Oil Change Question
#8
04-07-2005, 01:07 AM
RE: Oil Change Question (COpied from Audi World Forum)
There have been so many posts about oil I feel compelled to write about this subject a bit to share some of my thoughts in one shot (or two). Oils have many purposes in an internal combustion engine. In addition to lubricating they clean, dissipate and reduce heat in both moving and non-moving engine parts. There are many brands and types of oil on the market and while many of these lower cost over the counter brands are ok in many day to day situations there are better oils out there. In fact many oils do not measure up to their advertised claims such as "Low Sludge", "Mechanics Choice" or "Fights Thermal Breakdown".
As oil is circulated through your engine it dissipates heat stored in the parts it contacts, it also lubricates and removes friction from all moving parts which include: bearings, seals, cylinder walls, valve train, (lifters cam lobes etc). This we all know but oil does some things we don't normally think of. Oil is very important in aiding piston ring sealing; there is a small amount of oil that is burned off in this process. Unless of course your engine has poor piston ring "seating" in which case it burns more oil. Oil is also key in valve spring cooling as these parts reside in a very hot and enclosed area of the engine.
The oiling system of most motors is very simple and this is good. There is an oil pan that forms a reservoir, an oil pump which forces oil through a filter (typically 10 to 20 microns...which is not that great) then through the engines oil galleys which lead it to various bearing surfaces. Oil capacity can be as little as 3 quarts in a 500cc motorcycle to over 14 quarts in a big truck. Pumps are gear, chain or belt (toothed) driven and can be of internal or external design with multiple pump set-ups in some engines. Some high performance engine unitizes a dry sump where the oil is stored in a separate tank with a dedicated pump to pull oil from the tank and another to pump oil into the tank. The advantage of a dry sump is less friction or windage caused by the crankshaft plowing through oil and reduced heat but perhaps most important is a constant supply of oil. In some cases a wet sump can go dry if enough G force is exerted on the vehicle as in a racing application. A good example of this is a motorcycle doing a wheelie where all the oil runs to the back of the crankcase and away from the oil pick up. Airplanes also would have a similar problem flying upside-down, thus the dry sump. In fact, just braking hard enough in some vehicles is all it takes to cause a lack on oil at the pick up (often baffles are used in wet sump engines to prevent this). Inside the oil pump is a pressure spring or a loaded ball that mechanically controls oil pressure. Oil pressure varies with engine speed up to the maximum pressure allowed by this mechanical control. Believe it or not most oil pumps are not high volume pumps because if they were the sumps would quickly be sucked dry with all the oil ending up in the cylinder heads. Typically the more oil the system moves the more horsepower it takes to do so. Also of note is the fact that higher oil pressure causes a slight horse power drain. This is why in the AMA 600 Super Sport class (an essentially stock racing class) all the top teams use is very trick and hard to detect , lower than stock oil pressure system. This systems pressure is not low enough to cause an oiling failure but low enough to pick up a small power gain. Along this line, the higher the oil viscosity, the more power it takes to pump the oil through the engine. Looking at racing again we see special synthetic 'zero weight' qualifying oil being used by Formula 1 teams (and Nascar) that our friends at Mobil have developed (I understand that certain F1 teams have their own formulations). Don't think this is going to extremes, not with one 800HP F1 engine completely used up in practice then thrown away. Well that's what a $330,000,000 budget will do (a top F1s teams annual budget).
