Oil level went this OCI. First time this has happened. As suspected there is fuel dilution. Maybe from the abnormally cold winter weather and recent short tripping. Going to take it to the dealer before the 60,000 mile Powertrain warranty is up so I can get the event on record if nothing else. More to come.
‘21 Toyota Sienna/ A25A-FXS / 55,000 miles / Pennzoil Platinum 0w16 / 5,000 miles
- Thread starter ATex7239
- Start date
The lab says the fuel dilution has caused the oil to get a grade thinner (0W-12?). I know your vehicle is speced for 0W-16. But if it were me, I'd be running a viscosity with higher HTHS to provide a margin of safety for wear protection in case of fuel dilution.
I most certainly will if this issue continues.
I suppose even the king of reliability (Toyota) isn't out of this whole Fuel issue in newer vehicles. Part of the reason is pushing more power out of the smaller engine injecting more Fuel but not all is burned. This is unfortunate & it's not just your Sienna engine issue. The good thing is that it appears there is little to no wear under the circumstances. You mentioned cold weather so I would expect this to be more of an issue in MN but not so much in TX as an example. The short trips can add to it as well. Here's to hoping the mechanics "Find" something that is causing the extra fuel injector or? but I have my doubts it's anything out of the ordinary with current gen vehicles.
This OCI was from December to March. And it has been an unusually cold winter for Texas. Not saying that is the issue, but it is notable.
When you see the Toyota dealer, you may wish to be assertive, and ask them to fix the issue which might still be covered under warranty (not just to record it on your account). Even talk with the Service Manager politely, and say you love Toyotas and you really like the dealership. But if he could have his best technician diagnose the issue and fix it under warranty, it would make you want to buy more Toyota's in the future from that dealership. I know it's a little BS, but it might help.
Have you tried actually driving it until the motor warms up? Everyone is quick to blame the oil without looking in the mirror at their driving habits.
Newsflash, even thicker oil suffers fuel dilution if you don't drive your car hard enough.
Newsflash, even thicker oil suffers fuel dilution if you don't drive your car hard enough.
Yes. And I don’t see where the oil was “blamed.” Keep in mind it is a hybrid so the engine turns on/off constantly.
Please keep us posted. BITOG is such a great site, we all learn about common issues with other vehicles and it helps all of us become smarter and more educated across a wide range of vehicles.
True, but a 5W-30 would become a 5W-20 (which is not too bad), but a 0W-16 would become a 0W-12, and that tiny HTHS number over a 10k OCI could be catastrophic.
I don't think there's anything to fix. If his fuel trims are within a normal range and there are no drivability issues, it is working as designed.
Toyota's idea of using both port fuel injection + direct injection to limit fuel dilution may not be working well in the cold weather.
The fuel dilution thinning the oil to a grade below 0W-16 is concerning, since Toyota recommends 10k OCI in these engines.
For a significant portion of the 10K OCI, the oil might be a grade below 0W-16. The long term engine wear from that could be an issue, especially after 100k miles in an 8 passenger minivan which will be under heavy load for a lot of its life.
If I owned a 2021 Toyota Sienna, I would check the owner's manual for the same engine in Europe or Australia. If 5W-30 is allowed for the same engine in those regions, I would use it, and do 4k OCI. That might help mitigate this issue and allow these vans to go 300k miles like the older Sienna's.
The fuel dilution thinning the oil to a grade below 0W-16 is concerning, since Toyota recommends 10k OCI in these engines.
For a significant portion of the 10K OCI, the oil might be a grade below 0W-16. The long term engine wear from that could be an issue, especially after 100k miles in an 8 passenger minivan which will be under heavy load for a lot of its life.
If I owned a 2021 Toyota Sienna, I would check the owner's manual for the same engine in Europe or Australia. If 5W-30 is allowed for the same engine in those regions, I would use it, and do 4k OCI. That might help mitigate this issue and allow these vans to go 300k miles like the older Sienna's.
Last edited:
Well, I have theory that 10K oil changes for most hybrids are actually not applicable, especially in a heavier vehicle. The ICE by design automatically falls into the severe category. The ICE stops and starts constantly and also while under load. The engine will never consistently runs like a normal set up. Which is, in my opinion, similar to many, many short trips over and and over again. Hence why I go with 5K and always have with the vehicle. That is just my theory anyways. If this issue continues I will be moving to 0w20 or 0w30 mitigate the fuel dilution.
A wise choice in my opinion. I am not a big fan of 20 weight oils, as their HTHS of 2.6 is right on the borderline of adequate protection.
30 Weight oils seem to have the right HTHS for excellent protection even in heavy duty applications.
I’ve been running 16
What event is there for the dealership to record?
Did the specified oil grade completely fail to adequately protect the engine? No.
Did you experience any increased engine wear during this run? No.
So is there any negative side effect from the fuel dilution seen in this UOA? No.
what’s the problem? Either you trust the manufacturer of your engine and blindly run the oil for 10k miles and accept the fact that the engineers are complete MORONS who purposely designed this engine to fail just after the warranty period is up so you go and purchase another one and do your part in stimulating our pathetic economy for another 60,000 miles OR you take matters into your own hands and run THICKER LUBE. 
Nobody is going to be ripping apart the block and sending out the fuel injectors for testing to insure they’re operating properly and not leaking when they shouldn’t.
Nobody is going to be testing spark plugs and coils to make sure they’re firing at 100% to insure they’re burning all the fuel like they should.
There’s nothing to inspect or investigate in these situations. It’s a combination of engine design and end user usage that’s to blame.
Until I see UOA of a healthy engine producing low wear with ZERO FUEL and then outta nowhere the next UOA now with a good dose of fuel dilution added into the mix and INCREASED Engine wear showing… I don’t see how the typical fuel dilution numbers that we see in these reports is anything to freak out over.
Similar threads
- Locked
