Automatic Transmission Fluid Temperature Gauge

Contact:
Greg Whittaker at
All Trans at Currumbin on the Gold Coast in QLD
he will set you strainght on all of your questions.

I don't have the number handy but you will get it through Telstra.

A Toyota salesman told me you should not so I would check.

I have read a thread on the manual Parado and not to tow in 5th gear, so I would check.

I hope this helps.

It might be worth making enquiries at a place that has specific knowledge about the transmission in the Prado as being an electronically controlled trans it will already have a temp sender in it.
Have a look in the owners manual and see if it has a temp warning light for the transmission somewhere on the dash or auto selector.
If so then an electronics guru can probably tap into the wire and connect a temp gauge to it which should give you a specific temp readout.
Alternatively you can fit a generic gauge and sender to the trans, although it might be hard if the trans doesn't have a drain plug as this is where the sender is usually fitted aftermarket.

Hello Glenn

It is unlikely that towing in 5th will cause heat problems if the torque converter is locked, same with 4th if it also locks. Towing in 5th may cause other stresses but it should kick down before that became an issue. I have a temp gauge on my auto A440 and the temp tends to drop once the converter is locked. Temp gauge a good investment if you are towing as you can stop if heat becomes a problem and let the transmission cool.

Cheers,
Dave

Here is some guidance I posted on another forum in the last 12 months that may be of assistance.
Quote:

The durability of automatic transmissions operating under heavy loads or in duty cycles at the limit of their design capability has always been a challenge for drivers to accept there are some things that must be done to provide a trouble free life.
The problem is that there is not much in the way of published guidelines on what to look for and how to respond to the warning signs.
For those who may be interested I may be able to provide some guidance here that you could find useful.
Looking at operating temperatures, there are a couple of things here.
A stable bulk oil running temperature is a must. If the temperature rises on uphill or generally hilly running or in headwinds then the transmission oil cooling system needs to be boosted.
Bulk oil temperatures less than 110 to 120 celsius should be targeted. (You should see about 90 celsius in your duty cycle. )
Above 120 celsius, there is a real impact on oil oxidation [degradation due to heat] and above 140 celsius there is a doubling of the rate of oxidation for every 10 degree rise in temperature. So the message here is get the oil temperature stable and keep it below 120 degrees.
Now looking at mineral oil based transmission fluids versus synthetics. We’ll use the Castrol products as an example. The mineral oil GM Dexron brand is TQ Dexron 3, and the synthetic product suitable for the Dexron specification is TRANSMAX Z. Some of you have chosen to use Castrol Transynd, similar comments as for TRANSMAX Z apply.
We’ve already talked about bulk oil temperatures, however looking inside the transmission at some of the working areas there are some much higher temperatures generated.
In the clutch pack, the friction plates that make up the clutch are designed to operate within a defined temperature range, usually between 300 and 400 degrees. These clutches are oil flooded and the transmission fluid is used to dissipate the heat generated and therefore control the temperature of the clutch operation, so the transmission fluid has to withstand temperatures much higher than you see in the transmission sump. Elsewhere in the transmission the oil is undergoing much higher temperatures for example in the planetary gear set as gear teeth contact one another [momentary 600 celsius] , and in the torque converter.
It is in these conditions that the mineral oil versus synthetic fluids performance must be compared.
Firstly the effect of heat on the base fluid. The temperature at which mineral oil begins to oxidise is about 140 C, while synthetic fluids of the type used to formulate TRANSMAX Z don’t begin to oxidise until well into the 200’s. So the synthetic is more stable until much higher temperatures are reached.
Next, the rate of the oxidation or degradation is much slower in synthetics, but antioxidants can be added to both mineral oils and synthetics to slow the rate down and thereby prolong the fluids life. Suffice to say the synthetic has a head start here.

