Should I put an external trans cooler in my GX460?

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swild

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We all know the GX460 can have transmission issues when transmission temperatures get too hot for too long.
But if I live in Southern California and don't tow, is it really worth installing one? I take annual road trips and might have the GX fully loaded during those trips, but is a trans cooler really necessary?
 
Absolutely necessary. I would also add an inline filter and a way for you to monitor torque converter temps and pan temps. Monitoring torque converter lockup also helps with transmission temps.
 
Is there an issue with the transmission fluid temps being too cool? Will the trans cooler cause other problems?
 
The GX460 transmission has its own thermostat that fully opens at around 190F. There shouldn't be any risk of it running too cool.
 
So, what is the most popular cooler to get, the Hayden 678 or 698?
 
I have a 678 in mine since the transmission already has a thermostat. Some people get the 698 and pin the thermostat in the transmission. I think the 698 thermostat opens at a lower temperature.
 
I would first suggest replacing the OEM radiator with a CSF aluminum radiator. That gets you a better radiator that should not crack/fail in the future, AND get you a better integrated trans cooler. I already had an external cooler when I upgraded to the CSF, but was still shocked at how much lower the radiator made trans temps (they stopped spiking when the torque converter unlocked). You can then watch your trans temps and decide if you also want an external cooler (or, just do both at the same time). If you are towing or wheeling at all (even if just a few times a year) I would suggest the CSF radiator AND an external cooler.

I had a Hayden 678 originally and upgraded to a 698. If their internal thermostat is working, I can't tell. It still over-cools in cold weather, and I have the cooler mostly blocked off now with a sheet of rubber. So I'd just get the 678. I have a GX470 that does not have it's own integrated trans thermostat.
 
As far as overcooling, I dont think you can in socal. If you frequently road trip to cold places, then different story.

I saw my TC lock up when trans temp was 115F. if it can lock up, then it's good enough operating temp.
 
A bit of an exaggeration to say a trans cooler is critical on a GX that doesn't tow or go off-road. On the highway your converter is locked and you have plenty of airflow. Not necessary.

If you're towing or doing serious off-roading, absolutely.
 
swild said:
So, what is the most popular cooler to get, the Hayden 678 or 698?
Click to expand...
I put a 678 on mine about 2 years ago and pinned the thermostat open. In Texas summers, I generally run around about 180-185 after fully warming up and creeps up to 200-210 sometimes. Not bad at all.

IMG_5827.webp
 
alhounos said:
A bit of an exaggeration to say a trans cooler is critical on a GX that doesn't tow or go off-road. On the highway your converter is locked and you have plenty of airflow. Not necessary.

If you're towing or doing serious off-roading, absolutely.
Click to expand...
If you are pulling a large grade where you can't get into 3rd gear, the TCC will stay unlocked and the trans temps will start to run away. I've had this happen on 2-lane twisty mountain roads and in 4-Lo when going up off-road passes. Both times I was basically unloaded other than tent camping gear and people. And, my GX470 had a small undersized external cooler. BUT, that only happens out West. It has not happened here in the middle of the country where our hills are much shorter.

I understand the TCC will eventually lock up on a GX460 if the trans gets pretty hot, but it may be too late at that point.

But...CSF radiator should do a lot to solve that problem on a non-towing rig, without adding a cooler.
 
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My pan temps were hitting ~220 on long mountain passes before adding the Hayden. After adding a cooler, they stay under 200. Even if you’re not towing, reducing heat helps longevity. These transmissions don’t love sustained high temps.
 
swild said:
Is there an issue with the transmission fluid temps being too cool? Will the trans cooler cause other problems?
Click to expand...

swild said:
So, what is the most popular cooler to get, the Hayden 678 or 698?
Click to expand...

alhounos said:
A bit of an exaggeration to say a trans cooler is critical on a GX that doesn't tow or go off-road. On the highway your converter is locked and you have plenty of airflow. Not necessary.

If you're towing or doing serious off-roading, absolutely.
Click to expand...

The hottest my ATF has been is sitting in bumper to bumper traffic in a construction zone before customs going into Canada. Second hotest was after going up a bluff where ATF pan temp started to rise then had to sit at a stop light at the top carrying a half ton of lead shot for reloading in the back. No air flow both times. Mn. has 2 seasons winter and road construction with a lot of sitting on the highway during road construction.

