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Discussion Starter · #1 ·
Hey guys i need help with an issue i am facing with my fj



2hi i drive every day and it’s perfect

4lo also no issues

But 10-15 mins after engaging 4hi i get the A/T oil temp light on my dash board



I had this issue then, i replaced gear oil and replaced my gear also still i am facing the same issue again. I also have a 11 inc Hyden gear cooler
 

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You say you replaced the "gear" oil. Did you replace the transmission fluid (ATF) and make sure the level is correct by following the proper procedure? And is the cooler for the auto trans? Did you check the transfer case oil level as well? How many miles and what year is your FJ?

Also, electrical gremlins may be at work. The way to check that out is to find out what the actual auto trans temp is when the light comes on and see if it's actually too high. You can do this either with a OBDII scan gauge that has the PID to read transmission temps, or obtain a handheld IR thermal temperature gun and point it at the transmission pan and measure the actual temperature.
 

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Discussion Starter · #3 ·
You say you replaced the "gear" oil. Did you replace the transmission fluid (ATF) and make sure the level is correct by following the proper procedure? And is the cooler for the auto trans? Did you check the transfer case oil level as well? How many miles and what year is your FJ?

Also, electrical gremlins may be at work. The way to check that out is to find out what the actual auto trans temp is when the light comes on and see if it's actually too high. You can do this either with a OBDII scan gauge that has the PID to read transmission temps, or obtain a handheld IR thermal temperature gun and point it at the transmission pan and measure the actual temperature.
Hey buddy, yes i have changed the AFT fluid properly and i have an 11inc hyden cooler (ill drop the amazon link of my cooler below) . I am not sure if i checked transfer case oil. I have a 2007 fj but i have replaced the engine and gear recently and also replaced the odometer so i am not sure about how many miles my car have done. I even have an obd reader and temperature seems normal to me when i get the AT OIL TEMP light. OIT( i am guessing this is gear oil temp) is 86 degrees and CVT is 95 degrees when i get the at oil temp light.

if i have an electrical issue then even in 4lo i should get AT OIL TEMP light. But it only comes on in 4hi

Hayden Automotive 679 Rapid-Cool Plate and Fin Transmission Cooler , Black , 11 Inch Hayden Automotive 679 Rapid-Cool Plate and Fin Transmission Cooler , Black , 11 Inch: Buy Online at Best Price in UAE - Amazon.ae
 

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So when the light comes on, does it stay on or go out immediately if you shift back into 2hi? Does the light eventually go out if you pull over, put your rig into Park and let the engine idle? What I'm trying to figure out is if you have an actual hot transmission, or an electrical issue. Normal operating trans temp should be between 165 to 185 degrees F. Towing might make it climb up to 220 F. And you're sure the fluid level is OK via the level check plug while the trans is at 130 degrees F at idle? That looks like a nice trans cooler as well.
 

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You say you replaced the "gear" oil. Did you replace the transmission fluid (ATF) and make sure the level is correct by following the proper procedure? And is the cooler for the auto trans? Did you check the transfer case oil level as well? How many miles and what year is your FJ?

Also, electrical gremlins may be at work. The way to check that out is to find out what the actual auto trans temp is when the light comes on and see if it's actually too high. You can do this either with a OBDII scan gauge that has the PID to read transmission temps, or obtain a handheld IR thermal temperature gun and point it at the transmission pan and measure the actual temperature.
Cross-checking warning light vs trans temp reported through OBD won't work as they are both reading the same sensor in the transmission.

One way of cross-checking for an electrical/sensor problem is to look at both the pan and torque converter outlet temperatures through the OBD ... under steady-state cruise conditions they should be within a few degrees of each other, and pan temp can NEVER be higher than TC outlet temp.

OP, when you say the AT overtemp light only comes on in 4H but never in 2H, is the vehicle being driven in EXACTLY the same load conditions when comparing 2H vs 4H?

Absolute first thing I'd verify is AT fluid level at operating temp, and verify that the lines to the aux trans cooler aren't pinched or internally restricted by a chunk of debris.

And clarify: you are running BOTH trans coolers in series, hot ATF from the transmission first passes through the in-radiator cooler, and then through your AUX cooler, and then back to the transmission, correct?
 