Oil viscosity varies in a range for zero up to 90weight and beyond. There are 'straight weight' oils (straight 50 weight) and multi viscosity oils like 10W 40. In today's engines multi weight oils are the standard and there has been a trend towards lighter weight oils like 5w 30 where in the past 10w 40 was almost universal. Oils achieve this multi viscous nature by the use of long 'chain molecules' that unfold as they heat up. So they flow well at cold start up but don't thin to the point of film failure as temperatures rise. Oil temps as high as 275 degrees are normal and they can climb to 325 degrees at which point some oils begin to break down (synthetics are you best insurance against this). However there are flash points inside an engine were oil is subjected to extremely high temperature. Don't forget that combustion temp can reach 6000 degrees (hot enough to melt any metal in your engine- but that's another story). As we drive our oil begins to loose viscosity so a 10w 40 may become an 8w 30 over time. This happens by a process called 'shear down' where the long chain molecules are ground down into pieces. This is particularly troublesome in gearboxes, as meshing gear teeth are the prime crunchers of chain molecules. This is why motorcycles that use engine oil to lubricate their transmissions will never have the long oil change intervals we are seeing in autos. Automobile transmissions use separate oil for their gearboxes, typically something like straight 90weight-gear oil as an example. Many a home mechanic will wrongly assume that if 10w 40 is good 20w 50 is better for summer driving. This is not necessarily the case as heavier oil can reduce lubrication. This has to do with flow dynamics or lack there of in a heavier weight oil. All I'll say is follow the manufactures call out on the spec sheet.
As I said many times anyone that still believes that there is no benefit in using synthetic oils is simply uniformed. Good synthetic oils give you a horse power and mpg gain of between 1% and 3%. The lubricating qualities and slipperiness of synthetics are far superior to conventional oils and effectively extend engine life. Synthetics produce little or no residues and contaminants as compared to mineral-based oils. They have a much higher 'flash point' that allows them to dissipate heat better and lubricate better at extreme temperatures. They don't 'coke up' at high heat levels, which is good for a turbo charged car like the TT; think about the oil that lingers in the exhaust side of your turbo after shut off. These oils are also better in cold weather conditions due to their high flow characteristics at low temps (10% better than mineral based oils). A good analogy is to think of mineral based oils as an army made up of the general population; some solders are tall, some fat, some weak and some strong. In a synthetic oil army all solders are six feet tall and all are strong, an army of clones if you will. Just because you buy synthetic oil does not mean you have a 'good' synthetic. The good synthetics will give you up to a 3% increase in power (on a dyno pull) with a similar increase in gas mileage. My favorite synthetics are the Mobil 1 family of oils because they are readily available and because Mobil invented the stuff (I use 5W 30 but am looking at 0w 30). Back in the early 1960s the Navy asked Mobil to develop a lubricant that would not solidify. The problem was that their new carrier jets wheel-bearing grease was freezing solid at high altitude and upon landing the bearings would fail. Mobil came up with synthetic lubricants as the solution and the rest is history. Other good synthetic oil choices are Redline, Torco and Amsoil, the rest don't measure up on the dyno (no power increase).
There is a lot of debate over the oil change interval, which is now up to 15,000 on some maintenance schedules. First there is no argument that a synthetic oil can run longer between oil changes. But how long do you keep a synthetic in your engine, there is no simple answer but if you ask me I'll tell you 6000miles. While letting your oil go too long can do serious damage, you can't hurt your motor by changing oil frequently; you could change it every day with no ill effect. Regardless of how often you change oil you should check its level and top it off every week or with each fill up. The condition of an engine will bear on when you change oil as a motor that burns some oil will also have 'blow buy' and you will need to get these combustion contaminants out of the system. I have a collection of service manuals that go back as far as the 1940s and the 2000 to 3000 mile change interval was the norm then; oil, like motor technology has come a long way. This at least proves that Jiffy Lube is not responsible for the 3000-mile figure.
This is all for now, I still want to write about break-in oils (this is an amazingly complex subject), oil additives and changing your oil at home. JIM
As oil is circulated through your engine it dissipates heat stored in the parts it contacts, it also lubricates and removes friction from all moving parts which include: bearings, seals, cylinder walls, valve train, (lifters cam lobes etc). This we all know but oil does some things we don't normally think of. Oil is very important in aiding piston ring sealing; there is a small amount of oil that is burned off in this process. Unless of course your engine has poor piston ring "seating" in which case it burns more oil. Oil is also key in valve spring cooling as these parts reside in a very hot and enclosed area of the engine.
