|
Gress |
|
|
Ranger Gress's Great Oil Debate Documents and Threads Oil is like religion. Everyone feels strongly that there's is best, but few have convincing reasons as to "why" there's is best. When reading oil debates one sees a lot of "my engine likes < >" and "I've never had a problem with < >" as if an engine not blowing up provided any insights. Good lubrication depends on a number of variables, to include high temp viscosity, high temp shear and the anti-wear properties of the oil. OEM recommendations. What an oil OEM or vehicle OEM recommends is based on their priorities which may not be your priorities. Imagine a big table with 4 guys from accounting, 4 guys from marketing, 2 lawyers and 1 engineer. Those are the guys making decisions re. what oil to spec for your car. Examples: 1) Is gas mileage more important to you than engine protection? US car OEMs often spec lighter oil for their cars in the US than they do for their same cars sold overseas. This is apparently due to an attempt to squeeze tiny gains for the US "CAFE" fleet mpg standard. 2) Are long oil change intervals more important to you than engine protection? Those vehicle OEMs that pay for oil changes spec high detergent oils because their priority is long oil change intervals. More detergent means less slippery stuff. So maybe the OEM recommendation is best, but maybe not. Do your own research. Evaluate oils based on your priorities. Maybe you will come to the conclusion that the OEM recommendation is perfectly workable. Or maybe you won't. Viscosity is a measure of thickness. So a liquid with a high viscosity is thick and doesn't pour well. To remember this, I think of the phrase "molasses is thick and viscous". There is an optimum range of viscosity for every bearing design. Oil that is too thin (low viscosity) will form too thin of an oil cushion, more accurately referred to as a "hydrostatic wedge", in a hydrodynamic bearing (think.... crankshaft). Thick oil (high viscosity) can be bad flow if rates are important because thick oils flow poorly. Oil is sensitive to temperatures, particularly cold temperatures. That is to say, if you look at a chart of oil viscosity vs. temperature, you'll see a dramatic change between 0deg and 32deg, but not much change between 200deg and 232deg. Therefore when you are considering oil viscosity, focus more on cold behavior more than hot behavior. Oil with a viscosity that is borderline ok at 30deg might be entirely too thick at 0deg F. Oil that is borderline ok at 200deg F, will still be borderline ok at 230deg F. Good high temp shear #'s (HTHS) are important. This is a measure of how much hydrodynamic protection an oil provides at 100deg C. Generally high viscosity oils have better high temp shear #'s. Some particularly good oils, in fact, often have better high temp shear #'s then cheaper thicker competitors. Redline 5W20, for example, has better high temp shear #'s then most xW30's.That's one reason why you have to look beyond the viscosity grade of the oil. High Temp Shear #'s are important enough that one can more accurately judge an oil's ability to protect hydrodynamic bearings by comparing HTHS than viscosity. Using older BMW's as an example, instead of looking for an xW50, one could instead look for an HTHS >4. The most common anti-wear additive is ZDDP, but it's been reduced in most oils over the last two decades by successive oil certifications with lower limits. This was a result of a school of thought that says ZDDP damages catalytic convertors. There is some disagreement with this. Currently the limit for xW30 and lighter oils is 900 ppm (parts per million). There is some consensus that 1000-1400ppm might be better for our engines. ZDDP acts to protect bearing surfaces from damage. In contrast to the lubrication mode of creating a cushion between two metals, ZDDP provides an ablative layer on the steel to protect it from abrasion. This is particularly important for the top ends of engines (cam and rocker foot) that rely entirely on the anti-wear properties of an oil vs. a hydrodynamic bearing. Note that the government did not restricts the amount of ZDDP in xW40 and xW50. Most of those heavier oils have less ZDDP today because oil OEMs have chosen to do it that way for reasons of cost and simplicity. It's easier, for example, to have one "additive package" and add it to a whole line of oils, then it is to have 2 additive packages, one for light weight oils and another one that contains more ZDDP for heavier weight oils. So when xW40 and xW50 users blame the government for removing ZDDP, that's not correct. You can't rigorously compare ZDDP #'s between different oils. ZDDP and the detergent in an oil are antagonistic. That is to say, one oil might need lots of ZDDP because it has lots of calcium, a common detergent ingredient that will happily absorb ZDDP. Whereas another oil might have a detergent blend that has less calcium and less ZDDP. Both oils could have the same detergent value and anti-wear functionality. Therefore one must look deeper than simply comparing oil #1's 1300PPM (parts per million) ZDDP and oil #2's 1200PPM ZDDP. Many newer engines do not need as much anti-wear protection as older engines. Newer engines generally have more (smaller) valves, weaker valve springs, and have designed away some of the components that needed anti-wear additives for protection. The heavier valve springs of older engines, and the flat tappets of some old valve trains had high anti-wear requirements. Therefore for older engines, anti-wear additives like ZDDP can be important issues, but that is less true for newer engines. Newer API Certifications aren't necessarily better for engines. The newer API certifications were more oriented towards (perceived) pollution issues then engine life. E30 owner's manuals recommended 20W50 for high temp operation, but later changed that (high temp) recommendation