Transmission temp question: what is "too hot"

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Wanted to ask a general question about what is "too hot" for a transmission temp. I guess the follow-up question would be: what should I do about it.

When I do big climbs on logging roads (~30kmph), the trans temp quickly rises to about 250 degrees. It seems to level out there if I keep the speed consistent, but it can rise higher than that from time to time. Considering the guage tops out at 280, I think 250 is pretty hot. Is that "hot" or OK?

As a work around, i drop down into Low and its all ok... its just a pain because I have to keep switching back and forth to L and H range whenever the road levels out. All my peeps seem to bang along in 4H which makes me think there is something up with my truck.

I'm driving an HDJ81 (1HDT engine), 35" all terrain rubber, stock gears, intercooled, auto trans. Assuming that 250 degrees is hot, what is the best course of action: re-gear, A/T cooler, get smaller tires (please say no!)?

Thanks in advance for your perspective.
 

S.CarolinaFZJ80

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Get an auxiliary AT cooler. 250F seems way too high based on my experience but where is your temp probe located? On the pan? If so, that might explain the higher temps.

On my US spec automatic 4.5L, the hot trans fluid goes into the bottom of radiator to start cooling then through a factory auxiliary cooler before going back to the transmission.

My Trans temps are usually around 160F cruising in high gear.
While in stop and go traffic and on the trail the temps will rise due to the trans shifting can get up to 200-210F using an ISSPRO gauge with temp probe on trans out line right before it enters the radiator.

Hope that helps give you a comparison.
 

FJRanger

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I'm driving with an auto and 1HDFT. It's easy to see those same temps if I'm not careful, especially when towing or in sand. The auto is electronically controlled and has the a Wholesale Automatic's lockup switch which helps me keep the temps under control. It has the toyota aux. cooler and something I'm considering is a trans cooler with a fan. Derale and B&M make units with a temp sender that activates at a certain temp.

The cruising temp are similar to S.CarolinaFZJ80 and as long as I'm able to keep it in lockup the temps remain where they should.
 

Dave 2000

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Not an automatic lover personally but that aside, is it worth looking at the operating spec for your gearbox oil choice, you might be able to get a better oil? Other than that read on:

I had a Jeep in the other month that had the fluid contaminated from the rad cooler, despite flushing the Jeep trans three times the temps were still a tad too high using a seriously expensive oil. Finally after the fourth flush (and filter change) the temperatures remained stable, this meant that even a very very small amount of moisture in the system allowed the trans to heat up. Would a fluid and filter change/flush be in order, when was the last time it was done? I am no auto specialist but if I said that 9 out of 10 problems I see from not engaging gear when cold/rough shifts/overheating et al were rectified by a couple of changes/flushes it would not be an exaggeration.

regards

Dave
 

Squash

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Short term solution check and/or change your transmission oil, 250 is doable but you need to change oil more often.
How are the engine temps? Higher engine temps= higher tranny temps, just because we sometimes tune our engines!!!

Lastly look for an aux tranny cooler
 
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The engine temps are always fine - although I am only looking at the factory engine temp and EGTs. Its just the Trans temp that concerns me. I have an ISSPRO guage (trans; EGT; turbo), but I dont know where the previous owner installed the probe. I will investigate.

Cruising around the city, or on the highway never yields high trans temps, it just those long climbs.

Oh - and the trans fluid changed about 10,000km ago by the previous owner. (at shop).

I am going to do an oil change in about a month, so I can change the trans fluid then too if need be.

Thanks very much!
 

NCFJ

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I would invest in a good AUX trans cooler with a fan like mentioned above. I would route the coolant through the AUX first and remove the OEM AUX out of the loop. A unit like the B&M with fan will cool the ATF enough before going into radiator that you may even see a reduction in over all engine temp. Tis takes a big load off the radiator

There are many Ultra 4 race vehicles running built auto trans rigs with this cooling system. Do yourself a huge favor and convert your system over to something like -6 AN fittings. It will run you around $8 a fitting average to figure cost, don't know the price of hose off the top of my head. The benefit here is that you will have a system that is very tight and is totally rebuildable and you can re configure with ease down the road if needed. When you blow a hose all you need is a length of hose and odds are you'll have some laying around. Oh yeah, tape the ends so mud wasps don't build nests in the ends. :)
 

SmokingRocks

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34996d1331154329-transmission-temp-trans-life-expectancy.jpg
 
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Just checked out the Derale coolers. Look very nice, and easy to install. The A/T chart is very helpful - definitely looks like my trans needs some extra help cooling.

Thanks again,
Jamie.
 
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... I'm driving an HDJ81 (1HDT engine) ...

Is it equipped with the factory towing cooler? All of the NA market ones came equipped, not as common in other markets? They are very good coolers, if it doesn't have one, it's bolt on and would retrofit a stock unit from a partout rig.
 
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too hot or too cold is not good, 175f to 210f is a good operating range, synthetic trans fluid would be better suited to your high temps, it will take 15 to 20 litres to fully flush and change it. If you ever take the transmission out look at getting it modified to having a lower stall speed, it wont generate as much heat if its not slipping as much, and be careful using that lock up switch as it can damage the converter if you use it under high load (like towing thru boggy sand) it may be worth doing a stall speed test on the converter.
 

FJRanger

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too hot or too cold is not good, 175f to 210f is a good operating range, synthetic trans fluid would be better suited to your high temps, it will take 15 to 20 litres to fully flush and change it. If you ever take the transmission out look at getting it modified to having a lower stall speed, it wont generate as much heat if its not slipping as much, and be careful using that lock up switch as it can damage the converter if you use it under high load (like towing thru boggy sand) it may be worth doing a stall speed test on the converter.


@SeaJay Regarding the lockup switch, I have heard/read this before and sometimes wonder if my converter is already going. I don't engage it until the temps hit 210, if not engaged the temps will keep climbing. I use it as little as possible, but when driving through the mountains it almost feels like I'm driving a manual without working the clutch.

From what Rodney told me, well at least what I remember, is during lockup the Toyota converter stops pumping fluid and the heat continues to build inside it. My understanding is Wholesale Automatic's billet converter helps solve this problem by continuing to allow the fluid to move throughout the entire system. Please correct me if I'm wrong as it's been a couple years since I spoke with them.
 
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Converters don't pump fluid, that is the job of the front pump (the part the nose of the converter spins). During lock up pressure is applied to the converter lock up clutches this stops the "slip" in the converter and makes it 1:1 (ideally). If there is slippage in the converter clutch it will generate a lot of heat very quickly.
 

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