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Oil Retention in modern engines

My first engine build was an old Ford 289 in 1984. This was a class effort. There was very little oil left in the engine after draining the pan. This was a solid lifter, push rod, rocker arm valve train and of course single cam. Some may still remember these engines and simplicity. My most recent experience is with GM 2.4L Ecotec with DOHC, VVT, dual balance shafts, hydraulic lifters, oil squirters for pistons and chains, large oil galleries, and top side cartridge filters in a small 4 cylinder package. My tech said he typically adds an extra quart of oil, above what the sump requires after a rebuild. After seeing the three oil galleries and the size of the main and those in the cylinder head feed the lifter and VVT, I can believe it. Attached are photos of the cylinder head. This oil does not drain out during a typical spill and fill, and new filter. I did some oil analysis and found retention of 20% of wear metals, contaminates, particulates, and fuel dilution after an oil change. It required a second oil change to get down to acceptable levels. I estimate close to 15% oil retention for this small 4 cylinder engine. Are there any long term research on the negative affects of retention of these contaminents, oxidized oil, fuel/soot from GDI and wear metals, especially when manufacturers are pushing for longer drain intervals and reliance on Oil Life Monitors? I see an immediate decrease in viscosity, additive levels, and ability to neutralize acids in the oil within minutes of the oil change. My own investigation shows the introduction of GDI fuel dilution and soot caused a doubling of wear in the this engine generation, compared to port injected. I have started to perform Full Volume Oil Changes to remove 99% of the old oil to prevent this additional wear. Interested to know if there any research on this issue of higher oil retention.

VVT Oil Gallery

Wow! Good for you if you’re into that stuff so much. I don’t get into the engineering of my cars too much. When I want a “new” car, I buy one on Craig’s List for like 4 grand and drive it for 10+ years. They’re already engineered!

I change the oil every 5,000 miles and fill with Mobil-1 EP and call it good. I don’t sweat over leaving a few drops of the “old” oil in there. Hexx, the old oil isn’t even dirty or worn out.

I’ve had oil tested at Blackstone Labs and they tell me my oil change regimen is overkill. My oil could go a lot longer. Don’t care, it’s cheap and easy to change.

I wish I could help more, but I try and save time, reduce stress in my life and have time for fun stuff. May the force be with you, though! Good luck!
:palm_tree: :sunglasses: :palm_tree:


Hi Brian_Sydnes:
Very interesting and impressive analysis you did. Reading it does trigger two thoughts

One is when you said you did an oil analysis after a spill-n-fill and determined the oil had 20% retention of various contaminates. How did you determine that? Was it simply a ratio of the amount of oil in the engine before the spill, and the amount you believe to be left over after the spill?

Second, I agree there may be some dirty oil left in the engine after an oil change (as it happens with many engines). Millions of vehicles on the road are following the manufacture’s schedule or OLMs, and they’re using single spill-n-fill. And there’s no sign of industry-wide engine failure from that.

I do understand your concern. However, if it were my vehicle, I wouldn’t lose sleep over it.

The OLM algorithm is validated by empirical testing. The fraction of residual oil diluting the fresh oil has already been factored into the degradation rate.

The fact you saw immediate effects means it’s cycling readily and not stagnating. I wouldn’t personally lose any sleep over it.

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Nice investigation! Yup, OLM is empirical data collected over millions of test miles and oil analysis by the manufacturers so it takes into account the dilution at changes. Considering how many people postpone or forget their oil changes, the engines today are pretty robust to contaminates in the oil. And oils are so good they protect these people well about 100K miles.

The thinking here is very similar to automatic transmissions. You can’t drain the torque converter with a pan drop but you are replacing about 60% or so of the trans fluid. 40% just stays in place. You have to assume the magnets and filter catch the bigger chunks and the fresh fluid replenishes the additive package. People, however, treat automatic transmissions like refrigerators… forget about it until it doesn’t work!

