[Captain Blight]

For my 2022 PHEV I am planning on changing the oil every 4,000 miles or 1 year, whichever comes first. (I'm retired, so not much driving.) I had the dealer only fill the oil to the middle of the dipstick hi/low measure to allow room for dilution without risking blowing seals. I'll periodically check the oil level and change the oil earlier if necessary. I also bought Mobil 1 "Hybrid" oil at Walmart and did a BYOO (Bring Your Own Oil) to the dealer. Mobil claims that the Hybrid synthetic oil can better deal with dilution by gas or water.

I switch to Hybrid/Sport mode on the freeway to heat the oil and have more reserve power quickly available if needed. The car will still drop into EV mode when cruising on level ground.

 

[Captain Blight]

Hi Captain. In my experience, when driving in Sport mode on freeway, the car never goes in EV mode, unless I'm coasting (downhill). The moment I touch the pedal even slightly, it starts the ICE.

I'm old school. (And old.) I was taught to drive like there was a raw egg between my foot and the accelerator pedal. (This goes back to the days of carburetors, where pushing on the accelerator would squirt gas into the throat, reducing gas mileage.)

 

[Captain Blight]

As way of an explanation and for anyone else reading, driving longer won't get any fuel that has entered the oil out, or burn it off. Once it is there it's there till you change the oil.
If you think about it, to burn it off would take very high temperatures of the oil, I would hope no one's oil gets that hot.

What has to happen is to try and prevent as much fuel from getting in to begin with, and that means the engine warming up to operating temperatures for awhile as often as possible rather than it starting for successive short periods. That will burn off what is getting past the seals before it can.
Assuming the car does not have bad injectors, seals, crankcase etc the three main ways oil dilution worsens are;

• Low operating temperatures
• Frequent short-trip driving
• Excessive idle time

It may have risen (or dropped) to the level of "conventional wisdom", but I've see the recommendation to get the oil hot on quite a number of web sites, including some of the "oil gurus." It seems reasonable that doing so would drive off at least some of the aromatics.

The very nature of a PHEV results in low operating temperatures, frequent short run cycles and (in winter) extended idle time for cabin heat. On one of the other threads somebody knocked a few of my brain cells together and I realized that this was the very definition of "severe" driving conditions.

 

[Captain Blight]

I will say I have seen that referenced I think If you could show me a link because If your oil is getting hot enough to burn off fuel you have a bigger problem!
Getting the engine hot stops the dilution (or greatly minimizes) by the heat keeping moisture/fuel from getting in to begin with, dripping down the walls of the cylinders burning more efficiently.

This was my first hit on a Google search. What's even more interesting is the assertion that using higher octane gas will reduce/eliminate the oil dilution problem (due to changes in ignition timing, not engine temperature).

https://bobistheoilguy.com/forums/threads/how-hot-does-an-engine-need-to-get-to-eliminate-fuel-dilution.303573/

Another thread from BITOG.

Fuel Dilution "Burn-Off"

I've spent far too much time wandering the internet trying to better understand the causes, effects and remedies for fuel dilution of engine oil, particularly in DI/TGDI engines. My Honda CRV is one of these and certainly has the issue. One of the oft-repeated bits of advice here is that a...

bobistheoilguy.com

Anecdotal, but interesting. [Video title "Eliminated Oil Dilution w/91 Octane Fuel? - 2017 Honda CR-V - Oil Sample Results! - #2". Have to click through to watch on YouTube.]

With the low fuel usage of a PHEV, using 91 octane gas wouldn't be a terribly expensive experiment.

 

[Captain Blight]

I dismiss the higher octane too, these cars adjust the timing.

That's actually the point.

From the first link above:

This is the key. NO turbocharged, high compression engine should be ran on junk 87 octane fuel, regardless if the darn manual tells you that you can! All these manufacturers coming out with these turbocharged engines and very high compression using 87 for efficiency is dialing the timing back so far it is causing a multitude of other issues. LSPI and dilution being two big concerns. Run 91/93 octane fuel and flog the thing once or twice a month as in the old "Italian tune up" and many of these issues will cease to exist.


It is more the A:F ratio than the timing. They run much leaner on higher octanes.

