KZJ78 Automatic and Torque Converter

[MikePrado]

Hi guys,
I am currently living in Africa and have a 1994 KZJ78 Landcruiser Prado with a 1KZ-TE engine and an Automatic Transmission.

I recently went up a nice steep hill (tarmac) and by the time I had reached the top I noticed that the A/T Oil Temperature light had come on. My hypothesis is that the gearbox which was left in DRIVE (D) was overheating due to the torque converter.

Soon I want to tackle the Ngorogoro Crater (next to Serengeti in Tanzania) which has a 45 minute climb and is apparently mega steep (about 800 vertical meters).

Can anyone please confirm how I make sure that this Torque Converter is locked and so we will not overheat the gearbox. I have read on this post on Offroad Express that if we engage LOW (L) gear then the torque converter should be locked.

Also, to descend, should engage LOW (L) to lock the gear box and maybe low-ratio so I can use the engine to control our speed?

Thanks guys.

Cheers,
Mike

[oldblue]

With your model Auto you can only lock the Auto in 1st, any other gear has pretty well no hold back. I tow a caravan and use the auto as if it was a manual box. Take your time and use the gears.

[kbushnz]

The light that came on is an temperature warning...
I would suggest that since you are in Africa and the ambient temperature is high during the day that extra cooling is required for the auto...Typical for vehicles that tow a lot also.
Also you might want to check the state of the fluid and if its at the correct levels....

So an oil cooler should be fitted, as big as you can fit.

As for torque converter lock..... The auto is ecu controlled and the torque converter is set to lock in 3rd or OD and in my observations above 70 - 80 kph.
Its not designed to lock at low speeds and high load demands as the friction linings are not very wide and can / will fail...(some people operate it manually with a switch)
It will not lock when in LOW....the ecu will still follow its basic rules.

Also do your hard load off roading in low range....
And steep hill descents in low 1st.... will offer some engine braking but not as much as a manual , probably equivalent to 2nd low in a manual.

For more info on the auto search A340E in google....plenty out there...

[MikePrado]

Hi guys,
Thanks for the responses but the information you have given me is conflicting regarding the lockup.

The gearbox from what I have seen on Wikipedia is an A343F.

The real problem is that I don't have time to fit an oil cooler yet I am supposed to do this drive in about a fortnight. I can check the oil level but the car has had less than 7,000km since the auto oil/filter change.

A change of question:
If I need to get up this hill what should I do to prevent the auto overheating?

At this stage maybe I have one answer: leave the car at the top and take a tour 4x4 into the crater and back up (they have serious LandCrusiers).

This is my first 4x4 and I must say that it is completely underwhelming. The 1KZ-TE is the wrong engine for Africa (without intercooler) as I have just replaced the cylinder head due to four cracks. This gearbox can't even carry the car's own weight up a hill without overheating (this is my first auto too and that is a mistake I won't make again). I am just waiting for the next thing to break.

Thanks,
Mike

[tweake]

if you have cracked a head then i would be pulling the radiator tanks off and give it a clean out. while your at it remove any factory transmission cooler and fit an external cooler.
failure to do that will probably mean another cracked head.

[MikePrado]

Hi tweake,

When we did the new cylinder head we also flushed the radiator. We have also had to lock the viscous fan which is not ideal but it is better than trying to find a new one in Africa (if you go to Toyota to get a real one you are looking at at least double Aus/NZ prices). We are also using genuine Toyota Red coolant.

I would have thought that these cars were built for offroading and the stock cooling system should be able to take these sorts of hills.

If I had bought one of these new in Australia it would have been nice to launch a class action against Toyota based on the fact that these cars are not 'fit for purpose' as a 4x4.

Cheers,
Mike

[tweake]

you can't lock the fan without putting a bolt through them which is not recommended as you will end up breaking the fan. but they are easy enough to refill and tweak the thermostat so it comes on earlier.

i don't know that model but i'm well used to the surf which runs the same engine and its also prone to over heating.
you need to take the tanks off to flush them properly.

