Author Topic: Engine Oil FAQ  (Read 23116 times)

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Offline S204STi

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Engine Oil FAQ
« on: February 09, 2008, 08:03:58 pm »
Intro
I want to start this essay by pointing out a couple of things.  First, I am not an engineer; I am only a mechanic who is interested in forming a basic understanding at a technical level, so that I can intelligently form opinions and inform others.  Also, I am in debt to a number of people who have gone through the time, money, and effort of a higher education and who have studied and written so much on this topic.  Thanks must go to General Motors dealer training, members of Bobistheoilguy.com (there is actually a lot of unbiased info there), members of NASIOC.com, Howstuffworks.com, and others.

What is engine oil?
Engine oil has several key ingredients which allow it to be effective in an internal combustion engine (hereafter referred to as an ICE or just Engine).  The primary component is the Base Stock.  This is the refined hydrocarbon oil that is supplied to the manufacturer.{1}

There are two types of base stock, each with different grades.  Mineral or "dino" oil is the most basic type, and comes in three grades:  Group I, Group II, and Group III.    Grp I is very rare these days; almost all motor oils that meet the latest API and manufacturer specs are at least Grp II.  Grp III is controversial, because these are allowed to be marketed as synthetic oils.  One example, and the primary offender in this, is Castrol Syntec.  It is not bad oil by any means, but the marketing nightmare it has created is worthy of a whole new thread, so I will leave this with the fact that Grp III is easily an excellent base stock, in that it is the most heavily refined without being considered a full synthetic.{1}

The second type of base stock is called Synthetic.  These come in two grades:  Group IV, and Group V.  Group IV base stocks are PAO (Polyalphaolefin) based oils.  In the most basic terms, these are hydrocarbons that have been broken down into their most basic parts and recombined to form a "perfect" hydrocarbon oil.  Group V stands for a "catch-all" description of synthetic oils that are not PAO based, and often are formed from esters.{1,4}

The base stock represents about 80% of an oil (varying by manufacturer).  The rest is  made up of Viscosity Index Improvers, acid neutralizers, sludge inhibitors, thickening inhibitors, dispersants, detergents, seal swell agents, and anti-scuff additives.  This is a broad list, but thankfully the names are fairly self-explanatory. For example, detergents chemically bond with contaminants, while dispersants suspend those new molecules in solution. Anti-scuffing pertains mainly to cold-start conditions, where there is only a relatively thin film of oil available to prevent wear.{1}

All in all, a very complex creature.

What does oil do?
I think a valid second step would be to discuss what exactly oil does in an engine.  Primarily, oil acts as a lubricant.  It creates a boundary layer between metal parts to prevent them from actually touching.  It is a testament to how oil does its job in that you can disassemble an engine with hundreds of thousands of miles and still see the machined cross-hatching on the cylinder bores.{1}

The next valuable service that oil performs is cooling. Yes, most of the cooling of an ICE is created by the cooling system itself.  Yet the coolant passages cannot reach all of the motor, and some parts such as the valve-train see no cooling at all other than what motor oil supplies.  The valvetrain is sprayed with a perpetually refreshing coating of oil, while the undersides of the pistons are typically splashed or sprayed with oil as well. Oil is therefore also essential as a cooling aid.{1}

Engine oil also helps seal the combustion chamber.  The combustion event is a very violent action, and creates significant pressure.  The metal rings that encompass a piston could not seal properly if there was not a layer of oil helping.  This is also why oil becomes contaminated with time, or burns off causing the need to add oil occasionally in some engines.{1}

Last but not least is the inhibition of corrosion.  Bare metal, when exposed to moist air, corrodes. That corrosion leads to pitting, changes in clearance, and insoluble contaminants. Oil forms an air seal against those effects.{1}

Dispelling Myths.
To begin; the 3,000mi oil change is effectively dead.  Oil has come a very long way over the years.{1}  We've come from API SA rated oils to S(x), which represents numerous revisions.{6}  Each revision has demanded greater performance in a variety of areas, including:  cold pump-ability, cold start protection, viscosity retention/breakdown protection, fuel economy, overall wear protection, shear stability (i.e. actual viscosity in high temperature, high sheer situations), sludge control and others that I'm sure I'm missing.{1,6}

If you peruse a site such as www.bobistheoilguy.com/forums you can find countless used oil analysis (UOAs) showing that even with a prolonged oil change interval there is still plenty of additive reserve, good viscosity, and low wear metals such as lead and copper.{2}  This may be purely anecdotal, but consider this:  General Motors has seen fit to equip their vehicles with an oil life monitoring system (OLM).  I will discuss this system in the next section.

