Help: AT OIL TEMP ISSUE - LX470 (1 Viewer)

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AT OIL TEMP ISSUE: LX470



I just purchased a very clean 2005 LX470 from the Lexus dealer in Henderson NV. 105k miles, 1 owner, seems to drive great. I was very excited …. However, there’s an ongoing issue with the AT oil temp.



Backstory:

I flew to Vegas to purchase. On my first attempt to drive this home to CA from the dealer, the AT oil temp light came on for me. I was only 30 minutes away from the dealer and I drove it back.



The dealer kept the LX for a few days to test and they said they accidentally overfilled it when doing a flush and corrected the issue.



I flew back to to dealer, test drove it again, and it worked fine. I proceeded to head home again. 30 miles outside of the dealer and in traffic the AT oil temp light went on again. The dealer was closing for the day and so I went and bought laser scanner temp gun and an obd2 scanner.



In Vegas, flat ground, traffic and 100 degrees weather: AT oil temp got up to ~280-300. Again, this was within an hour after I purchased the car. The OBD2 code was: P0712 “transmission fluid temperature sensor “a” Circuit Low Input”.



I spend the night in Vegas and the dealer inspected the transmission the next day. Oil was not burned, there was only a normal amount of metal in the pan/filter and everything looked fine”. They did admit that the first two times they changed the transmission fluid, no one on their team changed the filter though. They refilled it, changed the filter, tested it themselves and sent me on my way.



I headed home for the third attempt. It only took an hour of driving and the first big hill for the AT oil temp light to go off again. After that first hill leaving Vegas, I let it cool down and continued the drive home once it was safe. It drove fine the rest of the way.



Side note: Unfortunately I also noticed that the dealer had also turned on the heat during their test drive which probably gave them faulty info during the test (this is concerning if it was intentional to keep it running cooler). I was told that during their last test which was going up a long hill when it was hot out they were around 275 degrees using the live data on their obd2 scanner.





Current details:



Testing back home in CA. I drove partially up a local Mountian and the AT oil temp light came on again. It was 70 degree weather. AT oil temp was 287 - 302 range with light on. And cooled to 238-251 20 mins later once light turned off after resting with engine off 1/2 way up the Mountian.



At home after driving back 1.5 hrs it’s 251-261 in the cool night air.



The light doesn’t come on for normal daily driving, but as soon as something pushes it (traffic and hot weather or go if up a steep long hill) it seems to get to 300 degrees every time.



It drives amazing, shifts perfectly as well. I’m at a loss for what to do here.



Anyone can law ever had this experience before?



I love the truck, it’s supposed to be for adventures. But at this point I can’t even make it to the top of a long steep hill without an AT oil temp issue.



Any help is so greatly appreciated. Thanks so much 🙏🏼.
 

JunkCrzr89

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Those temps seem astronomically high. Mine never gets above 165*F, and is typically between 140-150*F, based on OBD2 reader (not sure if this is at the pan or torque converter). I’m astonished that they sent you on your way after they recorded 275*F.
 
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Those temps seem astronomically high. Mine never gets above 165*F, and is typically between 140-150*F, based on OBD2 reader (not sure if this is at the pan or torque converter). I’m astonished that they sent you on your way after they recorded 275*F.
Thanks for sharing your baseline. To clarify I have been testing using a laser gun on the oil pan.
 

flintknapper

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Thanks for sharing your baseline. To clarify I have been testing using a laser gun on the oil pan.

I've compared oil pan temps (using an IR gun) with the readout on my ScanGauge and they have always been within a degree or two of one another. On my 80 series I have a temp probe in the transmission pan and digital readout gauge. Again...using an IR gun, the two temps agree.

So....IF your temp gun is reasonably accurate....its fair to assume the temps you are seeing are indeed that high.

The temps you cite are high enough to be of serious concern. It is unbelievable to me that any shop would send you on your way with 275°F fluid temps. That is absolutely reckless on their part.

Both transmissions in my vehicles (A343F) (97 land cruiser, 99 LX470) run between 142-165°F in the heat of a Texas Summer.
 
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I've compared oil pan temps (using an IR gun) with the readout on my ScanGauge and they have always been within a degree or two of one another. On my 80 series I have a temp probe in the transmission pan and digital readout gauge. Again...using an IR gun, the two temps agree.

So....IF your temp gun is reasonably accurate....its fair to assume the temps you are seeing are indeed that high.

