While looking for something else, I found: Art's Automotive - 30K Service, 2nd Generation Prius Nice write-up and though NHW20 oriented, timely today. Bob Wilson
I think the recommendation to change pink Toyota SLLC engine and inverter coolant every 30K miles is unnecessary. The 100K mile initial change interval with subsequent changes at 50K miles is fine. (If red LLC is used, then the 30K mile change interval would be justified.) When the old coolant is drained, it looks like new with no sediment, so I'm not worried about the fluid losing its anti-corrosion characteristics. I also question the concern about ATF WS, moisture, and the advice to use a closed container. This is not like brake fluid, which truly is hydrophilic (if you get a bit of brake fluid on your bare skin you can quickly tell that the brake fluid likes to absorb water.) The Toyota TSB which announced the availability of ATF WS several years ago made no mention of special handling being necessary. Ditto with the Toyota Prius repair manual.
They mentioned pH and I suspect this is a metric for a real risk factor. We've had scattered reports of jelly-like material in the coolant. Hobbit found it in coolant passages and at least one report of draining coolant with globs in the fluid. A hypothesis, I suspect if the pH is driven the 'wrong way' the coolant can leach aluminum into salts that cause the globs to form. The lubrication literature is full of references to the problem of water in oil: How Water Causes Bearing Failure I suspect engine oil changes are in part driven by the water vapor, by-product of combustion as well as the particle load from combustion products. Bob Wilson
Long term (10k mile+) UOAs on properly running engine show no more water than 3k mile UOAs. The oil gets hot enough to drive any water out of it. If you never or rarely warmed your engine up enough to get rid of the water, then you could have water contamination issues.
How do they compare to virgin oil? The reason I ask is I suspect there is a latent water level that a properly warmed up engine will maintain. However our UOAs may not be sensitive enough to detect these levels. Still, I think your point is well taken. Bob Wilson
don't know the price, but again, this is for the long term owner, and may well be worth it. i'd go along with anything patrick and bob can agree on.
Most VOAs I found either didn't report water or reported it in the form x.x%. 0.1% was the highest I saw which is 1000ppm, so didn't address the 500ppm level of concern in the article you linked to. I did find this table with some recent 0W-20 VOAs Castrol Edge 0W-20 - Bob Is The Oil Guy I was surprised at the up to 0.15% water in the VOAs using the Karl Fischer Titration method. I wonder if that level would have shown up in a conventional oil analysis because of the different methods used. I also read that even the KF method is unreliable for engine oil at levels below about 200ppm because it partially misreads some oil additives as water. That's not very relevant here though. I looked at several UOAs from 9k mile or longer changes here. Amsoil SSO 18,200 miles 1 year 08 Acura TL 3.2 - Bob Is The Oil Guy Each one I looked at reported water as 0.0%, <0.1% or negative. All essentially 0 with the measurement method used. Given that normal sump temperature on a warmed up IC automobile engine is over 200F, often well over 200F, low to no measurable water makes sense. The sump temperature is also the is the coolest oil gets in an engine without an oil cooler. Oil temperature at the top piston ring can exceed 300F, very little oil is there at any given time, but it all eventually passes by there and gets exposed to those temperatures. Oil delta-T on a trip through the main bearings would be on the order of 15-30F, oil splashed on the cylinder walls also gets a temperature boost. The PCV system is continually removing gases from the crankcase, so water vapor would get drawn out by the PCV system as it was created. I would actually expect the 0W-20 oil with the 0.15% water VOA to become significantly drier after a good run at normal IC operating temperatures. :focus: What does concern me though is the alleged (I think it is real to some extent) hygroscopic nature of the WS transmission oil. Based on the MSDS sheet, the basic oil in WS in the nothing special and isn't hygroscopic. If the oil is hygroscopic, it must be because of some additive or other part of the formulation, perhaps some ester? Does anyone have a reliable source of information that WS is actually hygroscopic (or hydrophilic). So far I have read a lot of unsubstantiated comments on the web and mention of a TSB but have seen no copies of the TSB. FWIW, my August 2009 edition of the Prius service manual doesn't mention taking any special care when putting WS fluid in the trans-axle. That is not to say there might not have been a later TSB.
Ask, and ye shall receive... Also, take a look at the back label on a container of brake fluid and you will see a warning about only using fresh fluid from a sealed container, etc. Look at the label on a bottle of Toyota ATF WS, and you will see no such warning.
It's not an issue. The single article cited concerns plant machinery, not internal-combustion engines. They aren't, and haven't been since the 1950s.
Thanks Patrick, those TSBs can be hard to find. I did find an indication that there is a later version of that TSB though, a TC006-03R. I found several reference to it but no actual TSB or significant quotes. Do you have a source for such things?
Are you saying there have been no globs, or are you saying they don't matter? If you are saying they don't matter how did you come to that conclusion. The immediate topic being discussed was transmissions, not IC engines. Since automotive transmission often have higher strength and harder gears in them than industrial machinery and metatallurgically identical or similar rolling element bearing materials, please explain how hydrogen embrittlement because of the presence of water wouldn't be a problem in an automotive transmission when it is in plant machinery. Please use short simple words so this dumb old mechanical engineer can understand you. I have had some actual experience with the results of hydrogen embrittlement because of design, manufacturing and maintenance problems in high strength steel in automotive components so you won't have to drop it completely down to a kindergarten level.
Neither. I am saying that coagulated coolant is not a common issue in the Gen I Prius inverter cooling system. Someone bought an inverter on eBay, with no knowledge of how long it had been sitting or its service history, and found such material in the coolant passages. But one example does not make a statistic; it is rare for an inverter to fail in the field as a result of clogged coolant passages. Keep in mind that some coolants on the market have a reputation for gelling. Such coolants are not recommended for use in Toyota's inverter cooling systems. The post to which I responded had specifically referenced engine oil changes. Here is the quote: Here is a portion of your response: It appears to me that engine oil as well as transmission fluid was being discussed. I didn't say that it wouldn't. Again, I was responding to someone who had specifically referenced engine oil changes. Based on your comments within this thread, however, I wonder if a more relevant question for you to ask would be "is hydrogen embrittlement, caused by the presence of water, a problem in a Prius transmission that uses WS fluid?" If so, the short answer to that question would be no. Gear failure is not common in either the Gen I or Gen II transaxle. Bearing failure is even more rare. It's as simple as that.
I asked them for a quote and the total was $605 out-the-door. Seems reasonable for all of the work that they are doing.