Other myths have to do with the whole synthetic/mineral oil debate.  Some claim that sythetics should not be used during engine break-in.  However, at a given viscosity synthetic oils are not going to lubricate better than dino oils (according to GM engineers).{1}  Also, the barrier film doesn't seem to be any different for either oil.  Finally, many OEMs use synthetic factory fills, and if there were any issues with engine break-in you'd think that wouldn't be the case.{1}  With all of that said, there is still some debate due to the fact that many engine builders recommend special break-in oils, etc.  The theory is that synthetics tend to protect against scuffing much better than dino oils.  I don't know where this comes from, but I wanted to present it to you the reader for your consideration.

Another is that switching to synthetic in a high-mileage motor will cause oil leaks.  This may be somewhat true, but only because the synthetic oil "found" a leak that was already forming.  What I mean is this; conventional base oils have many molecules of various sizes.  This makes for a fluid that may not seep as readily through a surface, because the larger molecules form a bit of a barrier.  Synthetics tend to have molecules of a similar size.  Therefore it stands to reason that synthetics could tend to seep more readily through a surface, particularly if there was already a gateway.  That said, there is nothing about synthetics that would cause seal failure.  If anything, some Group V synthetics could actually help seal an engine leak, since the esters that they are based on are used as a seal swelling agent in the additive pack of most oils.

Oil Life Monitoring, and what it means for you.
The GM OLM has been in constant use and development since the 1988 model year (making this 20 years total at the time of this post).  Additionally, GM lubricant engineers see 900+ UOAs a year from all makes and models, analyzing each one to determine whether or not the OLM calibrations are working effectively.  Multiply that by the number of years, and you get roughly 18000 UOAs.  The fact is that oil analysis is a very powerful tool, assuming you can accurately assess the information gleaned from one.{1,2}

The OLM uses a multitude of factors to determine the oil life percentage remaining.  These include ambient temp, engine coolant temp, intake air temp, length of trip, engine RPM, etc.  The OLM is calibrated at the factory to assume the correct amount of good quality oil.  Whether it is synthetic or not is irrelevant, which I will explain later.  Also, the OLM is calibrated to allow a 20% buffer.  Technically the owner's manual states a 600mi buffer, but in reality vehicle miles have little to no bearing on actual oil wear.  Therefore I point out the actual buffer.{1}

Even with that buffer, many owners are going for well over 5000 miles between changes; a new GMC Acadia that I worked on yesterday had over 8000 on the clock and still indicated 3% oil life remaining (or effectively 23%).  This is eye-opening for me, especially considering the fact that GM is so religious in maintaining a safe margin of error in the calibration.  *20160205 revision; note, GM actually had to retroactively change the OLM programming for vehicles using the 3.6L V6, due to excessive drive chain wear.

I would like to add one caviat that GM included in SI Doc 864693, stating, "Never drive the vehicle more than 16 000 km (10,000 miles) or 12 months without an oil and oil filter change. The system will not detect dust in the oil. If the vehicle is driven in a dusty area, be sure to change the oil and oil filter every 5 000 km (3,000 miles) or sooner if the CHANGE OIL SOON indicator comes on. Reset the Oil Life System when the oil and filter have been changed."

Which oil should I use?
The best answer to that question is to dodge it...  Honestly, it's a matter of personal preference at this point.  Syn/Dino, Valvoline/Castrol; all of these choices can be confusing and somewhat daunting.  Let me help you with this.  If you take two oils of different brands of the same viscosity and API service rating, they should perform more or less the same in your motor.  True, there are some differences in additive packs or in actual viscosity at a given temperature.  But, they have to meet the same basic standards for performance, which means that either one should work fine in your motor.{1,2,5,6}

As for the synthetic vs mineral oil debate, look at this:  the base stock, assuming a closed environment, does not break down.  The main reason that oil needs to be changed is contamination.{9}  Moisture in the air and blow-by from combustion events are the main conspirators in the destruction of your oil.  They are the main reason for the additive packs in motor oils.  These additives are expended with time, which results in increased sludge, insolubles, and acids in the oil.  Also, multigrade oils which use a viscosity index improver to meet certain cold flow performance requirements can lose that ability as those VIIs wear off.

If you want to know why this is bad on an engine, just do a photo search for, "Toyota Sludge," and you will get a perfect visual of what worn oil will do.  But again, it is not the base stock that's wearing, its the buildup of contaminants and the loss of VIIs that keep the oil from performing the missions that I listed previously.

