Wholesale Automatics A442F valve body. (1 Viewer)

[Dusten]

So no one knows why that trans runs hot? What is hot? Why would Toyota allow it to run hot when they know heat is what kills an auto? I’m seriously interested in the answer.

Extended periods in 3rd gear will bring the temps to between 275 and 300.

Cruising with the converter locked up runs around 160

This is all based on posts here.

A good valve body that allows 3rd gear lock up and adding a trans cooler helps. The diesels with the hydro a442f only use the radiator and have no other means of cooling.


Why does Toyota allow this? **** if I know man.


So to answer your questions
Convert stall speed and slippage coupled with a lack of cooling is why it's hot.

Hot is 275-300

I don't know.

 

[Dusten]

It's been noted that kicking down to 2nd and bringing the revs above 2600 seems to help as opposed to third and 2000-2200.

 

[jellis]

Well you ABSOLUTELY need to install an air-to-air cooler in the HDJs! This is such a cheap, easy, and important addition it should be on the top of the list for these rigs. I have mine in-line with my radiator (air-to-air first to reduce temps, then air-to-water in radiator to bring them back up in winter for proper operating temp for the tranny). So in response to @baldilocks, it's probably not the tranny just the difference in cooling systems that's affecting the temps.

Interesting to note, after I got my rig my tranny would get really hot and the light would come on, despite the air-to-air cooler. After I installed an actual gauge I discovered that fortunately my sensor was screwed up and coming on at 235 instead of 302--but it was still running quite hot. One time after a long grade I put my hand on the air-to-air the PO had installed and realized that the entire top half of it was cool and the bottom was wicked hot. The PO had installed it SIDEWAYS, so basically the fluid was short-circuiting across the cooler and it was doing almost nothing. I rotated it 90 degrees so it's now like our radiator, hot in at top and cold out the bottom. That made a HUGE difference.
If an air-to-air cooler doesn't help with temps, it's probably a bad torque converter or tranny. I replaced my tranny with a rebuilt unit last summer and an new OEM torque converter and my temps are much lower. I also used Amsoil ATF, so maybe that's the reason.....can't tell with so many changes at once. Now it takes a serious, slow 4x4 grade while towing my 4,000lb trailer to hit 200-210.....and I definitely always use 4L for converter lockup when doing these kinds of climbs.

One thing that is SUPER interesting about these mechanical diesel rigs is the interplay of tuning and transmission. Installing a new tranny with the WAT VB made my EGTs higher because the engine now revs lower than it used to in order to achieve the same power output. Adding a 25psi turbo reduced transmission temps because I could maintain a higher speed/gear at the same EGT on a grade = less rpm = lower tranny temp.

 

[baldilocks]

Well you ABSOLUTELY need to install an air-to-air cooler in the HDJs! This is such a cheap, easy, and important addition it should be on the top of the list for these rigs. I have mine in-line with my radiator (air-to-air first to reduce temps, then air-to-water in radiator to bring them back up in winter for proper operating temp for the tranny). So in response to @baldilocks, it's probably not the tranny just the difference in cooling systems that's affecting the temps.

Interesting to note, after I got my rig my tranny would get really hot and the light would come on, despite the air-to-air cooler. After I installed an actual gauge I discovered that fortunately my sensor was screwed up and coming on at 235 instead of 302--but it was still running quite hot. One time after a long grade I put my hand on the air-to-air the PO had installed and realized that the entire top half of it was cool and the bottom was wicked hot. The PO had installed it SIDEWAYS, so basically the fluid was short-circuiting across the cooler and it was doing almost nothing. I rotated it 90 degrees so it's now like our radiator, hot in at top and cold out the bottom. That made a HUGE difference.
If an air-to-air cooler doesn't help with temps, it's probably a bad torque converter or tranny. I replaced my tranny with a rebuilt unit last summer and an new OEM torque converter and my temps are much lower. I also used Amsoil ATF, so maybe that's the reason.....can't tell with so many changes at once. Now it takes a serious, slow 4x4 grade while towing my 4,000lb trailer to hit 200-210.....and I definitely always use 4L for converter lockup when doing these kinds of climbs.

