks up as it should
then will the AT change up gears or will it remain in a low gear because the
speed will be low.
If this is the case would this not increase heat because of the higher revs.
How do you know what speed to travel at when in low, will the engine be
working harder and be noticeibilly straining or will the cruiser just not
want to travel at speed, like if you were pulling a heavy trailer.
If a CV goes I think I was advised to put it in low and it would get me home
but would this still be the case if travelling up a steep hill with no
john 92HDJ 80 1HDT
If the box is in lock-up it will come out if it thinks fit, the
same as it comes out of overdrive.
Losing a CV puts all of the power on the front axle on the other
one, so you are in with a good chance of breaking it if you are in
rugged terrain.
The speed to travel at in low is an experience thing, the same as
the speed to travel at in first gear.
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.
Roughly speaking, when running in low range on flat ground, the
engine does not work harder, only faster in order to keep up the same
speed. There is no extra strain on the engine in the sense that it has
no more work to do, it just has to rotate more quickly. Diesel
engines, by their own nature, are low revving engines, so
running them for a long time at 4k rpm will cause wear and tear.
Roman (London, UK)
'92 HDJ80 (auto)
| Its a constant battle avoiding the AT oil Temp light coming on while
| climbing the dirt roads of Ethiopian highlands.
As a manual gearbox type I have no experience of this, but I've been
reading this thread with interest!
One thing did occur to me though: it's very low-tech and I'll probably
get laughed at electronically but ...
You know rally cars tend to have a system fitted whereby they can spray
water onto their inter-coolers to get a short-term power boost? What
about the same deal for your hidden-away AT fluid cooler? I was
thinking of something really simple like a hand-pumped spray connected
to a jerry of water, to be used when working hard uphill. Details would
depend on what you've got available, but if you've fitted a shower then
you've got 95% of the bits already.
If you do this then - ideally - you need to spray enough to make it
evaporate, but no more, since the heat required to turn water into
vapour at 100 deg C (the latent heat of vaporisation) is far greater
than that required to heat it from 0 to 100 deg C. So leaving drips on
the road would be wasteful of what must be a precious resource in that
Having done the sums I think this is a valid proposition. The latent
heat of vaporisation of water is 2260 kJ/kg, so each litre of water can
take away 2260kJ of heat. Your engine is probably putting out 100kW
(100kJ per second) when climbing hard, and maybe 10% of this is lost in
the AT box, ie 10kJ/second.
So vaporising a litre of water will remove 226 seconds worth of heat
completely at fullish power. (This ignores the energy required to heat
the water to boiling point, so it will do a bit better than that.)
The AT cooler won't "see" all this heat, so a sensible spray rate is
probably about 1/10 litre per minute at full power. A 5 gallon jerry
can contains 22.5 litres, giving perhaps 3 or 4 hours of cooling by this
OK everyone, you can laugh now, but I think it will work - and at near
zero cost too!
Incidentally manual transmissions can get hot too, but I think mainly
due to heat from a hard-working engine pushing all that hot air down the
transmission tunnel, as I never get any significant heating in cold
weather. However I have noticed that my transfer box gets hot when
towing heavy loads a long distance at speed, and apparently this is
Also a manual box + the torque curve of the turbo engine is a nightmare
in the alps. I found that I sometimes had to get down to 1st for the
steeper and sharper bends, and then I couldn't get enough speed up to
make it into 2nd before the next bend, so progress was slow, but it did
make me realise just how hard an AT box would be working in those
conditions. On the other hand going *down*hill was a breeze, if a bit
noisy: stick it in 2nd and just dab the brakes gently from time to time
as required.
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The spray water system works very well on engine radiators. This
is a mod detailed on the LCOOL website, or used to be.
Clive Marks
Home: +44 1293 514600
Mobile: +44 7821 491897
Crawley, West Sussex, UK.
Hi Guys
Thanks for the replies.
I just had to ask because along with following this tread I changed the
engine oil filter nearly directly after a run and found it was so hot that I
could not hold it at all.
So this got me thinking about the temp of the oil both in Niall's AT box and
my engine.
So does anyone know what temp it takes to boil AT fluid and what temp would
the oil reach normally in the engine if you concider the temp guage was at
normal 1/2 way mark yet I could not hold the filter.
john 92HDJ 80 1HDT
Hello Chris,
On Thu, May 15, 2008 at 10:08 AM, Christopher Bell
<[Email address removed]> wrote:
I think under certain circumstances it might work, though I myself
would not want to depend on it. Niall seems to be rather unlucky as
such overheating problem is uncommon.
As far as the maths is concerned, during the Saharan hot season 22
litres of water will sustain one person for max. 5 days, which equals
0.0030 litres per minute. Compared to 0.1 litre per minute at full
power to gain 3 or 4 hours of cooling, I'd rather make frequent stops
to enjoy a glass of water.
Roman (London, UK)
'92 HDJ80 (auto)
Fair comment, and I wouldn't want to depend on it either - but he wanted
a solution, and I think this is a practical one.
Total loss evaporative cooling systems are not unheard of: just before
WWII Supermarine produced a Spitfire cooled this way for an attempt on
the world air speed record, the aim being to eliminate the radiator and
its associated drag. They never completed the job since they were
"rudely interrupted" by events in Poland ...
And, as you have indirectly pointed out, the human body also uses the
same method to dump excess heat!
| As far as the maths is concerned, during the Saharan hot season 22
| litres of water will sustain one person for max. 5 days, which equals
| 0.0030 litres per minute. Compared to 0.1 litre per minute at full
| power to gain 3 or 4 hours of cooling, I'd rather make frequent stops
| to enjoy a glass of water.
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