Inverter coolant pump
 

Hi,

We've seen two, possibly three inverters in the older NHW11s that appeared to lose their 12 V DC-to-DC converter. It also seems to correspond with inverter pump failure. Funny coincidence.

Regardless, Hobbit analyzed Prius inverter coolant pumps and found both the NHW11 and NHW20 use a single bearing mounted shaft. In contrast, the 2010 (ZVW30) has a redesigned, dual-bearing shaft, three speed pump, part G904048020. I've found them new at Champion Toyota for ~$160 and am trying to get one from a salvage. I've also ordered the electrical schematics manual to join Vol. 2.

The other night I went out to 'listen' to my pump and though I could barely hear it, I was able to verify turbulence in the reservoir. With 130,000 miles, I'm thinking replace the inverter pump before failure rather than risk an inverter failure.

More about this as details emerge.

Bob Wilson

Didn't hobbit also do some testing that showed inverter coolant temps rarely get high enough to do damage to the inverter?

If so, I hadn't seen it but then he is admirably prolific.

I had been under the impression that an inverter pump failure would reveal itself by throwing an inverter temperature code. But now I'm not so sure based upon a North Carolina and Oregon report. Plus, I'm living through 100F (35C) days in Alabama. This is compounded by a specific failure mode in the NHW11 of the 12V DC-to-DC converter.

It looks like the 12 V DC-to-DC converter in the NHW11 assembly is located at the bottom of housing. But I don't have any more details such as coolant flows adjacent to that part. There have been at least two Prius whose DC-to-DC converter failed yet they could drive . . . their drive electronics are still working.

I don't know how far I'll get. If I can get a salvage, 2010 inverter pump for under $100, I'll probably 'do the the experiment.' Then we'll know if the mechanically sounder, 2010 inverter pump will work. But I was seriously surprised to find I could barely hear my current pump even with the hood up.

Bob Wilson

I think this is the part that went out on our NHW20 Prius. Around 105,000 miles, my wife was in Wisconsin, when the pump that cools the electronics side of the house went out. She was advised by the Toyota dealer that she could drive it, but take it slow. It wouldn't go over 25mph, so it took a while to get to the dealer... They said "This never happens." but conveniently had 3 of the pumps in stock, and could do the work same day. I don't know how typical this really is, but I am guessing the swap wouldn't hurt, and could save you from being stranded sometime (and keep you from paying dealer rates on parts and labor).
Our car was driven "like other people drive" for the first 95,000 miles of it's life (before we got it), so I would expect your components to last longer... just how much longer?

Most of the pumps seem to fail (at least on the 2nd gens) around 100k miles. It doesn't matter how you drive it. That pump is on as soon as you power the car up until you turn the car off. It just runs and runs. The nice thing is that if you catch it early, its a very easy fix.

You have a water cooled inverter? Does it use engine coolant, or is there a seperate, lower-temperature circuit?

Honda uses air cooled inverters with an enormous heatsink (54 fins, 30cm * 5cm) and a large blower. The housing gets a bit warm when I'm operating in charge depleting mode, but I've never heard the blower kick on.

Btw, I've never heard of a Honda DC/DC or inverter failing.

Thanks, Daox, any other "heads ups" I should be aware of? So far that is the only thing mechanically that has needed done (other than changing oil, rotating tires, etc). I figure with some heads up, I could learn about it in advance and do the work on my own.

Yep, its a seperate loop just for the inverter.



There is also the 12V lead acid battery that tends to fail after ~5 years. Not horrible life, but not amazing life either. I check my battery every once in a while with the SG before I power up the car. I know mine needs replacing before winter. I believe its still original. The standing voltage is just over 12V I believe which is fairly low for a 12V battery and below spec according to my bentley manual.

Hey Wyatt,

You may want to have the transaxle oil changed. We're finding the NHW20 transaxle oil seems to last about 60,000 miles but many folks don't know to change it. It is a fairly simple process and Hobbit has documented it. But you may want to have a spare, dry, water bottle to take a sample of the oil. If you have a sample, you can choose to test it. If you don't have a sample container, testing later is no longer an option. <grins>

FYI, it is time for my NHW11 transaxle oil change.

Bob Wilson

Interesting, I think we just crossed 115,000 miles, so the transaxle oil change would be a good idea... Are you proposing that we have a transaxle oil change date? Do both at the same time? I would be up for it!