So, this means that your choice of base stock is less relevant.  That said, I still like synthetic for a couple of reasons.  For one, synthetics tend to have better cold flow.  This means that it can be readily pumped to bearing surfaces to maintain that boundary layer that I mentioned, even at very cold temperatures.  Also, synthetics tend to hold onto their viscosity longer even under high heat conditions.  This means that if you have a turbo or run constant high RPMs, the oil won't lose it's ability to maintain viscosity (and the boundary layer that comes into play).  These two factors however are only relevant to a small minority of car buyers/drivers.  Far more people live in balmy California than in Fairbanks or Breckenridge.

Is diesel oil ok for my gasoline engine?
In brief, usually.  So long as it meets the API certification that your owner's manual demands, it will be fine.  The main difference between them is the increased amount of ZDDP and detergents.  ZDDP is a detergent itself, but also adds a lot of phosphorous and zinc to the additive package.  ZDDP is an excellent anti-scuffing agent, which means that it is there to protect moving parts during startup, when there is not enough flow to maintain the boundary layer that oil normally creates.  Diesel engines tend to create a lot of soot in the oil, and also see incredible pressures compared to gasoline engines, hence this need.{1,2,5,6} I personally prefer to run diesel oils.


Logical Conclusions.
So you ask, "How often should we change our oil then"  Frankly, if you are not blessed with an OLM system then you should just follow your owner's manual.  I cannot emphasize that enough.  You will rarely come across a 3000mi interval in your manual (unless you own a turbo Subaru post-2007, but then those aren't real cars anyway).  Most likely it will say at least 5,000mi, frequently 7,500mi or in some rare cases as much as 15,000mi.  Back this up with oil analysis if you're nervous.

One could say, "Well, what harm could I do by changing the oil every 3,000 miles?"  Well, maybe not much, but you are wasting perfectly good oil, and costing yourself needlessly hundreds of dollars over the life of a car (and thousands over your whole lifetime!).  Remember the axiom, "If it ain't broke don't fix it?"  Yeah, that applies to oil as well.  Do what feels best ultimately, but keep in mind that it may not be necessary.

Note that if you are going to do a UOA yourself in order to determine your target OCI, proper technique is key to the most accurate results.  Per my Blackstone Labs directions, make sure to take your sample in the middle of the drain; in other words neither at the beginning nor end.  This minimizes contaminants that settled in the sump and may throw off the reading.

My UOA, number 1
My UOA, Number 2
My UOA, numbers 3 and 4


Revised 05/22/08 to add link to my first UOA.
Revised 02/28/08 for new info on UOA and synthetic break-in.
Revised 02/05/16 for new info regarding potential fallibility of OLM systems
Sources:
GM IDL course 102017.16D "Engine Oil". {1}
Bob is the Oil Guy forums.{2}
Oil 101 by Dr A.E. Haas{3}
NASIOC oil FAQ{4}
API info{5}
API pdf on oil ratings.{6}
« Last Edit: February 05, 2016, 08:16:47 pm by S204STi »

Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #1 on: February 09, 2008, 08:05:37 pm »
Any commentary or corrections from professionals/engineers/general know-it-alls welcome. :ohyeah:
« Last Edit: February 13, 2008, 09:05:37 pm by R-inge »

Offline CALL_911

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #2 on: February 09, 2008, 08:05:58 pm »
Damn, R-Inge. That's bloody awesome.

Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #3 on: February 09, 2008, 08:06:57 pm »
I will try to include a solid bibliography as well, so that people know this isn't just some half baked stuff I pulled out of my arse.

Offline the Teuton

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #4 on: February 09, 2008, 08:10:55 pm »
This makes me feel better.  My oil has about 6,000 miles on it right now, unfortunately.  But this oil dates back to May for the most part -- when I had my engine replaced.  It's getting changed this week, but should I be concerned?
2. 1995 Saturn SL2 5-speed, 126,500 miles. 5,000 miles in two and a half months. That works out to 24,000 miles per year if I can keep up the pace.

I don't care about all that shit.  I'll be going to college to get an education at a cost to my parents.  I'm not going to fool around.
She'll hate diesel passenger cars, all things Ford, and fiat currency.  They will masturbate to old interviews of Ayn Rand an youtube together.
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Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #5 on: February 09, 2008, 08:11:40 pm »
This makes me feel better.  My oil has about 6,000 miles on it right now, unfortunately.  But this oil dates back to May for the most part -- when I had my engine replaced.  It's getting changed this week, but should I be concerned?

Go to Blackstone Labs' website and get a UOA sampling kit.  Mail it to then with  $22, and see what they tell ya.

Offline the Teuton

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #6 on: February 09, 2008, 08:14:07 pm »
Go to Blackstone Labs' website and get a UOA sampling kit.  Mail it to then with  $22, and see what they tell ya.