 

[Captain Blight]

Keep in mind my remarks are talking about today's cars not 5 years ago or more etc...

Actual experts I read say unless the manufacturer says using higher octane will benefit, using more will not make a difference. As an example -

Direct from Garrett
"Does it require premium fuel?
Not at all. Fuel requirements are set by the manufacturer but boosted vehicles don’t require anything different from their naturally aspirated counterparts."

Turbocharging Facts from Garrett Motion

How does a turbocharger work? A turbocharger takes, otherwise, unused exhaust gas from an internal combustion engine and uses it to drive a turbine that

www.garrettmotion.com

Jeep for instance does mention when towing in very hot weather 91 octane may give better performance....

The "higher octane doesn't make a difference" statement refers to engine knock. The Garrett article doesn't even mention knock.

The assertion (and that's all I'll give it at this point) on BITOG and elsewhere is that higher octane fuel allows timing to be less retarded and enables the engine to run using a leaner Air:Fuel mix, supposedly resulting in less dilution.

 

[Captain Blight]

I guess we are just not seeing what the other is saying. To me the statement is very clear by a major turbocharger manufacturer.

Does it require premium fuel?
Not at all. Fuel requirements are set by the manufacturer but boosted vehicles don’t require anything different from their naturally aspirated counterparts.

All three of these things can be true:

1) Turbos don't care about octane.
2) Modern engines don't require high octane gas to avoid knock. They will retard timing and supply a richer air:fuel mixture to eliminate knock.
3) A modern engine running on gas with an octane higher than 87 will adjust timing (less retarded) and air:fuel mixture (leaner) to reflect the combustion characteristics of that fuel.

It has been asserted that less retarded timing and a leaner air:fuel mixture will result in reduced dilution of engine oil by fuel.

 

[Captain Blight]

If the car is tuned by the manufacturer for 91 octane, and you put 87 octane in the tank, the knock sensor will detect knock and retard the timing. Then when you put in 91 or higher, the ECU will no longer sense any knock and the timing will be advanced back to the values programmed in the ECU maps.

But if the car is tuned by the manufacturer for 87 octane and you put 87 in the tank, the timing will be set as programmed in maps in the ECU, knock won't occur, and all is well. If you put a higher octane in, the car will still set the timing per the ECU maps just as it did with 87, and you have wasted your money.

The assumption in your point (3), that the engine will keep advancing the timing right up to the point of incipient knock is not correct. It will only do that if you use lower octane fuel than the car has been tuned for. Since even a little bit of knocking can cause engine damage over the long term, it's something that the engineers want to avoid.

It appears that this Toyota engine does adjust timing to take advantage of octane higher than spec.

https://www.rav4world.com/threads/higher-octane-fuel-and-ignition-timing.320457/

From a Lexus forum thread: I have been using premium (91-93), but this morning thought to check the owner's manual. It calls for a minimum 87 octane which is "regular" and goes on to recommend 91 octane for "Improved Performance". This suggests that Toyota used a knock sensing ignition timing system that advances and retards ignition timing if it senses engine knock or pre-ignition if lower octane fuel is used.

Key terminology for different engines appears to be "open loop" (uses tables) vs. "closed loop" (uses oxygen sensors and knock sensor to optimize timing and air:fuel ratio for the grade of fuel).

 

[Captain Blight]

I'm also low milage driver. At the dealer they told me to come for oil change every 6 months.

Oil change interval is based primarily on miles driven and whether the driving conditions are considered "severe." (With "at least yearly" sort of an unofficial outer bound.) The 6 month recommendation from the dealer is based on their revenue, not the health of your engine.

 

[Captain Blight]

Not sure if you saw my update, but I took my Tucson to the dealership early this morning for an oil change, and the service agent said to follow the oil life monitor on the car and not the six-month "severe" schedule in the manual. He said that they'd be happy to do the oil change but that it'd be a waste of money, so I decided I'm going to wait until the oil life gets below 10 % before getting it changed.

I was impressed that he didn't recommend service when I didn't need it.

But did he actually use the dipstick to check the oil level for possible fuel dilution.............which is the reason some/most/all HEVs and (especially) PHEVs need to follow the Severe oil change interval.