"not fit for purpose" describes most 4x4's made in the last 20 years

[oldblue]

Just flushing the Radiator sometimes is not good enough, I found my Rad needed the tank removed and the cores roded to remove any scale.
When towing my Van up steep hills I use 1st gear.2000>3000 Rpm

[kbushnz]

Hi guys,
The gearbox from what I have seen on Wikipedia is an A343F.
Mike

The A343F is an A340E with the part time transfer-case....They changed numbers depending on transfer-case options...

I believe you have an underlying problem.
I thrash mine all day lugging 35 inch tyres and the auto is fine....
Albeit not at ambient temps you would get.
Cooling is something worth looking at as suggested already.

I would post your issues to www.ih8mud.com in the 70 series section... They have a few international members and some from africa....

Best of luck sorting it out.

[MikePrado]

Thank you all very much for your help and comments.

Now I will ask for your opinions.

FACTS:
1. The automatic transmission overheat light has only come on once up a very steep hill with the auto in DRIVE (D).
2. I took the car to a pretty dodgy mechanic who thinks I may be about 1 litre down in transmission oil (he was not what I would treat as reliable).
3. I have had consistent problems with the radiator cracking and leaking which I think is due to metal fatigue. It possibly could be a bit blocked both inside the engine cooling segment and the automatic transmission segments.
4. This 1KZ-TE is a very emotional engine and is known to crack cylinder heads if the cooling system is sub optimal.

OPTION
I have found a new, genuine Toyota radiator in Arusha, Tanzania which is correct for my KZJ78. It is model 16400-67030.

With this radiator (and proper Toyota Red coolant) I should be able to:
- be sure the radiator will stop leaking thus protecting the 1KZ-TE's cylinder head.
- be sure the auto transmission fluid is circulating properly and has maximum cooling efficiency.

At the same time I will top up the auto transmission oil to make sure it is at 100%.

It is going to cost a lot of money but from your experiences will this solve the problem? Doing a job like a transmission fluid cooler is not easy here where most cars are fixed with sticky-tape and string (maybe slightly exaggerated).

Secondly, if I take a big hill and keep the car in L (LOW) then will that reduce the heat that the gearbox needs to dissipate through the radiator? Can you please give a dummies explanation on why this would work.

Thanks,
Mike

[MikePrado]

Hi.

One more symptom that I missed:

A few times lately the gearbox has been late changing into overdrive at speed (80km/h plus). Maybe this is a symptom of low oil or maybe the whole gearbox is crapping up?

Cheers
Mike

[kbushnz]

The issues with your radiator could well solve some of your problems....
But I will concentrate on the auto.....

Fluid level is checked by running the vehicle to its at operating temps...
Park on a flat surface and while it is running with auto in P or N you then check the dip stick. Top up thru dip stick hole as required.
If you check it with no engine running the fluid drains back into the pan and you get a false full reading.... As when you start running the level drops...
Can drop as much as 2 liters...

The OD is electronically controlled and has some rules when it will activate.
One is speed, also trans temp and also engine water temp (from memory)
So if it doesn't activate at all then there are a few things that need checking...
Also the electrical solenoid in the auto can get sticky and or fail.....

Now getting to the auto cooling.
Fluid is passed thru a tube in the bottom tank of the radiator.
This does two things... when the auto fluid is cold it heats it to the same temp as the water... If its too hot it transfers the heat to the radiator...

If your radiator is blocked, damaged, etc etc as you suggest then it could be working real hard to try and not only cool your engine but also your trans....

What I have done is put a trans cooler into that line.
Its put in such away to cool the trans fluid first then into the radiator to either heat it back to normal or take more heat out if really hot....

If you are getting very high ambient temps then adding a cooler but bypassing past the radiator could be worth while....
However it may take longer for the auto fluid to warm up and not go into OD and torque lock....

Now for steep hills....I dont know the terrain you are driving ....
If its tarmac smooth etc etc just dropping down a gear will assist.... You may need to reduce speed and just plod up....not sure what speed you are trying to achieve....

Off road hill work....Low range...less stress on the drive train and engine....
But naturally will be slower... like 40 kph...

Its difficult to imagine without being there....