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I was trying to verify if the A/T temp light was actually being triggered by hot transmission fluid or something false like a weird computer glitch instead. So I guess checking the actual pan temp with an infrared thermometer would be the only way to really verify a hot trans since the sensor's output reads the same through the OBD connection. His problem is weird, but 4hi does put more strain on the A/T, so if his plumbing isn't correct, it'll overheat. He also needs to verify he got the fluid level correct using the right procedure, because that's critical to keeping the trans cool.
 

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Discussion Starter · #7 ·
So when the light comes on, does it stay on or go out immediately if you shift back into 2hi? Does the light eventually go out if you pull over, put your rig into Park and let the engine idle? What I'm trying to figure out is if you have an actual hot transmission, or an electrical issue. Normal operating trans temp should be between 165 to 185 degrees F. Towing might make it climb up to 220 F. And you're sure the fluid level is OK via the level check plug while the trans is at 130 degrees F at idle? That looks like a nice trans cooler as well.
When i shift to 2h then light goes off after few mins
If the car is idle for 10-15 mins again then the light goes off
 

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Discussion Starter · #8 ·
Cross-checking warning light vs trans temp reported through OBD won't work as they are both reading the same sensor in the transmission.

One way of cross-checking for an electrical/sensor problem is to look at both the pan and torque converter outlet temperatures through the OBD ... under steady-state cruise conditions they should be within a few degrees of each other, and pan temp can NEVER be higher than TC outlet temp.

OP, when you say the AT overtemp light only comes on in 4H but never in 2H, is the vehicle being driven in EXACTLY the same load conditions when comparing 2H vs 4H?

Absolute first thing I'd verify is AT fluid level at operating temp, and verify that the lines to the aux trans cooler aren't pinched or internally restricted by a chunk of debris.

And clarify: you are running BOTH trans coolers in series, hot ATF from the transmission first passes through the in-radiator cooler, and then through your AUX cooler, and then back to the transmission, correct?
4hi i use on sand so the load is higher. I think the fluid level is perfect and i belive the cooler procedure is right
 

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4hi i use on sand so the load is higher. I think the fluid level is perfect and i believe the cooler procedure is right.
OK, so you can't make valid comparison between fluid temperature reached in 2H and 4H if the driving conditions (engine and torque converter loads) are RADICALLY different.

When cruising along in 5th gear in 2H range on pavement, the torque converter lockup clutch will be locked, there will be no fluid 'shear' within the torque converter, and the torque converter itself will be generating almost no internal heat.

When blasting through deep sand in 4H, the lockup clutch will almost invariably NOT BE LOCKED, there will be a huge amount of 'slip' (fluid shear) within the torque converter and a huge amount of heat will be generated within the torque converter.

Get yourself set up to simultaneously monitor BOTH transmission pan and torque converter temperatures (the sensors themselves are built into the transmission) and you can see how TC outlet temperature skyrockets whenever the TC lockup clutch unlocks and the engine is under significant load.


Assuming that your transmission fluid level is correct and your aux transmission cooler is plumbed correctly, then the problem is simply that your driving technique is causing excessive 'slip' in the torque converter, which is heating the fluid to over 300F and triggering the overtemp warning light. You are going to have to manually shift the transmission into 3rd or even 2nd gear to avoid excessive slip in the torque converter.
 

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Discussion Starter · #10 ·
OK, so you can't make valid comparison between fluid temperature reached in 2H and 4H if the driving conditions (engine and torque converter loads) are RADICALLY different.

When cruising along in 5th gear in 2H range on pavement, the torque converter lockup clutch will be locked, there will be no fluid 'shear' within the torque converter, and the torque converter itself will be generating almost no internal heat.

When blasting through deep sand in 4H, the lockup clutch will almost invariably NOT BE LOCKED, there will be a huge amount of 'slip' (fluid shear) within the torque converter and a huge amount of heat will be generated within the torque converter.

Get yourself set up to simultaneously monitor BOTH transmission pan and torque converter temperatures (the sensors themselves are built into the transmission) and you can see how TC outlet temperature skyrockets whenever the TC lockup clutch unlocks and the engine is under significant load.


Assuming that your transmission fluid level is correct and your aux transmission cooler is plumbed correctly, then the problem is simply that your driving technique is causing excessive 'slip' in the torque converter, which is heating the fluid to over 300F and triggering the overtemp warning light. You are going to have to manually shift the transmission into 3rd or even 2nd gear to avoid excessive slip in the torque converter.
When driving in 4hi i just leave the car in 4th gear and shift to 3rd when i am climbing. Do you think Keeping the the car only in 4tg gear even from idle stop is causing the overheating?
 