to emphasize several xW40 oils (PDF). Editor's caution, this latter document, while short, requires some puzzling out. Don't blindly trust manufacturer data sheets. Oil blends change faster then websites and data sheets get updated. The only way to know for sure if your oil's chemistry is what you think it is, is oil analysis. Cam and follower lubrication. The top end of a motor has completely different lubrication requirements then the bottom end. Lubrication of the bottom end of a motor is a matter of maintaining a hydrostatic "oil wedge" between the rotating bearing surfaces. Lubrication of the top end is a product of the oil chemistry's ability to keep the follower and cam from gouging each other. The Aussie study below was a particularly good example of this. Note also that contact region surface area, spring pressure and lobe profiles all play major roles. Using Diesel oils. Diesel oils used to be popular among car owners because their certifications were slower to limit ZDDP. The more recent diesel certifications, however, do limit ZDDP which makes diesel oils less attractive to gas engine owners. Diesel oils and concerns re. foaming. Many oils that are marketed for diesel use are actually "mixed fleet" oils. This is significant because oils designed for diesel engines ONLY generally have less anti-foam ingredients. This is because the reduced RPM of diesel engines reduces the need for anti-foaming agents. So if you are inclined towards an oil marketed for diesel use, read the label and looked for a reference to "mixed fleet" use. A mixed fleet oil with a "CI+" certification can still be a nice fit for a gas engine that needs ZDDP. After all of this, what oil does Scott use? For the race car I generally use Brad Penn 20W40 or Redline 10W40 because they have excellent ZDDP #'s and terrific HTHS #'s. If they are not handy I'll use Valvoline VR1 (non-synthetic because cheaper. When I had the Ford F-150 I used Pennzoil Platinum 10W30. PP because it's well thought of by the tribologists at BITOG (www.BobIsTheOilGuy.com). 10W30 because Ford's recommendation re. 5W20 strikes me as likely artificially thin because of spec distortion by CAFE. For the Ford F-250 diesel I use Shell Rotella 10W40 based on recommendations at BITOG. Oil Change Interval. When I first started tracking a car in 2007, everyone in the forums used to say that it was necessary to change your oil after every couple of events. Some people seemed to feel strongly about changing their oil after every single event. I started out changing oil every couple events, then every 4 events, then 2x/yr, and I kept extending the oil change interval, doing an oil analysis (Blackstone Labs) each time. In Dec 2018 I changed the oil after almost 2yrs of racing, call it 50hrs on the track. And the analysis came back fine. Even the detergent level of the oil, as measured by the oil's acidity, was fine. So from now on I'm certainly not going to change the oil more often then every year, assuming normal track hours. A trick to extending your oil change interval is to add thicker oil then your original load. As your oil load ages, it's viscosity drops so the oil gets thinner. This is a result of contamination and molecular sheering (making long molecules shorter). So you can help restore the viscosity of your oil, make it thick again, by adding thicker oil. So if you normally run an xW40, do your occasional top-offs with xW50. If you can't get 50psi with hot oil at redline, then I'd add some thicker oil, unless you intentionally run thinnish oil. If you can't to 40psi with hot oil at redline, then I'd definitely add some thick oil.
Significant articles and forum threads Turbo Diesel Register: Oil myths (PDF) Turbo Diesel Register: New API certs aren't always better Oil for Performance Engines. This is a terrific article that is followed by a great FAQs section. It's oriented on Porsche air-cooled motors, but it's entirely applicable to other motors too. Selecting the right oil (PDF). This document was written with Corvairs in mind but contains lots of good information. Fuel Economy vs. Wear (PDF). Article discusses the latest trend in oils...Fuel economy at the expense of wear. Tests Aussie Oil Tests (PDF). Some of the oils tested aren't common in the US, but the test results really hammer home how different the results can be when the oil wedge fails. Oil chemistry matters. Turbo Diesel Register: 8 oils analyzed (first article in the series). Turbo Diesel Register: 21 oils analyzed (second article in the series). Blind studies. Short articles provide lots of nice background on what separates good oils from bad oils. Good, meaning your engine will last longer, not good means latest certifications. Keep in mind that the oils are being analyzed as diesel oils, not oils for gasoline engines. Diesel oils have 2-3X as much detergent as gas oils, so you have to account for that as you consider how the various oils were rated. If a couple oils did poorly because of low detergent content, they might be excellent oils for gasoline engines. Oils on the dyno (PDF). The results are not what you would expect.
Specs Redline Oil Specs (PDF) Valvoline VR-1 Specs (PDF). Note how the heavier oil has significantly more ZDDP than the lighter oil. Valvoline defends Street Legal VR-1 for high performance engines requiring ZDDP.
ZDDP Turbo Diesel Register: ZDDP (PDF) A parts vender's take on ZDDP and cams. Downward trend in ZDDP in modern certifications.
Background articles and info. Internal Combustion Engine Lubrication (PDF). This is the most concise article in this section. Hydrodynamic Bearings, an article from Race Technology Magazine. BobIsTheOilGuy.com. Link to top of forums. BITOG is by far the best oil info resource on the net. Motor Oil 101, BITOG Lubrication Tribology & Motorsport. Analysis of lubrication and power loss in a typical European motor vs. a Formula 1 motor. |
