Thinking of trying a 5w40 Oil

It is your car.

http://www.toyota.com/t3Portal/document/om/OM47509U/pdf/9.pdf
Page 4 of the PDF, page 314 of the manual

SAE 5W−30 is the only oil Toyota ever recommends at any temperature.

 

Outside the US this isn't the case though. One of the members from Ireland stated that his Toyota dealer had always used 10W40 in their Prius and there were no adverse effects (the user however is now doing his own oil changes and uses 5W30).

My 2005 Prius handbook specifies a range of oil viscosities depending on the minimum temperatures encountered. However 5W30 covers the widest temperature range.

I don't see any harm in the OP trying a 5W40 (or even a 10W40) over summer, especially on an engine with so many miles on it. Cooker, if you do give this a try could you please try to document any MPG changes that you observe. I'm sure several people would be interested in the results.

 

I think the only downside will be a slight decrease in FE.

why do some on here say 5w30 is the only choice, I just put in 0w20 in my 2004, did I make a mistake?? I'm in Michigan so no hot dessert driving.

 

I did not say it was the only choice. I started by saying it was his car. I showed that it is the only grade mentioned in the 2005 manual, which Uart pointed out was the US manual. Other manuals my list other grades.

It is a 2005, it is not like you can use the 'what about the warranty?' card, he has no warranty. 5w-40 will be cheaper than an engine rebuild, which is the 'right' answer.

 

If you have such a document, please post it.

There is a TMS USA TSB which allows use of 5W-20 in certain Toyota engines previously spec'd for 5W-30 but Prius was specifically excluded from that list. As far as I know, 5W-30 remains the only viscosity approved by TMS USA for Classic and 2G Prius engines. It is true that other Toyota distributors elsewhere in the world may have approved a wider oil viscosity range.

Use of 5W-40 in the summer should be OK but you may notice reduced fuel economy. That heavier viscosity in the winter may cause engine no-start issues.

 

Some people have had good luck on the oil consumption side with an additive like Lucasoils HD or Synthetic Oil Stabilizers. You can get the same effect by adding that to 5W30, plus get whatever magic they have added to the container.

How much time do you spend at 1 bar on the battery gauge? If the engine is weak, SoC can fall all the way to 30% under certain conditions. That will kill it quick.

 

On my 2005 with 234k miles on it the engine has a bit of a piston slap.

Are you sure about your diagnosis? Piston slap or possibly lifter ticking? Have you done a valve clearance check?
I did one on my engine, found slight over clearanced exhaust valves, and after rounding the allen head plug which accesses the cam chain tensioner, decided to just leave it unchanged for a while. Just throwing an alternative out here , am still curious what other high mileage prius valve clearances are.

 

The way I've heard it explained is that the Prius will detect slow cranking and throw a code (and fail to start). It does this to protect itself, since the "starter motor" in the prius is about 10 times more powerful than that of an ordinary car. So it's to protect itself if something is seized.

It wont happen unless you combine both an overly thick oil AND extremely low temperatures. At summer temperatures it's not going to happen, not even with 20W50 oil (not that I recommend this btw).

For example, at 50F a 5W40 oil is VERY much thinner than is a 0W20 oil at 20F.

 

Save stop-leak (and even this is debatable), there is NOTHING you can pour into a car to fix a mechanical problem. You're only masking a problem until it becomes bigger.

If you're hearing a metal-on-metal noise, you better fix whatever's clanging together, until you experience catastrophic failure. Your choice, small repair now, or major replacement later.

 

There's a guy over at bitog asking a similar question. If I was you cooker I'd watch that thread and go with whatever this guy goes with. j/k

Suggestion for Xw40 oil for my gasser? - Bob Is The Oil Guy

 

I live in Lahore- Pakistan, and drive a 2007 Gen 2 with 200,000 KM( 124 K Miles) on the clock, where the summers are long and hot. The temps here peak at100 F for months. In winters the temps rarely fall to the freezing point. I have recently switched to 20 w 50 (Zic Hiflo) from 10 W 40 Mobil- Driven 3000 KM with no issues so far and with a bit of carefully driving I am getting 50+ miles to a US gallon ( yes I did my math right one reason for getting good mileage could be the temps that now a days are moderate I'm neither using Aircon nor heating

 

Any updates on 0w40?

 

Thanks for the input on your engine oil choice switch. You appear to be operating your Gen 2 in a hot climate zone. I would suggest using your AC regularly in hot weather, as this will be directly contributing to the cooling of your HV battery and will prolong its operational life.

Gen 2 Prii operating in very hot conditions have been known to suffer premature traction battery failure. Using your AC more regularly will reduce this factor. Also, unlike ordinarily ICE vehicles, the AC on a Prius will not cost you as many MPGs, especially if prudently configured to run.

The correspondingly MPG trade off is worth the long term extra cooling protection of the HV traction battery, methinks.


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