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When driving in 4hi i just leave the car in 4th gear and shift to 3rd when i am climbing. Do you think Keeping the the car only in 4tg gear even from idle stop is causing the overheating?
It all depends on how much 'slip' is occurring in the torque converter, but yes, by far the moct likely cause of the overheating is that you are in too high a gear for the load when driving aggressively in sand, and a huge amount of heat is being generated in the TC.

During all this driving in sand in 4H the engine coolant temperature stays within the normal range of 185 - 205 degrees, correct?

Next time you're in 4H in the sand, leave the transmission in 3rd gear or even 2nd. Engine RPM will be higher, but heat generated in the TC will be less.

The torque converter has to be seeing really severe abuse to repeatedly overheat, especially if you've got an auxiliary transmission cooler that's correctly connected.
 

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It all depends on how much 'slip' is occurring in the torque converter, but yes, by far the moct likely cause of the overheating is that you are in too high a gear for the load when driving aggressively in sand, and a huge amount of heat is being generated in the TC.

During all this driving in sand in 4H the engine coolant temperature stays within the normal range of 185 - 205 degrees, correct?

Next time you're in 4H in the sand, leave the transmission in 3rd gear or even 2nd. Engine RPM will be higher, but heat generated in the TC will be less.

The torque converter has to be seeing really severe abuse to repeatedly overheat, especially if you've got an auxiliary transmission cooler that's correctly connected.
Would a converter lockup kit like this solve the problem? GENII Torque Converter Lockup Control Kit to suit Toyota FJ Cruiser 5 Speed
 

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Manual over-ride of the lockup clutch isn't really intended for use in severe high-load, 4WD offroad conditions, but for conditions like towing on pavement where varying road or traffic conditions have the lockup clutch repeatedly locking and unlocking.

Assuming that his transmission cooling system is functioning correctly, all the OP needs to do to eliminate transmission overheating is to manually shift the transmission into the correct gear for the load conditions.
 

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Discussion Starter · #14 ·
It all depends on how much 'slip' is occurring in the torque converter, but yes, by far the moct likely cause of the overheating is that you are in too high a gear for the load when driving aggressively in sand, and a huge amount of heat is being generated in the TC.

During all this driving in sand in 4H the engine coolant temperature stays within the normal range of 185 - 205 degrees, correct?

Next time you're in 4H in the sand, leave the transmission in 3rd gear or even 2nd. Engine RPM will be higher, but heat generated in the TC will be less.

The torque converter has to be seeing really severe abuse to repeatedly overheat, especially if you've got an auxiliary transmission cooler that's correctly connected.
Is there a possibility of low transfer case oil
A friend of mine told me that and ill get that checked soon
 

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While there might be a possibility that your transfer case is low on oil, that would have no bearing on overheating the automatic transmission.

It seems like you are not accepting the fact that driving under high load conditions in the wrong gear can cause the transmission to overheat, and are looking for other 'causes'.

Why not just drive your vehicle in 4H range under exactly the same conditions that previously triggered the overtemp warning light, except this time manually shift the transmission into 3rd gear and leave it there and see if overheating again occurs?
 

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Discussion Starter · #16 ·
While there might be a possibility that your transfer case is low on oil, that would have no bearing on overheating the automatic transmission.

It seems like you are not accepting the fact that driving under high load conditions in the wrong gear can cause the transmission to overheat, and are looking for other 'causes'.

Why not just drive your vehicle in 4H range under exactly the same conditions that previously triggered the overtemp warning light, except this time manually shift the transmission into 3rd gear and leave it there and see if overheating again occurs?
I feel like you are right, so let first try leaving the transmission in 3rd gear in 4hi and try, i just wana know few things so that i am always on the right gear
1. When starting from stand still (0 km/h) should is it fine to be on 3rd gear or i go from L to 2nd then 3rd and leave it there
2. When moving at higher speed can is it fine to go to 4th gear?
3. Somtimes i am in a situation where i stand still inside a bowl and i have to floor it to get out, in this situation is again should i be starting from L or 3rd gear is safe for the transmission ( ik the car will get out on 3rd gear as well)

i also have an 2018 4 runner and i dont have heating issues as i drive it on 3rd and 2nd gear only because it little heavier than fj, so i am hoping that doing the same for my fj will solve my issue
 
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