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?

What size is the transaxle drain plug? Just to make sure I have that socket. I will try to drain the thing to look for chunks and possibly to get it tested.

This may help:

2003 Prius - Cold Weather and Transaxle

Ask the seller for the codes. I can look them up.

If the car moves at all, see if there is speed proportional hum that does not go away if you roll in "N." That is the signature of a failed MG2, the most frequent problem.

The gears are nearly indestructible. What I'd recommend is opening the 'filler' hole and sticking a finger in to get a sample. If it smells burnt ... not good but not fatal. The real test is rolling the car in "N" and hearing the 'hum.'

Can the car move on it's own? If not sure, turn it on and off three times and see if the error lights go out. Then put it in gear and see if it moves.

Bob Wilson

The car is mobile. I think it was driven to the garage. I will see if i can do a coasting test. How fast do you need to be going to hear the hum? I'm wondering if this can be done in the parking lot.

Is there any point in checking the battery voltage. The seller claims it's fine as far as he knows. He works for the co-op that is selling it. I trust that his info is good because for that price they are just trying to cut their losses and he has no personal interest in the sale other than getting it out of his hair.

Your site is a wealth of info and fascinating. Nice work.

I think we will buy it. At $1500, we could part it out and not loose our shirts if it goes sideways.

What happens is if MG2 burns out some windings, they become a permanent, short. So as the car moves, MG2 steals energy from the rotor and being a dead short, it causes a speed dependent 'hum.' I've never heard it but a couple of transaxle failures have confirmed it as the 'kiss of death.' Needless to say, the heat builds up in the transaxle and things only go down hill.

At $1,500, it sounds like a fair price for a 'fixer upper' and if you have a nice place to work on it, a lot of fun. You may be able to figure out how to remove the transaxle w/o taking out the engine but that is going to be one heavy piece of metal. Work SAFE!

Art's Automotive mentioned having trouble getting the 'shims' to rebuild the transaxle properly. It may be better now but there is no guarantee.

We had one person in California report swapping in two salvage transaxles and having them both go bad (check the "Prius Technical Stuff" message archives.) But that was just one report.

My thinking is try 'cheap' and you might get lucky. If not, you can always get a new one from Toyota and put it in yourself.

One caution, don't ignore the 12 VDC battery. In that old of a car, they do wear out. Just be prepared. Also, you may want to try and put a 'forced charge' on the traction battery before removing the transaxle.

A forced charge is holding the brake (or leaving it in "park") and flooring the accelerator. The engine turns MG1 and puts a charge on the traction battery until it is fully charged ... then the engine shuts off by itself. This just leaves your traction battery in a nice, fully charged state. Since MG2 is not turning, it should work just fine.

Do get the Toyota manuals, often available on Ebay. Volume 2 is critical, Volume 1 has more diagnostic info.

Bob Wilson

We took a look at it and put down a deposit today. We might tow it home tomorrow if we can find a tow bar. I think your idea of permanent tow bar mounts is a good one. We can always rescue it with the van and avoid towing charges. Luckily it's just below the max tow capacity of the Previa.

I couldn't get it running but possibly because the lead acid was dead. The screen had a grey PS icon, grey battery icon and a red car icon on it. I hope the main battery revives. It was sitting for about a month. He said the only code it threw was the P3120. It was driven to the dealer for a diagnosis but when they were done with it, it wouldn't start again. He was pretty peeved at the dealer. I hope it will start if I clear the codes so I can charge the traction batt.

Thanks for your help so far. I'm sure I'll be bugging you again soon. I'll start a revival thread for it somewhere here or at Prius Chat.

Thread hijack complete, sir.

In the trunk on the right-hand side is a space that holds the 'tow eyelet.' It screws into the front and using two drivers, a rope, and keeping the speeds low, you can get it home.

Over in "Prius Technical Stuff," one of the members rigged some heavy gauge, angle-iron and a ball-hitch that bolted together for 'slow speed', limited distance towing. Check the message archives for the photos.

The 'recommended' towing practice is to put it on a flat trailer and tow the trailer. The problem with the front wheel dolly is the angle is too steep at the rear and grinding the tail pipe.

My setup is for 'dingy' towing but that is another story.

I would recommend trying the Yahoo Group, "Prius Technical Stuff." IMHO, those are the Prius 'brain trust.' PriusChat is good but sometimes a little ... noisy. Something about a text based interface that seems to 'cull the heard' if you know what I mean. <grins>

BTW, be friends to EcoModder and share your progress here. One of the things I admire are the large ratio of fact-based, experimenters. Sharing your rebuild project progress helps folks understand the Prius is different but not that different.

Bob Wilson