Srsly?

Actually, I was wrong.  It has about 5,000 miles.  I had 159,xxx on the odometer when I got the car back.
2. 1995 Saturn SL2 5-speed, 126,500 miles. 5,000 miles in two and a half months. That works out to 24,000 miles per year if I can keep up the pace.

I don't care about all that shit.  I'll be going to college to get an education at a cost to my parents.  I'm not going to fool around.
She'll hate diesel passenger cars, all things Ford, and fiat currency.  They will masturbate to old interviews of Ayn Rand an youtube together.
You can take the troll out of the Subaru, but you can't take the Subaru out of the troll!

Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #7 on: February 09, 2008, 08:15:43 pm »
Here is an example of a UOA report:  Read first post

Offline the Teuton

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #8 on: February 09, 2008, 08:22:11 pm »
So 5,000 miles is a happy number then?  It looks like it.
2. 1995 Saturn SL2 5-speed, 126,500 miles. 5,000 miles in two and a half months. That works out to 24,000 miles per year if I can keep up the pace.

I don't care about all that shit.  I'll be going to college to get an education at a cost to my parents.  I'm not going to fool around.
She'll hate diesel passenger cars, all things Ford, and fiat currency.  They will masturbate to old interviews of Ayn Rand an youtube together.
You can take the troll out of the Subaru, but you can't take the Subaru out of the troll!

Offline The Pirate

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #9 on: February 09, 2008, 08:29:57 pm »
Way cool, dude!  :rockon: :ohyeah:

I must confess that I've been changing mine at 3000 miles for quite some time now.  I will be rethinking that decision.
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Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #10 on: February 09, 2008, 08:37:55 pm »
I change mine every 3750, just because Subaru changed their policy to include all turbo engines under the "severe service" maintenance category.  But as soon as the power train warranty is up I will rely on UOAs to determine the correct interval.

Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #11 on: February 09, 2008, 08:38:38 pm »
So 5,000 miles is a happy number then?  It looks like it.

Other reports have been happy with even higher numbers.  But if you want a hard and fast number, go with the one in your manual.

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #12 on: February 09, 2008, 08:45:05 pm »
They say 5000 to 7500 for "normal" driving.

But aren't most drivers classified as severe drivers?

Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #13 on: February 09, 2008, 08:46:15 pm »
They say 5000 to 7500 for "normal" driving.

But aren't most drivers classified as severe drivers?

Depends on how your manufacturer classifies "severe" but if you do, follow that recommended interval.

Offline Rupert

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #14 on: February 09, 2008, 08:48:28 pm »
I used to change the Miata's oil at about 3000 miles, because beyond that mileage, there would be too much HLA clatter. (The miata.net forums have a ton of HLA stuff for NA Miatas; it's a common problem).
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Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #15 on: February 09, 2008, 08:50:43 pm »
Right, known issues are a good reason to follow special intervals.  My idea here was simply to educate, but it seems like most people are getting caught up on my section concerning oil change intervals.

Offline Rupert

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #16 on: February 09, 2008, 09:16:34 pm »
Well, you didn't say in there, "With the exception of certain engine issues,...".

;)
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Offline S204STi

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Re: Oil: Finding the Facts (In development)(Sticky plz?)
« Reply #17 on: February 09, 2008, 10:26:51 pm »
Well, you didn't say in there, "With the exception of certain engine issues,...".

;)

I did however say to follow your owner's manual.  But you're correct, and it's mainly because I never heard of that before.  ;)

280Z Turbo

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #18 on: February 09, 2008, 10:29:52 pm »
I would say there are no facts about oil. Only opinions and anecdotal evidence. :lol:

I've heard that I'm destyoing my solid lifter camshaft in the Z by not using diesel oil. :huh:

Offline Secret Chimp

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #19 on: February 09, 2008, 10:42:02 pm »
I would say there are no facts about oil. Only opinions and anecdotal evidence. :lol:

I've heard that I'm destyoing my solid lifter camshaft in the Z by not using diesel oil. :huh:

Four-cylinder Accords all the way up to 1997 have adjustable lifters and recommend 5W-30 oil :P


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Offline S204STi

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #20 on: February 09, 2008, 10:43:22 pm »
I would say there are no facts about oil. Only opinions and anecdotal evidence. :lol:

I've heard that I'm destyoing my solid lifter camshaft in the Z by not using diesel oil. :huh:

Bullschmitt.

I've read a lot lately about that, and I will clue you in on why they say that.  Diesel oils have a very high percentage of zinc and phosphorous, via the additive ZDDP.  This is usually 1500ppm.  Even up till recent history, most gasoline oils had around 1000ppm ZDDP.  What is ZDDP you ask?  An anti-scuff and detergent additive, which tends to be most useful during cold starts.  The reason it's good for flat tappet and/or solid lifter cams is that there is a ton of pressure there and little lubrication from your fluids at startup.