The oiling system of most motors is very simple and this is good. There is an oil pan that forms a reservoir, an oil pump which forces oil through a filter (typically 10 to 20 microns...which is not that great) then through the engines oil galleys which lead it to various bearing surfaces. Oil capacity can be as little as 3 quarts in a 500cc motorcycle to over 14 quarts in a big truck. Pumps are gear, chain or belt (toothed) driven and can be of internal or external design with multiple pump set-ups in some engines. Some high performance engine unitizes a dry sump where the oil is stored in a separate tank with a dedicated pump to pull oil from the tank and another to pump oil into the tank. The advantage of a dry sump is less friction or windage caused by the crankshaft plowing through oil and reduced heat but perhaps most important is a constant supply of oil. In some cases a wet sump can go dry if enough G force is exerted on the vehicle as in a racing application. A good example of this is a motorcycle doing a wheelie where all the oil runs to the back of the crankcase and away from the oil pick up. Airplanes also would have a similar problem flying upside-down, thus the dry sump. In fact, just braking hard enough in some vehicles is all it takes to cause a lack on oil at the pick up (often baffles are used in wet sump engines to prevent this). Inside the oil pump is a pressure spring or a loaded ball that mechanically controls oil pressure. Oil pressure varies with engine speed up to the maximum pressure allowed by this mechanical control. Believe it or not most oil pumps are not high volume pumps because if they were the sumps would quickly be sucked dry with all the oil ending up in the cylinder heads. Typically the more oil the system moves the more horsepower it takes to do so. Also of note is the fact that higher oil pressure causes a slight horse power drain. This is why in the AMA 600 Super Sport class (an essentially stock racing class) all the top teams use is very trick and hard to detect , lower than stock oil pressure system. This systems pressure is not low enough to cause an oiling failure but low enough to pick up a small power gain. Along this line, the higher the oil viscosity, the more power it takes to pump the oil through the engine. Looking at racing again we see special synthetic 'zero weight' qualifying oil being used by Formula 1 teams (and Nascar) that our friends at Mobil have developed (I understand that certain F1 teams have their own formulations). Don't think this is going to extremes, not with one 800HP F1 engine completely used up in practice then thrown away. Well that's what a $330,000,000 budget will do (a top F1s teams annual budget).
Oil viscosity varies in a range for zero up to 90weight and beyond. There are 'straight weight' oils (straight 50 weight) and multi viscosity oils like 10W 40. In today's engines multi weight oils are the standard and there has been a trend towards lighter weight oils like 5w 30 where in the past 10w 40 was almost universal. Oils achieve this multi viscous nature by the use of long 'chain molecules' that unfold as they heat up. So they flow well at cold start up but don't thin to the point of film failure as temperatures rise. Oil temps as high as 275 degrees are normal and they can climb to 325 degrees at which point some oils begin to break down (synthetics are you best insurance against this). However there are flash points inside an engine were oil is subjected to extremely high temperature. Don't forget that combustion temp can reach 6000 degrees (hot enough to melt any metal in your engine- but that's another story). As we drive our oil begins to loose viscosity so a 10w 40 may become an 8w 30 over time. This happens by a process called 'shear down' where the long chain molecules are ground down into pieces. This is particularly troublesome in gearboxes, as meshing gear teeth are the prime crunchers of chain molecules. This is why motorcycles that use engine oil to lubricate their transmissions will never have the long oil change intervals we are seeing in autos. Automobile transmissions use separate oil for their gearboxes, typically something like straight 90weight-gear oil as an example. Many a home mechanic will wrongly assume that if 10w 40 is good 20w 50 is better for summer driving. This is not necessarily the case as heavier oil can reduce lubrication. This has to do with flow dynamics or lack there of in a heavier weight oil. All I'll say is follow the manufactures call out on the spec sheet.
