Prius Prime cylinder wash-down potential issue

I don't know if this is related to the topic of this thread: I use my Phev 90% of the time in electric, so the ICE engine may stay off for as long as two-three months. When it starts again it runs very rough for 4-5 seconds. I told the mechanic at the dealer and he suggested that a very small amount of oil remains at the cylinders walls....so he suggested to run it every now and then.
My question is: if we assume that the start is the critical phase, wouldn't "starting it every now and then" just make things worse?

 

Possibly, in the sense of increasing total amount of wear. But it might reduce the number of rough starts, which is what you were complaining about.

I think you're probably onto a loser here of trying to guess what the best thing to do is. Toyota will have actually done real-life analysis, which will beat our intuition and guesses. I think you just have to trust that their engine management will be as reasonably conservative as everything they do, and that it starts the engine enough.

No personal experience here - I doubt I've ever gone more than 3 weeks without starting the engine - there's a fairly regular bi-weekly trip beyond EV range. Never noticed any particular issues.

 

So far ICE has never automatically started without the traction battery being depleted, so, limited to my experience, no strategy seems to be implemented to prevent any wear.

 

My recollection was that it did have a function to run the engine periodically, but it was set out at the 6 month range. But I can't find a reference for that now.

Only thing I can find in the manual is a note on refuelling sufficiently:

 

That recommendation on refuelling would imply to score at least 20 l/year * 15 km/l = 300 km/year, which I manage to do regularly, the only difference is that I do it concentrated in my holidays (1 month in the summer). So I don't think I'm within specs.

I hope you are right and I'm over worried, but the that noise and vibration really scared me.

 

How so? The fuel-use-over-12-month spec (user instructions) is separate from how-often-to-start-the-engine (managed by the car, I believe).

BTW, found this older thread discussing the same issues in G4:

Can gas go stale in the 2020 Prius Prime hybrid plugin? | PriusChat

 

Well striclty speaking you are right, but i suspect that that recommendation is to be intended as a "distributed" minimum consumption.

 

Why? It's unrelated to how often the engine starts. It's just about fuel going stale.

They are so specific about "total over a 12 month period" that they make a special effort to restate it like that - rather than something more evened out like "5 L every 3 months", which they could have said if they wanted something distributed.

I can only infer that they don't want fuel to go older than 12 months - so make sure you've put in enough new fuel in a 12-month period that you don't have just 12-month-old fuel.

I guess if you do do it all in summer, you are pushing towards that limit, with 11-month old fuel, but you're still under it.

And if you refuel after 11 months before you start using fuel again, so you don't actually use that 11-month-old fuel, that would avoid most of the potential issue.

 

Must say though, it's a bit different here.

I can go a whole week without the engine ever stopping in EV mode, with the temperature below -10°C. The ability to not run the engine for 11 months is a bit fantastical

 

We don't know exactly why it is running rough. Maybe using a higher viscosity oil will result if thicker layer of oil left by the time you use the engine, if that is the cause. Or perhaps there are deposits in the injection system left by evaporated fuel, or even just air bubbles from that.

 

My 213k mile Prius C that was used in LA traffic as a commuter for the first 138 k miles doesn't use a drop of oil between 5k mile changes and the oil is barely discolored. at over 12 years age, almost clean enough to sell it for new (not that I would). The symptoms described by the OP are going to oil contaminate almost any engine going back to my 1976 280Z. If you started it cold repeatedly and did not actually drive any distance it would foul out the plugs and there was nothing wrong with the engine.
In extreme cases I would smell the customer's dipstick and if it smelled of gas, I would light it on fire with a butane lighter and show the customer why they needed to not drive it that way or they would wreck a perfectly good engine. That's a 50 year old fuel injected car, doing exactly what is described by the OP.
I also had a 1937 Ford that you could crank with the ignition off. With the cracking speed at 100 RPM (6 volt system) it would get 60 PSI oil pressure within 2 seconds of cranking time. I pre primed the oil doing just that to keep it from starting without pressure and it had NO oil filter, a slinger for a real seal, and a tube that blew crankcase fumes out into the atmosphere.
I think that the issue is non existent unless you drive the car PERFECTLY WRONG and never allow it to warm up.
Modern hybrids are trading high operating engine temperatures for efficiency,
When I was driving my Echo and hypermiling it coming back home on a 55 MPH road and P&Ging the oil would not even be hot enough to bother me at all when I changed it when I got home.
It would take 5 miles for the thermostat to open on that Echo and in extreme cases like when I got 167 MPG on another non hybrid car I owned the coolant temperature would fall off over the 3.3 miles on that drive since the engine was only running 36 seconds out of the 210 seconds it took to drive the 3.3 mile test road.

 

A week ago the low engine oil pressure light came on, my Prius prime 24 is 3 mouths old and 3300 km.
the oil was contaminated with waterthe oil was like "café crème" color.

Toyota roadside assistance towed the car to the dealer .
The dealer called me the next morning, telling me it was not covered under the warranty and i should
run the car with the ice only during the winter and i sould not make short trips in cold weather.

The problem is , i live 5 km from my place of work and nobody told me at the dealership and, neither in the owner's manual
that you should not make 5 km trips in winter time.

I had a few cars before, all of them internal combustion engine, some diesel and others gasoline. I never experienced a problem like this, if i would have known that before, i migth have made another choice.

Anyway a week later the dealer called me back and told me i would be reimbursed they will send me a check. Happy ending !?!
For the rest of the cold season i will be monitoring the oil closely like an old beaten car of the 70's and, i will try as much as it is possible to force the car to run with the ice .

Pierre in Montréal

 

It's a side effect of Toyota's newer engines becoming more and more efficient. Older engines generated more waste heat that got the oil hotter easier to boil off the excess moisture in it. The easiest way to deal with the situation is to find an excuse to take a longer trip(~30min) at highway speeds in HV mode once every week or two during the cold months. Let the engine get good and hot for at least 30min to boil out any moisture. Problem solved.

 

Am I allowed to say I feel quite disappointed by such issue!? Can it be considered a design flaw, since it occurs when the car is used within its specs?
Is it officially documented? Can we file an official complaint?

 

TSB came out in 2021.

 

unbelievable it is not covered by the warranty...

 

Short trips aren't good any car with an engine. Such may not be considered usual use by the manufacturer. It is one of the things that trigger the extreme use in the maintenance schedule and changing the oil twice as often.

 

Since it is a legal issue (no money from the warranty), I would expect a countermeasure to be implemented...somthing like a cumulative counter of short trips to trigger a warning.

 

Or just intentionally run in hybrid mode at least one day per week. No need to go out of your way then, drive excessively.

About once a week driving our hybrid 2010 is our norm now, and if and when we need to drive somewhere, if possible we’ll do some shopping the same day, heavy/bulky items in particular.

 

Just running in hybrid mode might not be enough, depending on your particular driving habits and route. If your route is lower speed with lots of stops and starts, the oil won't get hot enough to boil out the moisture that was built up over the previous week or so. And it's not enough to just reach full temp. The oil doesn't just magically disappear the instant the engine temp reaches 100C. It takes time at full temp to completely get all the moisture out. How much time depends on how much moisture there was in the oil, and that depends on how many short trips were taken and how cold the ambient temps were.

Now, this all is only needed if the temps are well below freezing, and the car has mostly been used for short trips. It's generally not needed when the temps are above -5C because condensation in the crankcase isn't quite as bad at normal temps. It happens, but it's typically not enough to cause a problem.