School o'clock - Auto Transmission Oil Cooling via Radiator?

[Sam]

Once I know this, this will become a daft question - but because I don't know the answer yet, it's not ... to me at least. I suppose I can have a look and see - but in order to save a potential mess, I'm ready to be schooled if anyone wants to laugh and point while bringing me up to speed?

I've changed radiators before in cars and bikes - but never in an auto. It's only just dawned on me that there's something I need to consider. AT oil cooling.

It's likely that coolant runs around/through the AT box to cool the oil like it does the rest of the engine. Buuuuut, it's not daft to assume that maybe there is a separate compartment in the raditaor that the AT oil is pumped through to be cooled by the air instead. Or both.

Which is it?

Once I've dropped the coolant, when I disconnect the oil cooler inlet and outlet hoses from the radiator, should I expect to see a couple of pink drips of coolant - or a stream of red AT oil? The Toyota manual makes no mention of drainig the oil out of the gear box - or flapping to hold the pipes upright etc - but that doesn't mean I'm not missing something. Feels like it's got to be coolant - but could easily be oil. Coolant or oil?

 

[MODVRS]

The transmission fluid circulates through a small cooler in the bottom of the radiator. You'll get a dribble of ATF when you take the feed and return pipes off but nothing should gush out, just replace what's lost if it amounts to much. There are many threads on here about a well known issue of the engine coolant getting into the ATF and destroying the gearbox, search for "strawberry milkshake". Many folks change the radiator as a precaution to prevent cross-contamination when the rad is getting on a bit.

 

[Sam]

Exactly what I needed - thank you. I appreciate you taking the time

 

[Lorin]

The transmission fluid circulates through a small cooler in the bottom of the radiator. You'll get a dribble of ATF when you take the feed and return pipes off but nothing should gush out, just replace what's lost if it amounts to much. There are many threads on here about a well known issue of the engine coolant getting into the ATF and destroying the gearbox, search for "strawberry milkshake". Many folks change the radiator as a precaution to prevent cross-contamination when the rad is getting on a bit.

No, this isn’t true at all. There are not ‘many’ threads on this or any other forum about a ‘well known issue’ of ATF and coolant mixing because it isn't well known at all. Although it can happen it is actually very rare.

 

[Sam]

Mine's 21 years old and the fins are literally turning to dust. I could probably make a hole by blowing on it hard. In itself that's probably not a reason to panic but I feel like I'm pushing my luck at bit now. Shame they're put of production at Toyota - not sure where to go now. Probably a 3 row something or other from RoughTrax or Milner's - unless someone throws up a red flag

 

[Lorin]

Shame they're put of production at Toyota - not sure where to go now. Probably a 3 row something or other from RoughTrax or Milner's - unless someone throws up a red flag

Genuine radiators can be ordered from any Toyota dealer in the U.K. They are still in production and available. I got a quote for one this week to replace mine. Just be sitting down when you get the price.

 

[uHu]

Just to give another perspective:
ATF cooling is done a few different ways, depending on model, year and market. Some have only the combined radiator which cools the engine coolant as well as the ATF. Some have a modest coil of atf pipe in front of the radiator in addition, before the atf goes through the main radiator's bottom part. Some have a proper atf cooler (radiator) in front, before the atf goes through the main radiator's bottom part. Some have only an ATF cooler, and no combined radiator.

What you need depends on your use and the climate the car operates in.
One major design aspect of the land cruiser solution, is to actually heat up the ATF to achieve a smooth operation of the transmission earlier after a cold start. (Because the engine heats up faster than the gearbox, on their own). That's why, whatever variation you have, the atf goes through the main (engine's) radiator last, before entering the gearbox. Lockup of the TC will not happen until the atf has reached a certain temperature, e.g., in order to help with the heating up.

If you operate in the UK, where the temperature is normally above freezing (or not far below), you might be ok without having the "heating atf function" which the combined radiator gives. If you end up with a non-OEM radiator, you could go for one without the oil cooler, and instead mount a proper oil cooler for the atf in front. This also depends on which atf you use, as the synthetic fluid is much better at low temps than the mineral version which was standard when this atf cooling (and heating) solution was designed. (And, btw, a synt atf gives smoother gearshifts in any case, and less chance of atf degradation because of heat.)

Radiators do fail, and if you get coolant into the atf, you will need a complete rebuild of the gearbox, which is not cheap. Although this event is not frequent, it still happens, and is an expensive experience. Seems to be more frequent on the 120 than on the 100, e.g., but that might be only in numbers, not as a percentage.

 

[Sam]

Genuine radiators can be ordered from any Toyota dealer in the U.K. They are still in production and available. I got a quote for one this week to replace mine. Just be sitting down when you get the price.

Be intesreded to see if that's true - my local Toyota said mine was out of production and couldn't be sourced. Maybe because it's an '03

 

[Sam]

Just to give another perspective:

Thanks for that detail uHu - appreciated

 

[Tractionman]

Don't know, but would have thought that all the 120's maybe prior to Invincibles would have the same radiator ? If they went by your vin number which would identify year, then that's possibly why they said out of production. Toyota frequently change/update part numbers, so a possibility why they never offered an alternative from another year - different part number?. Just summising.