As I said many times anyone that still believes that there is no benefit in using synthetic oils is simply uniformed. Good synthetic oils give you a horse power and mpg gain of between 1% and 3%. The lubricating qualities and slipperiness of synthetics are far superior to conventional oils and effectively extend engine life. Synthetics produce little or no residues and contaminants as compared to mineral-based oils. They have a much higher 'flash point' that allows them to dissipate heat better and lubricate better at extreme temperatures. They don't 'coke up' at high heat levels, which is good for a turbo charged car like the TT; think about the oil that lingers in the exhaust side of your turbo after shut off. These oils are also better in cold weather conditions due to their high flow characteristics at low temps (10% better than mineral based oils). A good analogy is to think of mineral based oils as an army made up of the general population; some solders are tall, some fat, some weak and some strong. In a synthetic oil army all solders are six feet tall and all are strong, an army of clones if you will. Just because you buy synthetic oil does not mean you have a 'good' synthetic. The good synthetics will give you up to a 3% increase in power (on a dyno pull) with a similar increase in gas mileage. My favorite synthetics are the Mobil 1 family of oils because they are readily available and because Mobil invented the stuff (I use 5W 30 but am looking at 0w 30). Back in the early 1960s the Navy asked Mobil to develop a lubricant that would not solidify. The problem was that their new carrier jets wheel-bearing grease was freezing solid at high altitude and upon landing the bearings would fail. Mobil came up with synthetic lubricants as the solution and the rest is history. Other good synthetic oil choices are Redline, Torco and Amsoil, the rest don't measure up on the dyno (no power increase).
There is a lot of debate over the oil change interval, which is now up to 15,000 on some maintenance schedules. First there is no argument that a synthetic oil can run longer between oil changes. But how long do you keep a synthetic in your engine, there is no simple answer but if you ask me I'll tell you 6000miles. While letting your oil go too long can do serious damage, you can't hurt your motor by changing oil frequently; you could change it every day with no ill effect. Regardless of how often you change oil you should check its level and top it off every week or with each fill up. The condition of an engine will bear on when you change oil as a motor that burns some oil will also have 'blow buy' and you will need to get these combustion contaminants out of the system. I have a collection of service manuals that go back as far as the 1940s and the 2000 to 3000 mile change interval was the norm then; oil, like motor technology has come a long way. This at least proves that Jiffy Lube is not responsible for the 3000-mile figure.
This is all for now, I still want to write about break-in oils (this is an amazingly complex subject), oil additives and changing your oil at home. JIM
#9
05-13-2005, 03:21 PM
5.3qts?
Whoa, 5.3 qts would not be enough! Manual says 6.0 but most dealers recommend 6.2-6.3qts. A recent TSB stated 6.0qts as well.
Keep in mind the filter also ends up holding oil as well.
Most dealers I have called recommend 5W-30. I use Mobil 1. Some people use Mobil 1 European Formula 0W-40 with no ill effects. The A6 2.8 is pretty forgiving with the different blends its willing to accept. I always recommend synthetic. A recent audi tech took apart my friends 1.8T and was amazed at how 'clean' the engine parts were. Very little corrosion, no sludge, just a clean, well lubricated engine. He had been using Mobil 1 synthetic every since his first oil change. The stuff works!
Keep in mind the filter also ends up holding oil as well.
Most dealers I have called recommend 5W-30. I use Mobil 1. Some people use Mobil 1 European Formula 0W-40 with no ill effects. The A6 2.8 is pretty forgiving with the different blends its willing to accept. I always recommend synthetic. A recent audi tech took apart my friends 1.8T and was amazed at how 'clean' the engine parts were. Very little corrosion, no sludge, just a clean, well lubricated engine. He had been using Mobil 1 synthetic every since his first oil change. The stuff works!
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