However, even at today's decreased level of around 600ppm ZDDP in SM rated oils it is still a lot more than in the 50s when oldsmobile engines with flat tappet cams were failing, and ZDDP was first discovered as a necessary additive.  The reason it dropped from recent highs to a lower level at this time is because it was discovered that ZDDP contaminates catalytic converters.  So, manufacturers got together with the oil companies to reduce that additive to save money.  Many people will tell you that this is the death of good motor oil, but when a new oil standard is established they must be certified as backwards compatible with all previous oil certs, and all previous engine designs still on the road.  That means that flat tappet and solid lifter cams are certified solid gold with the latest gasoline engine oils.

That all said, if you want extra safety and a bit more confidence, diesel engine oils are very cheap and are generally always API certified for your gasoline motor.  Assuming the age of your car, it recommended something like SG or SH.  You could use the latest greatest or use some old API SL oil and still be way ahead of your minimum standard.

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #21 on: February 09, 2008, 10:43:50 pm »
It has something to do with additives they used back in the 70's vs. now, environmental standards, blah, blah, blah, etc.

Offline S204STi

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #22 on: February 09, 2008, 10:44:02 pm »
Four-cylinder Accords all the way up to 1997 have adjustable lifters and recommend 5W-30 oil :P

You can get diesel oil in many different viscosities, not just 15w-40.

Offline S204STi

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #23 on: February 09, 2008, 10:44:30 pm »
It has something to do with additives they used back in the 70's vs. now, environmental standards, blah, blah, blah, etc.

I explained it already, read my post.  :rage: :lol:

280Z Turbo

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #24 on: February 09, 2008, 10:46:49 pm »
I explained it already, read my post.  :rage: :lol:

That was posted 28 seconds after your post. I didn't get around to reading it.

Offline S204STi

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Re: Engine Oil FAQ (In development)(Sticky plz?)
« Reply #25 on: February 09, 2008, 10:50:46 pm »
That was posted 28 seconds after your post. I didn't get around to reading it.

That's no excuse!

Offline GoCougs

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Re: Engine Oil FAQ
« Reply #26 on: February 14, 2008, 08:25:29 pm »
Wow - that's something you could probably sell - and completely dead-nuts on IMO. I'll provide a bit of diatribe to echo your sentiments:

3,000 mile OCI is indeed a myth - "severe conditions" are cop cars, tow trucks, taxis and other such vehicles which spend a significant amount of time idling, as ultimately engine oil life is a function of engine run time. Such vehicles have a lot more engine hours per mile. IMO, if one isn't using their vehicle in such a manner virtually full-time, then it's not "severe" conditions. Either way, you're 100% correct - the OLM will tell the real story.

Synthetic's advantages are not near what the manufacturers claim. The only real advantages IMO are that it may last longer, and that it is available in wide weight ranges, such as 5W-50 which was used in the previous-gen M3 IIRC. (FWIW, my Accord manual says that even with synthetic the standard OCI must be followed or the warranty is void.) Synthetics have a slight advantage at minimum pumping temp (actually an ASTM spec), but even conventional 5w-30 will pump down to -30F (synthetic 5W-30 seems to be usually -35F to -40F). Conventional oils today are so good nowadays that 10,000 mile OCI are not uncommon (4 cyl Accord for example per my manual).




280Z Turbo

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Re: Engine Oil FAQ
« Reply #27 on: February 14, 2008, 09:02:42 pm »
The problem is that some cars in some conditions might benefit from 3000 mile oil changes.

There are so many variables that it's hard to make any blanket statements. It's hard to say.

I shoot for 3000 and I do it when I get around to it, just to be safe. :huh:

Offline GoCougs

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Re: Engine Oil FAQ
« Reply #28 on: February 14, 2008, 10:32:03 pm »
The problem is that some cars in some conditions might benefit from 3000 mile oil changes.

There are so many variables that it's hard to make any blanket statements. It's hard to say.

I shoot for 3000 and I do it when I get around to it, just to be safe. :huh:

Sure, but the conditions would have to be really extreme. Even the standard 7,500 mile OIC have a decent margin on them as R-inge noted.

The other issue I completely forgot about was oil filters - they're designed to be changed only every other oil change, but who does that any more?

280Z Turbo

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Re: Engine Oil FAQ
« Reply #29 on: February 14, 2008, 10:35:35 pm »
I always change the filter.

I use Wix filters too. They're supposed to be really good.