Some reading for you
http://www.autoshop101.com/
Go to technical articles... heaps in there about the methodology of Toyota's including the auto's....and how they operate....

[MikePrado]

Thanks Calvin. This information is really helpful.

I didn't realise that the radiator is both heating and cooling the transmission fluid but it makes sense when you think how the thermostat on the engine works to pass coolant to the radiator only after the engine reaches a determined heat.

I wonder that if the transmission segment of the radiator is slightly blocked which would cause it to heat up more slowly (due to less fluid passing through the radiator) and therefore not going into O/D as easily. It has always worked once we have driven a while so I guess it must be one of the temperature conditions has not been met.

The same blockage would also reduce the amount of heat which is able to be removed from the fluid.

Thanks for that autoshop101. I have some good reading to do but what an excellent resource.

They have a saying in Tanzania 'pole-pole' which means slowly, gently, etc. and is apparently the Kilimanjaro motto. I guess it applies to these Toyotas too

Cheers,
Mike

[tweake]

theres two problems with the transmission cooler in the bottom tank setup.
on some models the cooler restricts the flow out of the radiator and that the heat from the transmission heats the water back up just before it goes back into the engine. so your trying to cool the engine with hot water.

while maintaining gearbox temp is important i doubt you will ever have problems of it being to cold.
if you can fit a thermostat to the transmission line. that will bypass the cooler when its to cold.

[MikePrado]

Hi tweake,
Is there a way to identify which model radiator has the issue and which doesn't?

It looks like we will replace the radiator here with the OEM Toyota one so it would be good to see if we can spot the issue before paying ~$1100 for it.

Cheers,
Mike

[tweake]

sorry i don't know much on those.
the old trick with the surfs was to use the radiator for the manual version which dosen't have the trans cooler.

[MikePrado]

Hi guys,
Yesterday I pulled out the old radiator (which may have been the original) and replaced with a new genuine Toyota one.

We found two cracks the old one on the bottom water pipe to the engine and one crack on one of the auto transmission fluid connectors.

We also checked the transmission fluid level when hot (and engine running) and found it to be down about 1.5 litres. After replacing that amount the gearbox is changing much quicker and the car feels much better.

Questions:
1. How much fluid is in the gearbox when full? I want to know how much impact 1.5 litres would be and whether this would cause the overheat light to show.

2. Will mixing different brands of transmission fluid cause a problem? I couldn't contact my original mechanic so couldn't find out which fluid he used.

Either way I am happy to find the cracks in the radiator as I can now see why we have been losing so much fluid. Hopefully the truck works without problems now.

Cheers,
Mike

[kbushnz]

Hi guys,
Questions:
1. How much fluid is in the gearbox when full? I want to know how much impact 1.5 litres would be and whether this would cause the overheat light to show.

2. Will mixing different brands of transmission fluid cause a problem? I couldn't contact my original mechanic so couldn't find out which fluid he used.

The whole system in mine holds in excess of 10 litres. More closer to 15..
The pan holds about 3.5 to 4 litres...
The rest is in the box and plumbing and torque converter...

So 1.5 litres might have an impact. Also you check it while the engine is running, at operating temp....and in N or park....

As for mixing brands... I try not too but realistically they should be compatible.... Even the synthetic stuff says its compatible with std ATF fluid...

[MikePrado]

Thanks Kalvin.

It is interesting that 1.5 litres makes such a noticeable improvement in gear change speed.

Maybe the cracks in the radiator meant the fluid was not circulating the cooling system properly resulting in overheating.

Cheers,
Mike

[MikePrado]

Hi guys,
Managed to replace the radiator and top up the fluid.

Result:
No problem driving out of Ngorongoro Crater (in fact it was pretty simple) and the radiator is much more efficient at cooling. Used gears up and nice low-range engine braking down.

It was funny as I asked a few of the tour company drivers who had not even heard of engine braking and from the smoke coming from one of their front brakes you could see the result.

Now the next problem... the road between Ngorongoro and Serengeti is so bad that I broke three bolts holding my manual locking hubs. Fun and games.

Thanks everyone for your help.

Cheers,
Mike