Lived in San Diego in the 70's when I was stationed there for 4 years and there was a lot of stop and go traffic back then. Going to go out on a limb and say it likely hasn't gotten much better since LOL.

I went with the 698 because of concern of over cooling. If you live in the coldest spot in CONUS where they warn of exploding trees because it is in the -20° below zero temperatures I feel the 698 is a better choice.

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Otherwise a 678 should be fine. I would also pin the ATF warmer open all year down there. I pin mine open in the Spring and pull the cotter pin in late Sept. so that it functions as intended. Pretty much in sync when they start to treat diesel fuel to prevent it from gelling.

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Cell phone screens will stop working when they freeze up at ~10 above zero so haven't really tracked below that. But at 14° I will idle for at least 10 minutes to warm up.

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Drive to town for groceries then after coming back so 13 mile round trip. ATF temp is good.

54209559286_ef87faaa85_b.jpg
 
swild said:
We all know the GX460 can have transmission issues when transmission temperatures get too hot for too long.
But if I live in Southern California and don't tow, is it really worth installing one? I take annual road trips and might have the GX fully loaded during those trips, but is a trans cooler really necessary?
Click to expand...
Yes, with the stock heat exchanger functioning and no auxilary cooler the A760F in the GX460 runs 200+ degrees driving empty down a flat interstate in 70+ degree weather. This is too hot for 60K service intervals much less lifetime fill, IMO.

swild said:
Is there an issue with the transmission fluid temps being too cool? Will the trans cooler cause other problems?
Click to expand...

A transmission running 130 degrees will outlive a transmission running 200 degrees every time if they are on the same maintenance schedule.
The condensation thing is a total non-factor unless you just never take an extended drive.

With a Hayden 678 and the heat exchanger bypassed I see:

Unloaded (steady interstate, fully stabilized)​


Ambient (°F) - A/T Oil Temp 1 (°F)
20 - 25 130 – 135
30 - 35 140 – 141
50 – 55 148 –151
85 – 90 165 –170
90 - 95 171 max observed
 
Anything below 150F is too low, IMO. My A750F shifts hard at low trans temps. I put a rubber cover over 2/3 of my Hayden cooler in the winter, which gets the temps up to closer to 150-160F. It needs to be summer for mine to hit 170F.
 
Rednexus said:
Anything below 150F is too low, IMO. My A750F shifts hard at low trans temps. I put a rubber cover over 2/3 of my Hayden cooler in the winter, which gets the temps up to closer to 150-160F. It needs to be summer for mine to hit 170F.
Click to expand...

My A760F shifts smoothly at from any temperature I've driven it thus far, pan temps ranging from 50 degrees to 200 degrees (before installing Hayden and bypassing).
The pan temp actually makes very little difference in shift quality with mine, and I can say this as I've gotten to the point I'm monitoring the OBDlink every time I drive it and I'm really scrutinizing everything as I learn the truck.

I run Aisin ATF-0WS and have done 5 drain/fills (including filter change) over the last 10,000 miles, FWIW.
 
BC11SVT said:
My A760F shifts smoothly at from any temperature I've driven it thus far, pan temps ranging from 50 degrees to 200 degrees (before installing Hayden and bypassing).
The pan temp actually makes very little difference in shift quality with mine, and I can say this as I've gotten to the point I'm monitoring the OBDlink every time I drive it and I'm really scrutinizing everything as I learn the truck.

I run Aisin ATF-0WS and have done 5 drain/fills (including filter change) over the last 10,000 miles, FWIW.
Click to expand...
I should disclose that mine has a Nomad valve body in it :). Could certainly be the reason, as it shifts firm when it's warm and relatively hard when it's cold. If you are going all-in on GX mechanical upgrades, the Nomad is a good one.
 
Just to throw my .02¢ in the mix.
I have a very heavy rig (R²M 2013 GX 460 Overland Build) that's been built since 2018m with about 128,000. I do not tow and I do not run a trans cooler. Albeit, I do monitor trans temperatures with my OBDLink in real time as I'm driving, especially when going up long steep grades.
I usually manual shift, when temps start to rise. Changed my trans fluids at 90k and scheduled to do it again at 140k.
 
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