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sienna xle awd cant tow?

5 messages,  Last post on May 05, 2012 at 11:31 AM

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What is this discussion about? Toyota Sienna, Toyota, Van

Messages Page 2 of 2

#4 of 5 Re: sienna xle awd cant tow? [fibber2] by ateixeira

May 04, 2012 (12:04 pm)

Replying to: fibber2 (May 04, 2012 12:01 pm)
Worst is that the shops all tighten the cover with a 1/4" drive and it's WAAAAAAAAAY overtightened. I do oil changes now.

#5 of 5 Re: sienna xle awd cant tow? [ateixeira] by wwest

May 05, 2012 (11:31 am)

Replying to: ateixeira (May 03, 2012 1:29 pm)
If you research/track the history of all these attempts to make a silk purse from a sow's ear, FWD to F/awd, you will find that they have proven to be not very reliable. Even the best of the best of these, the Acura MDX, has been fraught with problems. Pre-mature drive line component failures resulting from the heat/stress of having the front and rear drivelines AUTOMATICALLY (no driver interaction required) locked together, even partially so, regardless of roadbed traction capability.....on highly tractive surfaces.
 
There were 3 iterations of the RX300 F/awd early on, '99, 00, 01, and then finally the latest, 2010, same as the Venza. The MDX was switched to the more functionally capable SH-AWD system mid-decade but now seems to be having another spat of driveline components failures.
 
I don't at the moment know if the Sienna has of yet been switched to the newer system initially introduced in the Venza, but if not you will not have a functionally F/awd system absent the use of TC to enforce engine torque distribution to the rear. The problem is that along with TC braking of the front wheels to enforce torque distribution to the rear you also get FULL engine dethrottling simultaneously.
 
In any case the introduction of additional driveline stress/HEAT due to the towing weight to an already over-stressed system would not be advisable.
 
And there is a problem with adding oil/ATF coolers, while they can help to keep the average oil/atf operating temperature within a reasonable level they cannot alleviate localized heating of individual components within the transaxle or the PTO/PTU.
 
That was the problem with the '00 RX300 transaxles. The '99 F/awd RX300 transaxle failures were nothing less than abysmal, horrid. The quick fix (firmware) Toyota came up with for the '00 MY was to continuous maintain the ATF line pressure at a higher level. That resulted in an undue, unplanned for, localized HEATING of the gear type ATF pump and the resulting failures.
 
As of the '01 RX300 MY the VC "centric" F/awd system was abandoned in favor of TC braking to provide "last resort" (front wheelspin/slip is already present) "awd" capability. It wasn't long after that Toyota was forced to provide, due to owner outcry, a TC "off" functionality.
 
For the '01 and later F/awd RX300 models the VC fluid was reformulated so as to not be functional under any circumstance as VC functionality was a major contributor to the stress/HEAT issue.
 
Throughout the RX330, and most of the RX350 production period, Lexus marketed the RX series as if the VC was still in place (and thereby presumably functional) while in actually it was not included in the design, at least if you believed the factory repair/shop manuals.
 
As of 2010 the RX350 F/awd system was switched to the possibly more functional, pre-emptively, "before the fact", system first introduced in teh Venza and used for many years previously by the Ford Escape/Mariner/Tribute products.
 
It remains to be seen whether the correct compromise has been reached, CAN be reached, between F/awd functionality and to much stress heat due to the level of functionality.

Messages Page 2 of 2

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