Transaxle Oil Analysis

[etyler88]

Originally Posted by hobbit

.
If you had positive pressure, have a close look at your half-
shaft seals...
.
_H*

Thats what she said

[dryismyquest]

Originally Posted by Patrick Wong

When the Prius has been driven for a while and the transaxle is fully warmed up, I do not believe that any significant pressure difference exists inside vs. outside the transaxle case. The partial vacuum inside the case develops after the transaxle cools down.

When the transaxle is cold and the fluid is changed, I have noticed that leaving the fill plug installed while draining causes a mess just because of the glug glug that the drained fluid makes since air has to enter the drain hole while fluid is exiting the same hole. Hence I remove the fill plug, let the pressure equalize, then the drained fluid comes out in a predictable and controllable manner.

As Bob and Hobbit indicated, it would be a first to find a situation where there was higher pressure inside the transaxle. In that case, one would expect to see fluid seeping out at the axleshaft seals.

Regarding your first paragraph, the car had been driven for a good 1/2 hour - 45 mins. prior to my removal of the drain plug. I would say I removed the drain plug no more than 10 minutes from the time the engine shut off, so the fluid was pretty darn hot too.

I'm not saying there was a "higher" pressure inside the transaxle, well, I suppose technically, by definition, anything greater than a specific value of negative IS higher. I'm not exactly a fluid dynamics major, but, if you have a situation where there's some amount of negative pressure, fluid, and a drain hole involved, if air were to suddenly rush in, I would imagine the fluid would need to be displaced to some degree, or at least disturbed? I mean, after all, I did hear, for a brief moment, a "hissing" noise.

I just know that's the way it happened. No fluid appears to be seeping out anywhere externally.

I think I just happened to loosen the drain plug a bit too quick, such that gravity, and that little bit of negative pressure did their work spectacularly well.

[Patrick Wong]

Originally Posted by dryismyquest

...I think I just happened to loosen the drain plug a bit too quick, such that gravity, and that little bit of negative pressure did their work spectacularly well.

Thanks for the update. I was just wondering what the used fluid looked like and how many miles you had on it.

[bwilson4web]

Originally Posted by dryismyquest

Regarding your first paragraph, the car had been driven for a good 1/2 hour - 45 mins. prior to my removal of the drain plug. I would say I removed the drain plug no more than 10 minutes from the time the engine shut off, so the fluid was pretty darn hot too.

Uh OH!

Originally Posted by dryismyquest

. . . I'm not saying there was a "higher" pressure inside the transaxle, well, I suppose technically, by definition, anything greater than a specific value of negative IS higher. I'm not exactly a fluid dynamics major, but, if you have a situation where there's some amount of negative pressure, fluid, and a drain hole involved, if air were to suddenly rush in, I would imagine the fluid would need to be displaced to some degree, or at least disturbed? I mean, after all, I did hear, for a brief moment, a "hissing" noise.

The cool shop air entered the hot transaxle and helped cool things off by 'expanding'. It then jetted the remaining oil out and shot the drain plug. Amazing, I hadn't considered changing the oil while the transaxle is hot:




This is the type of experiment that Mythbusters might enjoy ... with proper, hot oil resistant clothing and head gear.

Bob Wilson

[dryismyquest]

Originally Posted by bwilson4web

The cool shop air entered the hot transaxle and helped cool things off by 'expanding'. It then jetted the remain oil out and shot the drain plug. Amazing, I hadn't considered changing the oil while the transaxle is hot:
This is the type of experiment that Mythbusters might enjoy ... with proper, hot oil resistant clothing and head gear.

Bob Wilson

Edit, hey, wait a minute, then why doesn't this really happen with the oil? I guess there's more "space" and less of a vacuum???

[dryismyquest]

Originally Posted by Patrick Wong

Thanks for the update. I was just wondering what the used fluid looked like and how many miles you had on it.

Uh, well, I WAS hoping to get a sample... It appeared black. Maybe it was sooo deep red it appeared black? I don't know, but it looked, to me anyways, no different than used motor oil. Of course, my garage lighting isn't that great, and it was at night... Car has about 87,000 miles on it.

[whodat]

2006 Prius 65K transaxle oil analysis high in iron and aluminum and silicon. Report is attached. Based on this, the transaxle oil may not be good to 120K miles as suggested by Toyota.

[whodat]

2006 Prius 65K transaxle oil analysis high in iron and aluminum and silicon. Report is attached. Based on this, the transaxle oil may not be good to 120K miles as suggested by Toyota. Attached file is in jpeg format.

[whodat]

2006 Prius 65K transaxle oil analysis high in iron and aluminum and silicon. Based on this, the transaxle oil may not be good to 120K miles as suggested by Toyota. Blackstone Oil report highlights below:

"Aluminum and iron were on the high side in this sample, but neigher were high enough to suggest any serious mechanical problems are developing in this Prius transaxle. Universal averages show typical wear from this type of system after about 29,000 miles use on this oil. If this oil was run longer, that likely explains the higher wear. The oil was normal in viscoisty for an ATF, though insolubles were at the limits. This along with the higher wear is a good sign that the oil should be changed out if you haven't done so already. Theck back in 25,000-30,000 miles to monitor."

Aluminum 101 (universal ave 60)
Iron 219 (universal ave 155)
Silicon 188 (universal ave 173

All other parameter at or lower than univeral averages.

Sorry about the multiple postings, I was unable to upload a legible pdf or jpeg file.

[Patrick Wong]

I've attached a copy of my 2004's used transaxle fluid analysis, taken at 32,755 miles back in July 2007.

Al: 79 ppm
Fe: 205 ppm
Si: 198 ppm

Note fluid viscosity at 100 degrees C was 4.7 cSt compared to new fluid at 5.5 cSt, a 15% decline. Bob Wilson previously had new ATF WS fluid tested and made those results available.

Based upon these results, I decided it was a good idea to change my transaxle fluid at 30K mile intervals in the future.