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I am planning on a move from Washington to SoCal (1200 miles) at the end of August. The car will be loaded as will a 4x8 uhaul which will likely weigh in at 1300lbs full. After looking into a external transmission cooler on these vehicles i was unable to find an instance of a newer rav having this addition. Whats the verdict on the necessity of a trans cooler on newer gen ravs in addition to the stock one on the vehicle already? I can see how it can help extend life of the trans, but if the stock cooler is enough on newer gen Rav4s it seems like a redundant addition that could void warranty if something broke.
 

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The only way to know for sure is to monitor tranny oil temp on a test run, and see if it rises considerably when you climb hills. On other Toyota boards folks have found the code to allow a Scan Gauge to monitor the thermocouple that's resident in the system.
 

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The only way to know for sure is to monitor tranny oil temp on a test run, and see if it rises considerably when you climb hills. On other Toyota boards folks have found the code to allow a Scan Gauge to monitor the thermocouple that's resident in the system.
Okay, I just downloaded obd fusion’s Toyota diagnostic pack and will measure the tranny temp. Max temp should be around 215 right?
 

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215' F is pretty high. At that temp Toyota WS fluid won't last all that long. 160' F or below, IIRC?? Sorry - you research and let me know please?

Glad to hear you got this far!
 

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215' F is pretty high. At that temp Toyota WS fluid won't last all that long. 160' F or below, IIRC?? Sorry - you research and let me know please?

Glad to hear you got this far!
I spoke to a Toyota technician at my local dealer, he said the temp should be between 180-215 degrees. He described that the cooler utilizes the radiator coolant to exchange heat with the transmission oil via a heat exchanger within the hockey puck cooler. He said an auxiliary cooler wouldn’t hurt anything but the car should be able to handle the loads I’m putting on it. The advice he gave was to monitor the temp and make sure the transmission doesn’t search for gears while going through the mountain passes which can be corrected with the manual gear selector.
 

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I did a little poking around and agree that my initial statement of 160' F is probably on the low side. 185 to 210 (roughly corresponding to engine coolant temps) is probably more normal. But if you find that you are regularly running at 215 or above, I'd consider abandoning the notion that the fluid is 'good for life' and consider at least doing a 2-3 quart refresh (drain and fill) after 30k miles or so. Just to be on the safe side.
 

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I agree, there’s no way I’m waiting to change that fluid and will likely do it around 60k. I recently towed a 2000lb load 5 miles on a highway with stop and go in 75 degree weather and got the trans to hover around 205. No bad considering the load I had. Only difficulty I felt the car have was braking.
 

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Driving from Las Vegas to Southern California recently in a 100F weather, monitoring of transmission fluid temperature at 215F maximum in an uphill road, and getting steady temperature of 190F while driving in a long, flat road....
 

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160 - 200 are considered normal temps providing your engine radiator is functioning properly . If your engine overheats , your transmission will also overheat

Normal fluid temperature in transmission to be 175 deg. F.

Rate of oxidation to double for each temperature increase of 20 deg F above normal (175 deg F). As oxidation rate doubles, useful life of fluid is cut in half.

At 175 deg F life is 100,000 miles
At 195 deg F (20 deg above 175) life is 50k miles
At 215 life is 25k miles
At 235 life is 12k
At 255 life is 6,250
At 275 life is 3,000
At 295 life is 1500
At 315 life is 750

At temperatures much above 300 deg F the metals in the transmission will tend to warp, twist etc. high temperatures causes the formation of varnish deposits which impair or pre vent transmission operation.

At a fluid temperature of 415 deg F fluid life is 30 minutes!

Source: Empire Lubricants Inc.
 

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I made the drive while monitoring the temps of fluid. I hit 220F on the transmission easy on some of the uphill sections of mountain passes. At one point I hit 240...Needless to say I went in to drain and fill the transmission fluid after i arrived and the fluid was pretty dark. During the drive, I experienced smoke exiting the tail pipe intermittently. Apparently the dealership that changed my oil before the trip overfilled it by ~3 quarts....This may have had a negative affect on cooling ability since more oil in the engine was needing to cool than normal, putting more load on the coolant which also takes heat from the transmission. I was towing ~1500lbs and had myself and a few bags in the car. Besides the high heat and smoke periodically, the car performed well.
 
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