Transaxle Oil Analysis

Hi Dave,

We only have a limited number of samples and some informal observations from highway driving. Near as I can tell, the only correlation that we know about is "dusty" environments -> higher silicon/aluminum contamination. In 100F weather at 70+ mph, I'm seeing MG1/MG2 temperatures climb to 100C. This is getting in the range of hot oil but not excessively so.

I have some other ideas that are associated with aeration but nothing to publish, yet. It is possible that the differential gears may be aerating the oil and this can lead to micro-dieseling effects. Higher speeds would only compound the problem. There may be nothing we can do about this but know it is one of the aging mechanisms and use testing to determine when the oil should be replaced.

Bob Wilson

 

This is a fairly easy DIY service if you have the capability to do your own work. You need 4 qts of WS ATF (I bought it for $5.20 / qt) and two aluminum washers for the drain and fill ports (about $0.80 each).

I would think you could get this done for about $50 - 75 (about 30 min labor). Maybe an independent shop if the dealer wants too much.

 

Hi Bob,
Thanks for sharing the data on your website. Good to know that higher speeds compound the problem. Yet another reason to drive slower (and get the better mileage).

I understand that air friction is proportional to the velocity squared. I wonder whether this is true for lubrication friction (being proportional to the velocity squared or linear with velocity)?

Thanks
Dave

 

In California, the Santa Cruz dealer is quoting about $200. One hour of labor plus the cost of the fluid. To drain and refill.

I asked the dealer if the pan could be dropped and wiped clean, and they want an additional 3 hours, which would then be in the $450 range.

For those who have done this service, did anyone ask for the pan to be removed and cleaned and if so what metal shaving/sludge was found?
Thanks
Dave

 

Since you own a 2G, there is no drain pan to be dropped. The magnet on the drain plug needs to be wiped off, there probably won't be much accumulation of ferrous powder on it.

You need 4 qts of Toyota ATF WS which should cost ~$20 plus two new aluminum washers which should cost $3. So if your dealer wants $200 the labor rate must be unusually high! Might be worth your while to learn to DIY.

Classic owners will find significant powder debris on the magnet and if the transaxle is in bad shape, the magnet will look like a bad hair day. I've done this transaxle oil change on both of my Prius.

 

I did this myself in less than 30 minutes including taking a sample for analysis. It requires about the same effort and skill needed to perform an engine oil change. So I think the amount your dealer quoted is way high.

Patrick is correct - there is no pan on the 2G (2004 -08). There is a magnetic drain plug. I had a lot of grey metallic (Fe) debris at 9562 miles. The ATF was still red, but much darker than new WS ATF.

 

What's the best oil to use for the transaxle? Is there an equivalent synthetic oil like Mobile 1 5w-30 for the transaxle?

Thanks
Dave

 

we're doing this at 50k for the simple reason that we have the fluid and now it's taking up space we wouldn't mind having back, as opposed to residing on a shelf in DH's work area where space wasn't an issue.

anyone collecting samples? i can't pay for an oil analysis as things stand right now, but i'll ship to anyone who really wants it.

we're currently just over 47k (um, maybe 48k, i forget) so it will probably be done next month or early may.

 

I think its probably best to stay with WS ATF for the 2004 -08 transaxle. Some of us believe that the dielectric properties of the fluid could be important as well, but there is no definitive proof one way or the other. It is probably best to use WS for warranty coverage as well.

 

I think Bob Wilson is.

 

Hi Bob,
OK, Dusty environments is bad for transaxle lubricants. Makes sense.

What about acceleration rates? If driving style involves slow acceleration and constant speed, is that easier on the transaxle lubricant, or is this a small minor effect?

I'm surprised the transaxle box is not sealed and that dust can penetrate the seals, but perhaps the dust and dirt ingress via other paths, or the seals leak due to coefficient of thermal expansion of the associated materials.

Thanks
Dave

 

The Prius transaxle has a vent plug located on the rear in a difficult location close to the firewall:
Prius Transaxle Vent

The problem is the transaxle does not incorporate a flexible, closed breather tank. This would keep the internal pressure low instead of the one-way valve that currently puts a negative pressure inside the transaxle.

Bob Wilson

 

Hi Bob,
Great photos of the vent. I believe these photos are from a 2003 model. Do you know if this is for the newer model (2005-2009) Priuses as well?
Thanks
Dave

 

I don't know but can assure you that it is an SOB to reach.

Bob Wilson

 

very interesting stuff here. I have about 9,000 mi now on my 07. Should I dump it and pour in some new ATF? Or wait to 50-60 thousand? I should still have the car then..do not know though. All this talk of metal shaving's has me worried.

 

I would consider "Vegas" to be a somewhat dusty area. I would recommend the oil change and testing closer to 30-45k miles. If you head out to dirt road often, closer to 30k. If not, 45k to even 60k miles makes sense.

Bob Wilson

 

I replaced my trans oil at 26,535 miles and 2.5 years of service. The oil was put through three Alaskan winters.

I sent the oil to Blackstone Labs for analysis and they mentioned it was time to change it. The dealer mentioned the fluid should be good for 100,000 miles.



Total Acidity Number was 1.7, so pretty acidic. This is NOT a lifetime fluid, especially the initial fill!



The magnet was lightly coated.

 

WOW!

Thanks for the info. It is seeming like 30k might be a good time to change out the initial transaxle fill.

 

I'm considering doing the transaxle oil change myself. I've been looking at Bob Wilson's photos, but I think he has a 1st generation Prius and I have a 2nd generation Prius.

I'm wondering how best to put the oil in. I presume some type of tubing to pump the oil into the side opening?

Anyone one have photos or links of this work for the 2G Prius that I can review?
Thanks
Dave

 

Hobbit has a whole page devoted to it here, but ignore all the stuff about removing the inverter. The only special equipment needed is a funnel with a long hose attached to it. There is a picture on this page showing Jesse holding the funnel.

Simplified Instructions for Transaxle Fluid Replacement:

1. Lift vehicle for access to drain and fill ports

2. Remove plastic cover over radiator for funnel access.

3. Loosen fill plug (fill port has hex head) Refer to picture(s) to avoid mistaking it for coolant port

4. Remove drain plug (drain is 10mm internal hex) and let drain

5. Replace drain plug and torque. Using a new washer is optional but a good idea for both plugs

6. Remove fill plug. Using the funnel from above with the tubing inserted into the fill port, replace the fluid. The level should be within 5 mm of the bottom of the fill port. Basically you can fill until fluid starts to run out of the port and let the fluid level be even with the bottom of the port. Car should be level to check the level of the fluid.

7. Replace fill plug and torque.

8. Replace the plastic cover over the radiator.