Transaxle oil testing results
 

BACKGROUND

The NHW11 Prius (2001-03) uses a different transaxle oil, Type T-IV, than the newest Prius that uses the Type WS. Type T-IV has viscosity characteristics similar to Amsoil ATF so it a natural to try it as a substitute for Type T-IV. Unfortunately, I didn't learn until later that Amsoil ATF has history attacking 'yellow metal' like bushing style bearings.

Testing of high mileage, used NHW11 oil revealed it wears down to viscosity ranges closer to Type WS. So rather than wear down Type T-IV, I decided to test Type WS and bypass the wear pattern.

RESULTS

The data suggests my NHW11 high Cu problem started with the Amsoil. Look at the rates:
[table="|"]Cu ppm/1k mi|sample
1.41 | 53k original Type T-IV
4.0 | 7k Amsoil
4.9 | 27k Amsoil
4.9 | 8k Type WS in NHW11 after Amsoil
2.7 | 27k Type WS in NHW11
... | ...
3.0 | 2k Type WS in NHW11 CA
2.0 | 325k Type T-IV Jesse
1.8 | 27k Type WS in NHW11 UT
1.5 | 44k Type T-IV [/table].
I'm still not ready to go back to Type T-IV because of the high starting viscosity. At this point a higher viscosity would likely put more stress on the bushings and remove the boron nitride on the surface. But it is obvious that going with Type WS has reduced the rate. It isn't as low as some of the others but I blame my Amsoil ATF test on the continued problem.

I did a hill roll-down test between the 53k oil and Amsoil ATF and there was a distinct reduction in rolling drag. But hindsight suggests it was the higher particulate load more than anything else.

Since we now have a ZVW30 (2010) Prius, I changed and tested the transaxle oil at 5k miles including a microscopic examination. We found wear material as would be expected with the initial change but also found a rate of viscosity loss suggesting that 15k miles may be when it wears out at a 15% loss. It will take a year before I change it again to see what the wear rate is after flushing the initial transaxle oil.

Bob Wilson

Hi Bob - glad to hear about the performance improvement in the new oil (even if it may only be due to the lack of contamination).

Darin

Most of us fully realize the importance of engine lubrication and it certainly has a rough environment. But many don't think about the transmission and differential as another place where quality lubrication plays role. It doesn't need to be replaced as frequently but it needs to be checked and replaced if nothing else for lower rolling resistance.

Bob Wilson

Hi Bob,

I'm looking at getting a cheap Prius that's throwing a transaxle fail code. It's got 180,000km on it and they are asking $2500. It's a 2003 sedan from a car sharing co-op. I see you were helping out on Prius chat with the guy who replaced his tranny. I looked at that job and thought this was within my skill set.

What's your 2 cents?

Thanks.

If this will be a 'project' car, not one critical for transportation, it could be a lot of fun. But if you already have a project car or it needs to be reliable transportation, I'd take a deep breath.

Before tacking the project, get Volume 2 and possibly Volume 1 of the NHW11 (2001-2003) maintenance manual. To replace the transaxle will require removing the engine and transaxle assembly ... pretty hefty weight. Then you'll need a place to work on it and find either a replacement tranny or try to rebuild it yourself. Art's Automtive has a write-up on rebuilding a tranny and it is not for the faint of heart. Still, it can be done.

Before cracking the tranny, I'd want to know the 'codes' and have instrumentation to read out the codes. If you can find a Graham miniscanner, you'll have enough. But ordinary scanners are lame about reading the other control computers. The ones that do tend to cost nearly as much as the car.

I would probably start by confirming the diagnosis but that is a little involved. I would suggest visiting the Yahoo Group, "Prius Technical Stuff." That is where my cohorts hang and they are mostly quiet unless someone brings a good problem. Replacing a 2003 tranny qualifies as a 'good problem.' If you visit the site, wander through the photos and files. Also search the message history.

Bob Wilson

Is the assembly similar to the genII in that the tranny can be extracted like the thread at priuschat? He got his out without dropping the motor. Or is it a different animal all together?

I found a used tranny locally. They want $1200 for it though. I would try to chisel that down before I bite.

Im pretty good with the wrenches but not into a rebuild.

I was surprised he was able to get it out of the NHW20 without removing both and he didn't offer a lot of details about that bit. I know Art's removed the whole assembly and that is what the Toyota manuals recommend.

Bob Wilson

What is the approximate street value for a decent genI. This one has about 100,000 mi.

There are two answers:

• Kelly Blue Book - a reasonable starting place
• Ebay completed sales - the 'gold' standard

I found my 2003, NHW11 on Ebay and was going by the Kelly price. When I found one in Texas for $1,000 under Kelly, I made the deal. I still drive the 03 Prius to and from work and use my wife's 2010 for errands in the evening. The hatchback is better for hauling groceries and 'stuff.'

Bob Wilson

Sorry to hyjack your thread and thanks for the advice.

I just talked them down to $1500. I'm going into town to look at it tomorrow or Wednesday. Kelly said about 7500 - 8500 for a fair condition private sale. The only things wrong with it seem to be the code and as a ex rental it will be a bit scuffed and dented but like Christ, I think utility is more important.

This is going to seem thick but how do you find completed sales on ebay? Do you have to follow them till they end?