Tuesday, March 25, 2014
OIL: The Good, The Bad, and The Swamp Sludge...
With todays' topic, we are going do dive into a bit of a slippery subject- engine oil and oil changes. We have been told for years that oil changes need to happen every 3000 miles, but why? All oils are slippery right, so is there really that much difference between oils and how they perform? I wish I could, in good conscience, say that whatever oil you pour into your engine is fine. I wish I could say that oil changes don't matter and it also doesn't matter what kind of filter you use, or how often you change it. Sorry, No can do.
Oil quality does matter, so does the filter quality. Cheap oils don't protect as well, plain and simple, and cheap filters will be another topic for later discussion.
First and foremost, the oil needs to protect the parts from ever making contact with each other. This is called film strength and is not related anymore to the idea of viscosity, or thickness of the oil. There is still the mistaken idea that a thicker oil will protect better. This is simply no longer true. Back in the old days of engine oil, oil companies were filtering the unwanted junk out of old dinosaurs and swamp sludge, then cracking the molecules to make oil from tarry goo. This system of filtering and cracking worked pretty well, but left contaminants in the oil, final consistency was highly variable and since the lubricants were actually diluted in waxes and random other hydrocarbon combinations, the friction coefficient was questionable and unreliable at best. In those days, a thicker oil would act as a cushion and even if it wasn't the best lubricant, it would still prevent the metal parts from grinding together... much. A thick oil simply cannot ooze or flow out of the way of the metal parts the way a thinner oil would. Viscosity came to equal film strength in the minds and hearts of gear heads everywhere. Unfortunately, a thicker oil is harder to pump which means lower fuel economy. Thicker oil will also cause slower build-up of oil pressure at cold start because it takes more time to move through the pump, filter and oil galleys. A cold start is when most of the damage to bearings and camshaft followers happen, starving them for oil longer by using a thicker oil makes no sens- once the metal is ground away, no amount of oil can make up for it. Time is the only function that really matters in cold-start situations- get oil in as fast as possible and stop the metal-to-metal contact and thus stop the wear. Pre-oilers are pricey, but can be worth it in some applications. I will do an article on pre-oilers soon...
Today, with the tech we have available, the idea of film strength being related to viscosity is simple fallacy. With newer lubricant engineering techniques, the idea that a 0w-20 oil can protect as well or in some cases better than a 20w-50 oil is being accepted more and more. Modern oil manufacturing has given us far superior technology for removing unwanted fossilized plesiosaur spleens and other yuck from our oil supply. We also have dedicated chemical labs building specialized additives like ZDDP and mineral ashes that make excellent lubricants. Oils today are much better at dealing with chemical attacks from acids inside the engine as well because the engineers are closing the molecular ends and removing reaction sites that can cause oil to break down and lose its lubricity.
Shear forces from fast moving metal parts literally tear oil molecules apart too. With modern technology, we have additives in oils consisting of special molecules that form round blobs that are easy to pump, but when subjected to severe shear forces, actually straighten out, interlock and increase viscosity and film strength instantly to protect moving parts. As soon as the shear forces are removed, the molecules change shape again and go back to a thin, easy flowing liquid. These molecule literally break and get torn apart in doing their job. After enough of the lubricative molecules break, get crushed or torn, have suffered chemical damage, or just lose the ability to protect the engine, it is time to remove them from service, and get new oil back in.
Inside the engine an oil is exposed to damaging abuse- physical, chemical and heat related. After- often before- 3000 miles, cheap oil wears out, breaks down, becomes contaminated and damaging in some cases- its time is up and cannot be allowed to remain in the engine. When the oil reaches this point it must be replaced. Yes synthetics last longer- we'll chat about synthetics later tho K?
Another consideration regarding oil changes- pre-filling the oil filter. Most shadetree, race, or fleet mechanics know what I am talking about here. This is one that I am kinda pissy about, I admit. I ALWAYS fill- or at least pre-wet, a filter before I install it. ALWAYS! A new filter is full of what? AIR. Not a great lubricant for metals, last time I checked. Oil changes are supposed to result in engine longevity, not ruining the engine by running it without oil until the pump primes and the filter can fills with oil to finally get oil to the bearings again. The practices of Blah-Mart or LubeGuys or any quickie oil change place result in faster engine death due to bad work habits by unsupervised and inexperienced first year mechanics screwing on dry filters and hurrying the process. I have asked several different lube shops over the years about it and none of them had ever heard of pre-filling oil filters. These shady shops make their money from quantity of clients, not quality of work. Do not let these shops change your oil- find a good trustworthy mechanic who knows this... or just do it yourself.
There I said it. I think we should all be doing our own oil changes. Its easy, and you know its done right- no drain plugs cross-threaded, no loose filters and no screwing on a dry oil filter. If your goal is to kill your engine quickly, let these folks change the oil often and screw on a dry filter every time.
OR, for much greater engine longevity... pour good oil into a good filter to, at minimum, pre-wet the filter media inside. Preferably though, fill it three times over the 5 minutes it takes for the oil to finish draining out of the engine. Its best that all the air bubbles come out before installing it. Don't forget to oil the o-ring on the top of the filter too.
K, hope that all makes sense. Til next time...