The temps you cite are high enough to be of serious concern. It is unbelievable to me that any shop would send you on your way with 275°F fluid temps. That is absolutely reckless on their part.

Both transmissions in my vehicles (A343F) (97 land cruiser, 99 LX470) run between 142-165°F in the heat of a Texas Summer.
Thanks a lot for the feedback and details. Shoot, this is seeming like the consensus.
 

flintknapper

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100 Series:

100 series ATF temp.jpg



80 Series:

80 Series Trans Temp.jpg
 
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I don't have an answer for you but here is some info you can tell them tomorrow. More info at TCI Transmission Life Expectancy - https://www.tciauto.com/trans-life-expectancy

How hot is too hot?
The ideal operating temperature for automatic transmission fluid is between 175 and 225° F. At approximately 240° F, important additives in the ATF begin to cook. The result is the formation of varnish inside the transmission. At approximately 260° F, internal transmission seals (which are typically manufactured from a polyacrylate material) begin to harden. The end results are leaks, both internal and external, simply because the seals lose their elasticity. At approximately 295° F, transmission clutch plates begin to slip because the oil is breaking down further. At approximately 315° F, seals and clutches effectively burn out. Carbon forms in the oil and for all intents and purposes, the transmission is junk. Just for your information, a typical transmission will die within 2000 miles if subjected to 300° F+ heat.
 

ramangain

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Try driving with OD off and see if the temps don't spike as high.

You can also try disconnecting the return line on the tranny cooler (if equipped) to see if the flow is too weak, re: blockage.

Additionally, if the P0172 error code keeps returning, you may want to replace that sensor.
 

flintknapper

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Have someone check for blockage in the lines going to and from the Oil Cooler.

At one time my trans suddenly showed higher than normal temps (got over 160°F) and an investigation of that turned up no flow through the oil cooler.

When I dropped one of the lines going to the radiator portion (not the grill mounted cooler) I found what looked to be a shipping plug of some sort.

It just happened to be the exact size of the rubber line. Somehow it managed to turn just right and get in the line and block it.

Using an IR temp gun on the lines and external cooler will tell you in a hurry if there is blockage. Heck...just feeling the lines by hand would as well.

Shipping Plug.jpg

SP.jpg
 

jLB

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Those temperatures sound exceptionally high. I usually see 150-180* and get uncomfortable on the rare occasions that I see low 200s* (usually only with lots of engine braking downhill).

 
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I agree with everyone else; those temps are way too high for standard conditions. Try disabling overdrive and monitor temps.

FYI, I monitor mine using a bluetooth OBD reader, and torque pro.. I usually never see above 160deg in traffic, and cruise right around 140deg on the hwy here in TX. This cheap method of observing temps is well worth the investment IMO
 

suprarx7nut

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I was a little anxious when I saw my temps crest 200F when I was towing the max weight in a trailer up over the continental divide - full throttle for 15 minutes at a time, barely able to go 30mph.

You have a serious problem at 275F and up. I'd be surprised if the trans hasn't already suffered some permanent damage.

I'd be returning the vehicle or demanding that they fix the transmission temp issue. If they can't figure out how to fix it, they should replace the trans or buy back the car.

A 100 should not have a dying trans to worry about. That's not a cheap fix and the drivetrain robustness is the majority of the value of these vehicles. To have a known failing trans in a 100 series is a deal-breaker.
 

ramangain

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I was a little anxious when I saw my temps crest 200F when I was towing the max weight in a trailer up over the continental divide - full throttle for 15 minutes at a time, barely able to go 30mph.
The utter lack of mechanical sympathy these rigs can withstand is amazing, especially when towing.
 

MJK

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I would call up Lexus of Henderson, make sure they understood the situation was not resolved, and that you are declining to adopt the problem.

From there, either push to have it resolved locally at their expense or walk away.
 

Tanner H

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If it were my truck I'd personally drain and fill the pan again correctly. We need to remember that yes, it was at a dealership...but they could have given the job to a rookie there that simply didnt do it right. For all you know, someone there could have looked at trans fluid capacity in their service manual and filled her up and crossed it off their list. They could have also removed the excess plug too early/too late which messed up the levels as well. The fluid needs to be filled up, then run to warm up and there is a small window of time to drain the excess fluid correctly.

Hopefully they gave you some sort of warranty if that process doesnt solve the problem.
 

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