Gen 1/Gen X Inverter coolant pump - a preventive maintenance item?

My '03 Prius (265k miles) just last week threw the P3025 and P3030 codes, on a not particularly hot summer day in the American northeast... which I presume is the inverter coolant pump. While disassembling most of the front end to get the left headlight out (there was some, ummm, mechanical deformation as well as rust to contend with), and waiting for the replacement part to arrive (my local Toyota dealer says the closest ones are Manhattan and Ohio) I was thinking... here's a critical item in the hybrid scheme, would it make sense to replace the pump as a preventive maintenance (PM) item, and if so, at what interval? Which led to... Toyota missed a great opportunity to log (a) engine on-time (running hours) and (b) inverter operating time (running hours) somewhere in their OBDII data.

So, I estimated. Assuming an average speed of 30 MPH, a failure at 265k miles is about 8800 hours. Hard drive MTBF (Meant Time Between Failure; for statistical types, Weibull B50) is 10k hours. So, it is about now ripe for a failure.

Risk analysis: Now, a Gen I inverter assembly is about US$3k (new, retail) plus installation, so lets call it US$4k. The pump costs US$160 (Toyota price; others may find lower numbers) plus US$240 for installation labour, total US$400. It's about 10% of the price of the inverter that it's protecting. Plus the pain-in-the-posterior of being car-less (inconvenience) while someone hunts up a replacement inverter assembly.

So I posit that the risk-reward is pretty good for making a preventive replacement of the inverter pump at about 200k miles ( 320k km). A life expectancy of 200k miles is about 6700 hours... so if the B50 is 10k hours, I'm mentally thinking that the B10 (10% failure point, or one-in-10 chance of a failure before or at this point) is around 200k miles.

I suspect that, since the pump failure mode appears to be bearing-related, not much has changed in the last 15 years, so the analysis may hold for other Prii of newer generation, but similar mileage.

(There is, of course, the opportunity for manufacturing or design screw-ups... the Gen II Prius Inverter Pump TSB and replacement campaign is testament to that eventuality).

Comments? Particularly from engineering / failure analysis / statistical types?

 

The Gen IIs had an inverter pump manufacturing problem, and a bunch of their pumps died prematurely. Hence the comment about their special "inverter coolant pump campaign" in many of the comments in that thread. So the Gen II case is 'special' in that regard.
As importantly, I would like to start a list of "gee, I never thought of that" PM items which should be replaced on elderly Prii.
For Gen I (and probably all Gen N>1) , I have, for the 200k miles mark:
--maintenance operation on the AC magnetic clutch (clean the clutch faces)
--replacement of the water pump and drive belt
--and now this inverter pump.
By age, the coolant (both engine and inverter) & ATF fluid should be done every 5 years.
Plugs every 100k miles
...Time flies, when you're having fun...

 

Replaced the Gen I inverter pump this morning. Part #G9020-47022, about US$115 (part + s/h) from
Toyotaparts.mcgeorgetoyota.com (formerly ToyotaOnlineParts.com). Had the bumper and left headlight removed previously. Part went in smoothly; the hose clamps are a pain-in-the-posterior so I replaced the spring clamps with screw-type hose clamps (much easier!), cleared the fault codes (necessary!), and began the burp-the-system process. I did NOT drain the entire coolant system; I just pulled the pump and replaced it, trying to catch as much of the coolant from the hoses as possible. I ended up losing about 300 ml (about 10 ounces). DO remember to plug in the electrical connection to the pump [after cursing the hose clamps, I forgot that...].

This car gets driven in the US NorthEast winters, so there is a fair bit of rust on the hardware. Broken bolts (requiring a drill-out and re-tap) are not uncommon.

The failure mode. I suspect that the pump bearing wears (I estimate this one operated 8800 hours), and at some point the increasing friction of the bearing reduces the pump capacity, and the pump can't pass enough fluid to adequately cool the inverter under thermal load (like, summer driving). It's possible that there is enough cooling capacity in the system that a marginal pump may persist for quite some time without throwing the fault code (which is apparently set by thermal sensors in the inverter cooling system). So a way to predict (or diagnose) a marginal pump is to monitor the inverter temperature. Since it throws a fault code, the Prius computer already does that monitoring... so seeing how close the inverter temperature is to the "declare a fault" threshhold gives some insight into the pump health. Yes, it will clearly depend on what kind of driving, outside temperature, etc. Next project is to hook up ScanGauge and see if those values can be extracted... unless someone else has already done that.

Meanwhile, since I support more than one Prius of this vintage, I have ordered a second inverter cooling pump and plan on replacing the mate's inverter cooling pump (a) as a preventive maintenance item (since that Prius is of comparable mileage) and (b) after making some before-and-after tests to see if the new pump makes a difference in inverter cooling performance... and see if the inverter temperature delta (before vs after) makes for a reasonable predictor of pump life. That assumes that the pump on Prius #2 had not already been replaced... it may in fact be a perfectly good pump. But I choose not to wait for an abrupt failure. Run-to-failure is not an option. There is no warning for this failure. And a pump failure could be catastrophic.