Transmission Overheated

[Elapid100]

Hi Folks,

Been lurking for a few months but just registered. I have an '06 LX470 that I purchased November 2013 with 125K. Very well maintained, one owner, full service records and original owner bought new, serviced, and traded it in to the same Lexus dealership that I picked it up pre-owned from.

Last month, I took a trip from Southern California to the Grand Canyon and about 30 minutes outside of the Grand Canyon, I exited off Interstate 40 at Williams and dove into the first gas station I saw because the girls had to use the restroom. Parked at the pump, fueled up, and then the car would not turn over. Check engine light and AT Temp light was on. Tried a couple of times to no avail, and I ended up parking the car for 2 hours hoping it would cool off, and sure enough it did and I was able to start the car and drive it normally for the rest of the trip. As soon as I got back to the big city, I took it to Lexus to get the transmission checked out. They said no damage, but the fluid was indeed burnt and they flush & filled it. The service manager and I looked up the full service records in detail and we saw that there was no written record of the transmission ever having been serviced at all, which was super strange because the car literally had service records for every Lexus recommended interval.

To this day, I am unsure if the AT was actually serviced at 60k and never again until my incident, or if it had been sealed the entire time since it left the assembly line. In any case, it seems like my transmission reached the end of its useful life and was no longer able to shed heat. Obviously not a surprise. I'm actually glad it happened, because there's no telling how much longer I would have driven around with old trans fluid.

FWIW, it was July in Arizona. Air temp was 100+ at 3pm in the afternoon. I had just climbed up a medium sized grade at around 65 MPH (loaded with camping gear but not towing) and then at the top of the hill was the freeway exit and immediately after the exit I stopped and of course the AT fluid didn't have time to cool down and just sat there boiling itself for 10 minutes.

I am mildly irritated that there was no warning at all, so it seems like the AT Temp warning lamp is a full-on idiot light. Would have been better to warn me first before it overheated

 

[hoser]

2004-2007 use WS "lifetime" fluid and there is no change interval. Mud advice is to change anyway at 90-100k intervals... 60k, if towing.

 

[TXLX100]

That is strange, haven't heard of that. Also strange that it wouldn't start, I would think that it would start regardless. Did it crank but not start or no crank at all? I've operated mine (and everyone else I'm sure) in pretty extreme heat and hard use and never had a heat problem.

You may want to invest in a OBD2 monitor so you can watch the trans temp for a while.

 

[CappyKD]

That is strange, haven't heard of that. Also strange that it wouldn't start, I would think that it would start regardless. Did it crank but not start or no crank at all? I've operated mine (and everyone else I'm sure) in pretty extreme heat and hard use and never had a heat problem.

You may want to invest in a OBD2 monitor so you can watch the trans temp for a while.

Agreed.

How is your fan clutch?

 

[Muddy Bean]

I might confuse the issue, but aren't there other reasons that AT light comes on other than temp issues?

 

[Elapid100]

That is strange, haven't heard of that. Also strange that it wouldn't start, I would think that it would start regardless. Did it crank but not start or no crank at all? I've operated mine (and everyone else I'm sure) in pretty extreme heat and hard use and never had a heat problem.

You may want to invest in a OBD2 monitor so you can watch the trans temp for a while.

Yes - it cranked, but just would not start. With the key inserted in the ignition and during cranking, the lights that were illuminated on the dash were the check engine light and the AT Temp fluid light. I cranked it 3 separate times, waiting a minute or two between each attempt - all to no avail.

With the AT Temp light on, and since the engine was cranking, and I saw no fluid leaks under the car or in the engine bay and no obvious signs of any damage and plenty of coolant in the tank, I assumed the trans had in fact somehow overheated and that's why I decided to park it for a few hours and try again after the sun got lower, and sure enough that did the trick.

When the Lexus dealer pulled the codes and checked the car, they didn't see anything except the transmission had overheated and they said that it was obvious the transmission fluid was burnt. The good news is there was supposedly no permanent damage. The bad news is I still don't know why this happened in the first place. I wasn't towing and only had myself and my co-pilot in the car. We had maybe 300 pounds of camping gear and supplies, nothing on the roof, and the 3rd row seats removed. Car was a lightweight essentially. Being in 100-110 degree desert temps and even climbing a few thousand feet on freeways should have been nothing for this car, but somehow the trans overheated with no warning.

As for an OBD2 monitor, that's a great idea and I'll definitely look into it. Is there a popular OBD2 that folks prefer?

 

[Bombdefuzer]

I have been using Scangauge II and it is very informative.

 

[Elapid100]

I have been using Scangauge II and it is very informative.

Roger that. Just did some search on the Scanguage II here and also on their website and it does seem like transmission temp is supported.

Also, according to the FSM that I just downloaded, in the Diagnostic section on page 604, it appears the ATF temp sensor trips at 266 degrees F. So I must have been at or above 266 for the ECU to not even allow the engine to turn over. Holy cow.

I also just now remembered that when I took it to the Lexus dealer, it took them about 3 hours of putting a fan under the car on the lift in order for the trans temps to cool down enough where they could work on that car. And that was on just a short 20 minute drive to the dealer in an empty car with no hills (now granted the desert air temp was 120 degrees F on that day, but still).

 

[CappyKD]

Roger that. Just did some search on the Scanguage II here and also on their website and it does seem like transmission temp is supported.

Also, according to the FSM that I just downloaded, in the Diagnostic section on page 604, it appears the ATF temp sensor trips at 266 degrees F. So I must have been at or above 266 for the ECU to not even allow the engine to turn over. Holy cow.

