Oil change intervals - endless topic

[acdii]

ICE is ICE when it comes to oil, the variables though are on/off cycles, and temps. An Otto cycle runs up to a set temp and stays there, where the Atkinson cycles frequently and never really stays at one given temp. It is possible they have a category based on its cycle, Otto vs Atkinson.

[alpha754293]

ICE is ICE when it comes to oil, the variables though are on/off cycles, and temps. An Otto cycle runs up to a set temp and stays there, where the Atkinson cycles frequently and never really stays at one given temp. It is possible they have a category based on its cycle, Otto vs Atkinson.

 

Not sure how true that is.

 

The only "real" difference between the Otto and the Atkinson cycle is when the exhaust valve opens and when the intake valve closes. (i.e. the exhaust valve stays closed for a longer period so that you can extract the most work out of the power cycle); but due to the "late" exhaust valve (relative to the Otto cycle), part of the exhaust gases will end up getting pushed out the intake as well as the exhaust which eats into the compression work of the compression cycle.

 

The temperature thing might be a function of the Atkinson ICE being turned on and off, but not necessarily due to the Atkinson cycle itself. (There's really nothing that says that you can't do it with an Otto cycle engine as well, but since you are maximizing your work output (from the so-called "extended" power stroke), you get "more" for low(er) power, intermittent use than the exhaust losses from opening the exhaust valves "early" (when compared to when the exhaust valve opens for an Atkinson cycle engine) you get from an Otto cycle engine.

 

So if the used oil analysis is based on how much "stuff" is in the used oil (or how much of it has changed), you'd have to know the chemical reaction rates of the Atkinson cycle engine in order to not mis-read the results. (And yes, the calibration presumably, would matter greatly).

[acdii]

Well, I send them a question so, wait for an answer. I really dont think it will make much difference. In fact, unless there is fuel or particulate matter in excess of standard testing, the oil "should" actually last longer mile for mile. Heat is what causes oil to break down, so the cooler running cycles of the Hybrid should also provide an added benefit. So unless the stop/start cycle is causing fuel to leak into the oil, dont think there is much else to worry about.

[alpha754293]

Well, I send them a question so, wait for an answer. I really dont think it will make much difference. In fact, unless there is fuel or particulate matter in excess of standard testing, the oil "should" actually last longer mile for mile. Heat is what causes oil to break down, so the cooler running cycles of the Hybrid should also provide an added benefit. So unless the stop/start cycle is causing fuel to leak into the oil, dont think there is much else to worry about.

 

My only caution to the anticipated reply is to make sure that their reply is logical and makes reasonable sense based on how the two different ideal thermodynamic cycles fundamentally operate.

 

The proof of it should be able to be demonstrated using third-year thermo; and ad simile way of calculating BMEP, you should also be able to calculate the break mean effective TEMPERATURE. As for running at a "set" temperature - THAT might actually be driven by external factors (i.e. emissions, NVH, part/component durability) than because of the different thermo cycles in and of themselves.

[acdii]

Their response is the tests are the same based on the fuel type, not engine type. They dont really care on what the engine does, but on what is in the oil, and that is whats most important. The packages, particulates, and contaminants are what they test for. Based on the levels of each, they can determine engine wear, and life of oil. If they read higher than baseline readings of iron and aluminum, then something is wrong with the engine, abnormal wear. If they read higher than normal readings of silicon, there may be a leak, or a recent repair using silicone gasket was made. If they see some packages are lower than baseline they would recommend a shorter change interval and after 3-4 samples taken, you have a good understanding of just how far you can go between oil changes, and that is the key to getting the samples tested.

[alpha754293]

Their response is the tests are the same based on the fuel type, not engine type. They dont really care on what the engine does, but on what is in the oil, and that is whats most important. The packages, particulates, and contaminants are what they test for. Based on the levels of each, they can determine engine wear, and life of oil. If they read higher than baseline readings of iron and aluminum, then something is wrong with the engine, abnormal wear. If they read higher than normal readings of silicon, there may be a leak, or a recent repair using silicone gasket was made. If they see some packages are lower than baseline they would recommend a shorter change interval and after 3-4 samples taken, you have a good understanding of just how far you can go between oil changes, and that is the key to getting the samples tested.

 

Ahh...so the analysis isn't like a full mass spectroscopy/gas chromatography, but rather by particulates and contaminant matter. Interesting. So it doesn't look at WHAT the engine is doing to the oil, (chemical changes), but just solid matter/depositions.

[acdii]

Yes, its used for determining your wear and change intervals. If you want a full blown analysis, it would cost a whole lot more than the $20 or so they charge. Like I mentioned before, you only need to have a few samples done in a row to determine your change interval and engine wear, then depending on how often you change oil every year or so have one done.

[alpha754293]

Yes, its used for determining your wear and change intervals. If you want a full blown analysis, it would cost a whole lot more than the $20 or so they charge. Like I mentioned before, you only need to have a few samples done in a row to determine your change interval and engine wear, then depending on how often you change oil every year or so have one done.

 

Yeah...once again - I'm forgetting about the fact that I'm an engineer and that I also have some (limited) access to chem labs and GC/MS. And for $20, it's not a bad deal at all.

 

Like I've said before (which I learned from my engines prof) - changing your oil more frequently than it is necessary will never hurt your car (assuming it is done right every time). It'll only hurt your wallet.

[acdii]

One thing I learned, changing the oil sooner means it comes out cleaner and is easier on my filters for when I pump that used oil into my recycler. I then mix it with diesel and run it in my tractor. I can turn 5 gallons of diesel into 15 gallons of fuel. :) Great way to get rid of WMO.