Oil Change Intervals Objectively

[Blumlein 88]

Don't forget that oil viscosity changes with temperature. A typical 0w20 oil has a viscosity around 35-50 cST at 40* C, and 8-9 cST at 100*C. That's a big range! Even bigger when you first start the engine, it's more like 10* C or less! Given how wide that range is, it's hard to imagine how the engine could be picky about viscosity.

Well as captinbeefheart already said, put the wrong viscocity oil in some of these cars and you'll get codes on the cam phaser system. Get some trash in some of these very narrow passages and you'll get the same. Get a screen slightly clogged ditto. I don't know, but would guess they ignore or manage certain conditions until the engine reaches its normal operating temperature which for most cars is over a fairly narrow range. From monitoring oil temps in regular use on the road oil temp varies a bit more than coolant temp depending upon what you are doing, but it doesn't vary all that much. Meaning when warmed up the viscosity change is not much either.

 

[captainbeefheart]

In regard to VVT and viscosity, it's a closed loop feedback system where you have reluctance rings on the cam/sprocket/phaser to monitor it's relative position compared to crank. Now oil pressure is sent to the phasers through the control solenoid to adjust the timing, if the computer doesn't like where the position of the camshaft is it regulates the valve more or less open until it's where it needs to be. Basically what I am saying is it adapts to a certain point, oil thins out the valve just opens more to get the desired degree of change it needs. If the computer sees the commands being sent to the control valve and goes beyond a point, say full open but still not moving the phaser enough codes are set. Some systems will have the VVT not operate under too low/high oil pressure conditions. All this "wiggle room" is set around a specific oil type and typically you won't get any codes with slight changes in viscosity but some systems are finicky and the wrong type may reach an extreme point were codes are set. It's best to just stick with the recommend type of oil the manufacturer recommends. During open loop operation (cold start) I do not believe the VVT's are being activated and will just spin at their default position until closed loop operation is met.

Someone brought up direct injection, Multi-port injection cleans the intake valves where direct injection does not, many cars with direct injection will have dirty intakes and valves no matter how many times you change your oil. There are after market oil catch can kits that do a much better job of keeping your engine clean.

 

[MRC01]

...
Someone brought up direct injection, Multi-port injection cleans the intake valves where direct injection does not, many cars with direct injection will have dirty intakes and valves no matter how many times you change your oil. There are after market oil catch can kits that do a much better job of keeping your engine clean.

Some manufacturers, like Mazda among others, have air/oil separators in the PCV line installed from the factory in order to reduce intake deposits on direct injection engines (which have a dry intake). And other mitigating features, like valves designed to run hot enough to discourage deposit formation. Other manufacturers don't. If you look at the intake after 50k miles or whatever, you can see the difference.

 

[captainbeefheart]

Some manufacturers, like Mazda among others, have air/oil separators in the PCV line installed from the factory in order to reduce intake deposits on direct injection engines (which have a dry intake). And other mitigating features, like valves designed to run hot enough to discourage deposit formation. Other manufacturers don't. If you look at the intake after 50k miles or whatever, you can see the difference.

Yes my BMW has an oil separator but it does a pretty poor job and still greatly benefits from an added oil catch can. It's not just BMW but Mazda like you mentioned and others have the same issue. I can't tell if they just design the separators to do a good enough job to just get them out of warranty so it's another built in destruction point to make service money or drum up trade in's and sell you another new car? Or they just did a poor job of designing them? Most likely the former.

When these systems first came out we had no idea until we started to do tear downs for repairs, then we thought maybe the PCV system or separator were faulty but nope, all of them had deposit problems. There is a big aftermarket demand for these catch can systems for people that want to keep their engines clean so they can make it into the high mileage club.

 

[EJ3]

My friends foreign auto shop has a fleet contract and that's what they do. Some filters that aren't cellulose element design and use a high quality synthetic element claim they are good for 20k miles but we found that just using a regular wix filter at 10k and oil at 20k worked really good. It wasn't uncommon to see half a million miles on the engine. Disassembly of the engines were always extremely clean. All oil changes used the same oil, he had a 55 gallon drum of Mag1 synthetic blend that was I think $500, works out around $2/quart. It met ILSAC GF-5 which is all that was required and it proves you don't need to spend huge money on your oil to get high reliability.

Simple answer to anyone looking for oil is look in your manual for what specification rating needs to met, usually ILSAC, Dexos or API and get the cheapest stuff that meets that spec. Really nothing else matters.

To avoid jacking the car up twice you could just get a high quality synthetic filter and oil and just do both at 15k miles and I guarantee your engine will be fine. If under warranty I recommend following the manufacturers service intervals to avoid any issues. Once out of warranty do whatever you want.

The only real way to know for certain how far you can go while still maintaining oil quality is to send it out for analysis. Suck some out at 5k and see what the analysis says, move onto 7k, then 10k, etc... They make the reports very easy to read and have a little write up with their recommendations, for $30 I'm obsessed and the information is invaluable. They usually always state if they recommend going further between oil changes or the opposite less. If you are buying a used car I highly recommend sending the oil out to see what's going on.

Here is a sample report for people interested: https://www.blackstone-labs.com/wp-content/uploads/2019/01/Understanding-Engine-combined.pdf

As near as I have been able to determine, in the USA, the standard WIX filter is a top tier filter. As to checking the oil in a used car, if you are getting the used car from a dealership, the oil will likely be new & has not gone far enough to have enough contaminants to show anything. If from an individual, the oil is likely to be older & may show something (weather good or bad).

 

[captainbeefheart]

As near as I have been able to determine, in the USA, the standard WIX filter is a top tier filter.

Yes WIX makes a consistent high quality filter. Napa Gold filters are made by them by WIX.

For our Forester and Titan I use WIX and for the X3 I mainly get Hengst but have used Mann in the past which are also good filters.

As to checking the oil in a used car, if you are getting the used car from a dealership, the oil will likely be new & has not gone far enough to have enough contaminants to show anything. If from an individual, the oil is likely to be older & may show something (weather good or bad).

Agreed. Although if a dealer or private seller did change the oil prior to listing it for sale I think there is a good chance that it will still pick up some of the more serious issues like fuel or coolant contamination telling of something like a bad head gasket or cracked block/head. Yes wear metals will be too low to tell us anything of use. If they changed the oil make sure it's idling for a bit while talking and take it for a test drive all before grabbing an oil sample that way there is a better chance of catching a problem.

 

[MaxBuck]

I have an ICE car which is driven about 2000 miles per year. Use is split between short and long trips in a warm climate. It came with synthetic blend oil but now runs full synthetic. Everything I could find says never go more than a year between oil changes without regard to mileage. However, I have been unable to find any objective data showing how much slipperiness the oil loses simply due to the passage of time. Is such objective information available or is the one-year interval something left over from the days before synthetic oil, a manufacturer's CYA or an old wives' tale?

I recommend Googling "motor oil bible" and downloading one of the many free pdfs floating around. It tells you everything you need to know about engine lubrication.