Looking at the effect of heat on the viscosity of these transmission fluids shows very little difference between them, they both have similar Viscosity Indexes. They therefore both perform very efficiently as hydraulic fluids.
However the effect of pressure on the fluids shows a different picture. Under the extreme pressures encountered during gear tooth contact the synthetic has a higher viscosity than the mineral oil. The synthetic has a higher pressure-viscosity coefficient. What this means is the synthetics viscosity rises much faster under the high pressure of approaching metal contact this providing a thicker cushion of lubricating oil. It is this property that gives rise to the claim that the synthetics run cooler than mineral oil. They are simply able to keep the metal parts separated for longer thus reducing the time for friction induced heat build-up. With the appropriately calibrated temperature gauge you can see up to 10 degrees difference in transmission bulk oil temperatures. This is the result of the gear set being some 50 degrees cooler in operation on the synthetic.

So considering these differences, there is a real incentive to use synthetic transmission fluids as they are significantly more durable than mineral oils and in turn impart better durability to the transmission.
So to the question of oil drain interval.
My view is this….If the manufacturers recommendation is 40,000 km under normal service and you load up the vehicle for long distances by towing a load nearing its GCM, then you must halve the drain interval to ensure transmission durability.
If you use products like TRANSMAX Z, and maintain the cooling regime as described you will see a return to the normal oil drain service interval and still retain transmission durability.
If you want to extend the drain interval, I recommend you have the transmission fluid tested every 20,000 km using an oil analysis system. These can be purchased from Castrol in kits that have the sample sent to an Analytical Laboratory with the results returned within the week advising on the condition of the oil and its suitability for further service.
If you don’t want to have the oil analysis done think about the cost of synthetics and drain interval in this way.
Let us assume the synthetic oil and transmission service costs $800. You travel 30,000 km each year and have the service carried out each year. It would take 10 years of servicing before you reached the cost of properly rebuilding a failed transmission.
After 10 years [and 300,000km] you could take the transmission out and replace it with a new one, of course you might also just get a new truck too!!!

As to gauges.
The Autometer range is very good and would be available through Auto Transmission service centres or locally at P&A suppliers.

Cheers

Hi Sacred Cow

For the same reason, we took our Patrol to our Nissan dealership to have a gauge fitted, but they didn't do it because it already had a 'warning light' fitted. Not ideal, because they only come on after the oil temp is high enough to have already done damage. Even if you Prado has something similar, still look into getting a gauge so you can see exactly what is happening. We will do so for the F250, even though our caravan isn't heavy for a vehicle of this size. We also fitted turbo EG temp and boost gauges on the Patrol.

I am adamant that overdrive (and 5th in manual) are not towing gears, however on flat or gentle downward inclines, it may do no harm. You will be able to better assess this when you have your gauge fitted regarding oil temp, although temperature is not everything. Lots of people on the forums report that they always tow in overdrive and haven't done in their gearbox (YET - I add). When we inadvertently left overdrive on with the Patrol, the boost gauge went crazy, so there is a lot more involved with towing in overdrive.

Bushtrek,
very informative posting.

Question:- the late model Toyoto Prado D4D 5 speed auto.
Toyota suggest that you do not change the auto trans fluid in the life of the vehicle unless you do a lot of EXTREMELY heavy work.
(have not checked as to what transmission fluid they use, but is something special??)
They also make the comment to leave it in 5th gear or overdrive when towing unless it is continually down shifting.
They also have a over temp trans warning light.
Your comments please, Bushtrak?

Cheers ,
Fazz

hi,we have an 80 series manual and tow a 17ft 6 jayco,i tow in 4th or 5th depending on weather and road conditions(hills etc).I fitted a oil temp guage very easily and when towing it very rarely goes far past the start of the green,i think that temp is 50c.I purchased all the parts from i think autobarn or a place like that which included guage,guage housing,wire,and sender unit which screws into drain plug in gearbox .

EGT is a better indication for towing stress ..
get a tranny oilcooler and there should be no problem when
you watch EGT ... even if your tranny oil stays cool, lugging in low revs will show higher EGT and you should force downshift.

good luck
gmd

Some Transmission Temperature Display kits suggest drilling a hole in the sump to install the sensor - this is a major job that increases the chance of catastrophic oil loss.

If you have a transmission cooler, it's much easier to find which pipe from the Transmission is the outlet, so bind the sensor to that pipe by wrapping copper wire around both. Then cover in multiple layers of tape, to avoid cooling when water spalshes on it.

Thanks everyone for your excellent responses and advice.

Regards
Glenn