I also just now remembered that when I took it to the Lexus dealer, it took them about 3 hours of putting a fan under the car on the lift in order for the trans temps to cool down enough where they could work on that car. And that was on just a short 20 minute drive to the dealer in an empty car with no hills (now granted the desert air temp was 120 degrees F on that day, but still).

That seems abnormal.

I have driven mine on 110 degree days and have never seen trans temps above 180 with my scangauge II and that is after 3 mile climb up a very steep grade and then 3 mile decent down the other side with no foot on the gas or brake, essentially engine braking the whole way down. (heats the trans up good.) under normal conditions on a 105 degree day without the hill climb I sit in the 150-160 range.

 

[TeCKis300]

That seems suspect that the trans would heat up that dramatically under what I'd consider, pretty nominal use. I've done serious climbs with my '06, towing ~6000lbs, heavy throttle, heavy engine rpms for probably a 15-20 min climb in almost 100 degree heat. Everything just dandy.

I would suspect something is wrong. I'd check that the tranny cooler is not blocked for whatever reason. I'd also suspect the torque converter. Perhaps the lockup function is not working and artificially heating up the fluid?

 

[Sligex]

I'd also suspect the torque converter. Perhaps the lockup function is not working and artificially heating up the fluid?

Hang on, I didn't think our LC's/LX's had locking torque converters? From what I understand, they're only high-stall converters... (from reading documentation on the A750F)

 

[CappyKD]

Hang on, I didn't think our LC's/LX's had locking torque converters? From what I understand, they're only high-stall converters... (from reading documentation on the A750F)

Not accurate info.

West Coast Cruisers sells this: (They make upgraded valve bodies, torque convertors and other trans and transfer parts for Aussie use with a SoCal distributor.)


Manual Control Lock-Up Unit Toyota with A442F, A343F, A750F, and soon for the B02A(6 speed auto) transmissions. Designed to manually control the Lock-Up convertor in All forward gears and reverse(Require Extreme Valve Body for 1st and Reverse Lock-Up). Eliminates all convertor slippage and convertor runaway on steep downhill descents allowing full 100% engine braking. These are must for Off-road Enthusiasts as well is those who Tow.
$210.00 USD (In Stock)



http://westcoastcruisers.com/transfer.php

 

[re_guderian]

Very strange, indeed. '06 seems to have a lot of "no start issues". Search here. Based on the B.S. story from the dealer about three hours on a lift with a fan to cool it down, I'm doubting their certain assessment of "burnt" fluid, too.

 

[Elapid100]

Thanks for all the feedback so far. Money is a bit tight this month but I should be able to pick up a Scangauge next month and will report back with my findings.

I agree that none of this really makes a whole lot of sense. That said, when doing searches here for ATF and fluid temps, there have been other posters here previously that had reported seeing 200+ degrees ATF temps. So although 200+ is abnormal, it does seem like others have had it happen in conditions that also wasn't overly demanding. In my case, I must have been running 200+ degree ATF temps when I parked the car and without airflow it must have just sat there sky rocketing past the AT Temp warning trigger.

 

[GaFJC]

I have a scan gauge II and have seen temps approach or slightly exceed 220 degrees with steady elevation climbs on fire roads. I was unloaded except for a passenger (and our fly fishing gear - nothing else). Was traveling at speeds of 15 to 20 mph thru a heavily forested and graded fire road. I am guessing that outside temps were In the low 80's. I am running Amsoil with less than 20k easy miles. The AT temp light didn't come on but the steady AT fluid temp increase made me wonder if the fan clutch could be worn out or if the aux fan wasn't working.

Here's an example of norms; generally highway speeds of 70 to 80 mph, unloaded, outside temps of high 80's to low 90's, and elevation gain of 1500 ft in 2.5 hours sees a steady 160 to 165 degrees. Maybe 170.


...via IH8MUD app

 

[04UZJ100]

What gear were you in when climbing at 65? If in fifth you were probably unlocked just shearing the fluid in the torque converter. Next time, make sure you're in 4th. The revs will be in the sweet spot for torque and the torque converter will lock. No shearing, no heat.

 

[Elapid100]

I picked up a ScanGuage II yesterday, hooked it up today, and then programmed in the X-Gauge. Will start logging my ATF data and report back with my findings.

What gear were you in when climbing at 65? If in fifth you were probably unlocked just shearing the fluid in the torque converter. Next time, make sure you're in 4th. The revs will be in the sweet spot for torque and the torque converter will lock. No shearing, no heat.

Good question! I left the transmission completely alone in D the entire time. I suspect what you described was most likely a major contributing factor.

 

[Kofoed]

Not accurate info.

West Coast Cruisers sells this: (They make upgraded valve bodies, torque convertors and other trans and transfer parts for Aussie use with a SoCal distributor.)


Manual Control Lock-Up Unit Toyota with A442F, A343F, A750F, and soon for the B02A(6 speed auto) transmissions. Designed to manually control the Lock-Up convertor in All forward gears and reverse(Require Extreme Valve Body for 1st and Reverse Lock-Up). Eliminates all convertor slippage and convertor runaway on steep downhill descents allowing full 100% engine braking. These are must for Off-road Enthusiasts as well is those who Tow.
$210.00 USD (In Stock)



http://westcoastcruisers.com/transfer.php

Is that just a wired switch, fuse and relay for $210????

 

[CappyKD]

Is that just a wired switch, fuse and relay for $210????

Essentially. That and the knowledge of how to wire it correctly without trashing your Trans, TC or trans ecu in the process.

 

[CappyKD]

You are also paying a premium as it is coming from AUS.