Transaxle Oil Analysis

[bwilson4web]

Originally Posted by apriusfan

I just got around to checking my gas receipts for the fillup after the transaxle fluid was replaced - I gained 2 mpgs. Now the gain could be explained by the ICE continuing to break-in; but, I am intrigued about possible drag from particles in the transaxle fluid. Could you elaborate on what you have learned about drag and the early accumulation of 3-7 micron particles?

My first clue came from articles:
http://www.practicingoilanalysis.com...up=OilAnalysis
http://www.practicingoilanalysis.com...group=PowerGen

My investigation of transaxle lubrication has been going on for two years:
http://hiwaay.net/~bzwilson/prius/pri_T_cold.html
http://hiwaay.net/~bzwilson/prius/pri_tt.html
http://hiwaay.net/~bzwilson/prius/pri_toil.html

It was inspired by two key reports:
ORNL/TM-2004/247 - UT Battelle Report on transaxle performance
INL/CON-05-00964 - "Hybrid Electric Vehicle Testing"

In the "INL/CON-05-00964" report, the page titled "Fleet Testing Monthly MPG" shows that both Prius started out with higher mileage that decreased and never recovered later. One hypothesis is some combination of problems, not yet diagnosed, are causing Prius performance to decrease in service.

What "ORNL/TM-2004/247" showed is the lubricant can make a significant impact on vehicle drag. This report shows the temperature correlation, which maps to viscosity. However, they didn't look at particulates in the oil.

This is where some of the transaxle oil analysis are eye opening. The particle loads, especially in the 3-7 micro range, are impressive in a bad way. Yet there is no mechanism except for oil change, to get rid of these particles. So I've become more interested in investigating this area.

Bob Wilson

[apriusfan]

I have to admit that I am learning new things about the Prius. I certainly would not have expected to have an acidic sample after only 5,000 miles on a 'lifetime' fluid. Which makes me very curious about the results of my next sample at 7,000 miles on the odometer.

[apriusfan]

Originally Posted by bwilson4web

This is where some of the transaxle oil analysis are eye opening. The particle loads, especially in the 3-7 micro range, are impressive in a bad way. Yet there is no mechanism except for oil change, to get rid of these particles. So I've become more interested in investigating this area.

Eye opening seems to be something of an understatement.... I am waiting with great anticipation to learn what my next sample results will show. Interesting, interesting, interesting.

[bwilson4web]

Originally Posted by apriusfan

I have to admit that I am learning new things about the Prius. I certainly would not have expected to have an acidic sample after only 5,000 miles on a 'lifetime' fluid. Which makes me very curious about the results of my next sample at 7,000 miles on the odometer.

There is a mechanism related to aeration for 'dieseling' the transaxle oil. Apparently small bubbles can be compressed between gear teeth and the high pressure, gas compression heat ignites the small bubbles. But there is no mechanism for exhausting the products and in particular, small particulate carbon . . . diesel 'smoke.' The other by-products accumulate and over time, the acid level increases.

Near as I can tell, the differential gears are half immersed in transaxle oil. Furthermore, oil is sprayed about and obviously the film will get between the various gear teeth. It is another area I'm curious about and have started looking at by getting acid/base testing on selected samples.

Bob Wilson

[apriusfan]

Originally Posted by bwilson4web

There is a mechanism related to aeration for 'dieseling' the transaxle oil. Apparently small bubbles can be compressed between gear teeth and the high pressure, gas compression heat ignites the small bubbles. But there is no mechanism for exhausting the products and in particular, small particulate carbon . . . diesel 'smoke.' The other by-products accumulate and over time, the acid level increases.

Interesting concept. The pressure of the gear teeth on the oil molecules could in fact create a 'dieseling' scenario.

Originally Posted by bwilson4web

...It is another area I'm curious about and have started looking at by getting acid/base testing on selected samples.

I definitely will get the TAN test done again at the 7,000 odometer reading. Stay tuned. Only 1,000 miles to go until 7,000.

[DGH]

I have a 30K sample to be tested, is the "standard" Blackstone test sufficient?

Thanks...Dan.

[bwilson4web]

Hi,

Normally we like to see the viscosity at 40C, 100C and the viscosity index. These three numbers give us a good idea of oils ability to lubricate the transaxle. I have been using PdMA because with the additional oil viscosity test it costs only $20.

It is important to note age of vehicle and total miles as well as the 30k miles oil service upon change.

Thanks,
Bob Wilson

[KTPhil]

Any recommendation for where to have it tested? What do I ask for?
(I'm on the west coast, if that matters)

[bwilson4web]

Originally Posted by KTPhil

Any recommendation for where to have it tested? What do I ask for?
(I'm on the west coast, if that matters)

I use PdMA but there are others that can do a good job. Nora corporation comes to mind. Just contact them first and get the price of a basic oil test and 40C/100C viscosity and oil index.

GOOD LUCK!
Bob Wilson

[whodat]

Very interesting thread and data from bwilson4web.

Does anyone know how the transaxle oil breakdown changes with frequency of cold starts versus continous freeway driving?

Does continous freeway driving (presumably at an elevated temperature) break down the transaxle oil lubrication properties faster than more frequent temperature changes in the oil with short frequent trips?

I'm at 60K miles and my commute is 100 miles roundtrip. From data presented it would seem that doing a transaxle oil change soon would be a good idea. However, its an expensive service item.

Thanks
Dave