One thing that is SUPER interesting about these mechanical diesel rigs is the interplay of tuning and transmission. Installing a new tranny with the WAT VB made my EGTs higher because the engine now revs lower than it used to in order to achieve the same power output. Adding a 25psi turbo reduced transmission temps because I could maintain a higher speed/gear at the same EGT on a grade = less rpm = lower tranny temp.

I think you said that the HDJ does not have an air to oil cooler from the factory. Now that would be odd. Also, your fluid needs to flow through the water to oil cooler first because water/coolant to oil coolers affect the oil temp much more quickly and profoundly than does an air to oil cooler.
FZJ’s are set up this way, my Dodge Cummins is set up this way. In fact, my dodge has a dedicated coolant to trans fluid cooler mounted to the left side of the engine block.

Yours is plumbed backwards. When you are working your trans hard the fluid off the converter is much hotter than engine coolant temps. This is why 180-190 degree coolant can quickly absorb heat from the trans oil bringing oil temp down to a predicted temp that the air to oil cooler can then handle. I suppose the coolant to oil cooler does just the opposite in very cold climates as in very cold. In this case blocking a portion of the air to oil cooler would be a good idea.

 

[Douglas S]

I think you said that the HDJ does not have an air to oil cooler from the factory. Now that would be odd.

It's a fact, at least on the early models. FZJ cooler and hard lines bolt on.

The HDJ81 was only sold in Japan, maybe Toyota didn't consider it necessary for use there? I certainly consider it necessary for use in North America.

 

[jellis]

I was pretty sure I plumbed it according to factory routing. Regardless, if it's wrong it's much easier to run it backwards (A2A then W2A) than worry about it getting too cold in winter/blocking off A2A in winter--or even more absurd, doing it in one day like when I go from my home to my land in AZ I can leave in -10F and arrive in 80F with huge climbs the whole way!
From an engineering perspective it would actually make sense to take hottest fluid and use the least-efficient cooler first because your heat transfer is highest/most efficient when delta T is largest which would be A2A first. Then when delta T is lowest you use the most efficient heat exchanger--and as a bonus in this case the radiator functions just like thermal mass either cooling or heating depending upon what it needs after the A2A.

 

[baldilocks]

It's a fact, at least on the early models. FZJ cooler and hard lines bolt on.

The HDJ81 was only sold in Japan, maybe Toyota didn't consider it necessary for use there? I certainly consider it necessary for use in North America.

Thanks for the clarification. This all starting to make some sense.

 

[baldilocks]

I was pretty sure I plumbed it according to factory routing. Regardless, if it's wrong it's much easier to run it backwards (A2A then W2A) than worry about it getting too cold in winter/blocking off A2A in winter--or even more absurd, doing it in one day like when I go from my home to my land in AZ I can leave in -10F and arrive in 80F with huge climbs the whole way!
From an engineering perspective it would actually make sense to take hottest fluid and use the least-efficient cooler first because your heat transfer is highest/most efficient when delta T is largest which would be A2A first. Then when delta T is lowest you use the most efficient heat exchanger--and as a bonus in this case the radiator functions just like thermal mass either cooling or heating depending upon what it needs after the A2A.

My posts are based on empirical data. The info you provided here has me considering simply swapping the cooler hoses on the metal tubes that come from and lead back to the trans which are mounted to the drivers side of my engine block. They are an inch apart (maybe the HDJ’s are there as well) so swapping the hoses thereby reversing the flow of trans oil through the cooling circuit would be a snap. This would provide me with a fun experiment and additional data.

Even though the winters in Southern WA are mild my trans oil temp, as measure in the oil pan, rarely rise above 120 -130 during normal driving and the gauge barely moves off of the low mark of 100f on a short 6 miles run to town and back home. They say the desirable low is about 140f. Perhaps swapping those hoses to reverse fluid flow would be prudent during colder months.

 

[Dusten]

I posted that earlier. The only cooler they have is the radiator.