AT oil overheating light / gear motor

[lkenya1983]

Hi. We have a diesel VX LC HDJ101 and every time we have gone long distance with heavy loaded the AT oil light comes on when going uphills.
What is most likely the cause of this?
A. The radiator is not genuine toyota.
B. The centre diff lock button was on for a long distance by mistake because the dash light was not working.
C. The gear transfer motor is broken.

Thanks for any feedback.

 

[MikeJak]

burnt atf is the most likely culprit and would cause the transmission to slip and heat up too much. when was it last serviced? I'd say drain, drop the pan, change the filter and refill with fresh fluid to assess. Not sure at what temperatures the AT oil light comes on on the 100 series but usually when they come on the ATF is pretty much burnt out of specs.
in general is always good to add an external atf cooler piggy backed to the rad cooler. many aftermarket rads have very poor atf coolers, just a tube with no fins so they are not efficient at keeping the ATF temp in check.

 

[lkenya1983]

Thanks for your reply. The gear box has been serviced and new filter. After the last trip the transfer motor is blown.
So you reckon option A is the cause?

 

[MikeJak]

I don't think so, the rad may not help cooling as much as it should but what creates heat is transmission slip, does it feel responsive when accellerating or does it feel like it's slipping a bit?
I'd refresh teh fluid, burnt fluid heats up faster and slips.
is the fluid level correct?
transfer motor do you mean the actuator for the transfer box? not sure how that can be related but I don't know the 100series system well. I'd probably take it for a good look by a reputable transmission shop

 

[uHu]

Depends on year/month of manufacture, and market made for. EVERYONE should have this info in the signature line, e.g. model code and month/year.

The early ones didn't have a good, separate ATF cooler. The later ones had a better one. All depend on the main radiator to balance the ATF temp, either heating it up on a cold winter's day, or, most of the time, bring it down to under 100 C. The separate cooler only takes the over-temperature off a bit when under high load. So, if you radiator is a model without ATF cooling at the bottom, you might need a bigger ATF cooler, or another radiator. I suppose both will work just fine.
Re, ATF level, there are several ways to not check the level on the auto gearbox, depending on model/version/year.

 

[MikeJak]

Depends on year/month of manufacture, and market made for. EVERYONE should have this info in the signature line, e.g. model code and month/year.

The early ones didn't have a good, separate ATF cooler. The later ones had a better one. All depend on the main radiator to balance the ATF temp, either heating it up on a cold winter's day, or, most of the time, bring it down to under 100 C. The separate cooler only takes the over-temperature off a bit when under high load. So, if you radiator is a model without ATF cooling at the bottom, you might need a bigger ATF cooler, or another radiator. I suppose both will work just fine.
Re, ATF level, there are several ways to not check the level on the auto gearbox, depending on model/version/year.

Good post, just wanted to add that 100C is still too hot for ATF, ideally it should live at 80C max. That’s why external coolers are really important as a rad cooler will keep the atf at 88 or so art running temps

 

[uHu]

The design of the ATF cooling on the 100 is so that the atf goes through the bottom chamber of the radiator last, before entering the A/T, so whatever temperature the bottom of the main radiator has, that's what the atf will be at. Normally, that will be a good deal under the top radiator temp, if the radiator (& fan & pump) works as designed.
For cold weather driving, this is one of the two methods for bringing the atf up to temperature asap, the other one being that the converter will not lock up until the temp is up to 60 C iirc, thereby helping to put some heat into it.