Thanks for responding. Not sure why you responded, as it added nothing to the discussion… Obviously this topic of oil cleanliness, vehicle performance and prevention of accelerated wear is not of any interest to you.

I don’t sweat over a few drops of used oil, either but 10-20% is rather significant.

This topic is important to me, regardless of your own unsolicited opinions.

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Very good read, I have the 2.4 Ecotec in my 2013 Equinox. The pistons, rings, and timing chain were replaced at 42k miles in March 2016 due to high oil consumption. I’ve made a habit of checking the oil on a regular basis and found if I checked the oil a few minutes after shutting off the engine the oil level was near the bottom of the dipstick. It would take a few hours for the oil to drain back to the oil pan. I got into the habit of letting it sit overnight before checking the oil for the most accurate reading.

These days I change the oil (every 5k) cold after letting the Equinox sit overnight, then I let it drain for a few hours. This gets about 4.5 qts out of the engine and I assume the other 1/2 qt was consumed over the 5k miles between changes.

This is the first engine I’ve seen exhibiting this behavior.


Ed B.

I’ll bite, how do you achieve a full volume oil change if 20% of the oil remains in the engine?

And are you about to sell a magic device on late night television to overcome this “problem”?


Thanks for responding. I originally learned of it when GM rebuilt my engine. I provided my own oil for the work. I had the cylinder head rebuilt by 3rd party so I got close look at the galleries and oil control passages. The tech said he typically adds more oil to the engine than what is specified in the service manual because of this. I sampled the old oil, the original new lube reference, as well as the new mixture to get percentage or fluid mixing based on known quantities contaminents. What I found was consistent what the GM tech reported.

Actually many manufacturers have and are still struggling with the negative side affects of Gas Direct Injection. We will probably see exhaust soot filters on cars in the very near future. GM seriously underestimated their OLM, resulting in very long drain intervals and engine failures. This occured from 2010-1013, where they finally updated the engine calibrations. I have found the new method to be inadequate due to fuel and soot dilution, and customer are still seeing excessive wear and component failures before 100k miles.

Have you specifically looked for research on negative affects of larger quantities of residual oil? The industry has cleanliness standards for oil but not when it is mixed in the engine.

Its not your vehicle, and I don’t lose sleep over it. I see many people on my forum who try to follow maintenance schedules and OLM only to have their engines fail or begin burning oil excessively shortly after their warranty is up.


Twin Turbo, GM had to update their ECM calibrations to including actual distance and time, rather than just rpm and temps. This was due to a high percentage of engine failures due to excessively long drain intervals. So much for impirical testing. Do you have any information to support that 10-20% of old oil has been factored into what you call the degradation rate, what ever that means.

Cycling readily and stagnating??? I never said I lost sleep over it.

Mustangman, I doubt seriously any manufacturer take millions of test miles to determine OLM. GM is very example of a failed OLM design. GDI technology has been a major problem for manufacturers and engine robustness has suffered. I have over 500 oil samples from the same engine class showing twice the wear rate as non GDI designs. Real=world consequences of oil contaminents include engine and component failures due to high fuel dilutions and soot, and now API has come out more tests and specs to show the affects of soot and chain wear.

The 1st Generation Ecotec engines were known to easily last over 200k. Now you are lucky to get 100k without a chain failure or worn out rings even with API SN Dexos full synthetic oil.

GM has seen their fair share of transmission problems. They thought the sealed transmission was a great idea and the filter would last for ever. Who would pay $1500 to change a filter or clean the sump.
Do you have anything supporting or can direct me where I can find extensive testing of residual contaminents in oil over the long term.

Not sure why I responded?
Sorry, You asked, and I thought you’d gain something from my input (I guess I expected you’d read between the lines).

Not of any interest?
Oil and oil cleanliness is important to me (Obviously?) Not everybody mails off oil for analysis as I’ve done. I change oil religiously (figuratively).

I’ve come to learn, as I’ve explained, in most instances if one changes oil every 5,000 miles then they will be more than good to go. Don’t sweat it (relax).

Still, You’re welcome!
:palm_tree: :sunglasses: :palm_tree:

Hi Ed B, I have a 2012 Nox and in 2018 GM rebuilt the engine for the same extended warranty. Many customer with the updated pistons from 2014 to 2017, either replaced or from the factory are experiencing the same accelerated wear. I have not seen that much a difference between a hot or cold when checking the level. Maybe one notch at the most. Always best to check in the morning. Elevating the front end will allow a little more out when draining. Another key is to replace the filter first, as it will drain the reservoir into the sump. Up to quart of oil will still remain in the engine between the oil pump and oil filter housing, the main oil galleries, and in the head. Those wont drain. Attached is picture of cylinder head VVT solenoid openings with the filter pulled and pan empty. If nearly all the oil drains out over night, we would have to prime the pump and pressurize the engine with an external pump before starting each day.

Hi OldTimer, you can achieve a near 96-99% volume change by simply performing a second oil change after 20 minutes of engine operation. This allows blending of the new and old oil. Although hard to find a shop, but some still have engine flush machines, made by Wynns. My Chevy dealer uses the Wynns transmission flush machine. In Asia I have seen similar machines.

Use a jug of SuperTech Full Synthetic oil for $13 and an extra 10 minutes of time. Keep the oil for use in an old grocery getter…

No I have nothing to sell you or help with your late night insomnia :slight_smile:

This applies to all engines.

Maybe Doc is listening. He has done failure analysis and might have something to add. I will admit that I have run a little new oil on a small engine or two just to flush stuff out of the block but I’ve never done it on a car. Usually oil I was going to recycle anyway.

I have used many different oil analysis companies over the past 30 years, and I have gone as far as 30k miles on an oil change with older engine designs. I do not like what I am seeing in term of contamination from several sources including my vehicles. I am not so confident that manufacturers care if vehicle last much longer than 100k miles . I have worked as an engineer and I am well aware of the cost/benefit/risk considerations that are made all the time.

I don’t have to read between the lines, your comments are plain as day, and they still do not add anything to the conversation.

I will pose the question again. “Are there any long term research on the negative affects of retention of these contaminents, oxidized oil, fuel/soot from GDI and wear metals?”

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Thank you, I guess. I appreciate you evaluating my opinion, sir or madam.

I’m no engineer, just a mere normal mortal who has excellent service from cars (up to 300,000 miles) and I don’t worry too much about retention. I go with results.

Oh, and speaking of "retention" and your persistence …
… oh, never mind. Good day! I hope it all works out for you.
:palm_tree: :sunglasses: :palm_tree:

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Yeah, there is lots of information out there documenting gm’s approach. The additional factors you mention were added decades ago. Gm engineers say there is 20% margin built into the % remaining number already. I read your post carefully. Do the same for mine…


Got quite the chip on your shoulder, don’t you?

I have observed, read and discussed with other engineers, otherwise. I was a former GM engineer. Data was collected from durability test cars. Thousands of them. For between 12,000 and 100,000 miles tests depending on schedule. A standard “100K equivalent” test is 26K miles. It only takes 38 test cars to get that first million test miles. OnStar provides a data stream for sold cars that also results in collection of test samples (even if you don’t subscribe). So the database is quite large from a manufacturer that sells about 6 Million cars a year and test a few hundred samples each year.

Did you miss the part where I posted…

So do you have the entire test background all the cars that resulted in those 500 samples? If not, you cannot draw any conclusions about the reasons behind the contamination results.

Why would anybody charge that? You clearly don’t know what “sealed” actually means.

Go do your own research. Bye!


Hi @Brian_Sydnes, welcome aboard. Thanks for starting your discussion. Folks here have lots of different types of experience, and often times disagree with each other. I must ask that you please remain respectful of others when disagreeing. Thanks.