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Kevin in NJ · 08-15-2012, 09:18 PM

Ya at 500 miles you are throwing away good oil.
Based what I have read from oil engineers that have written on the subject here are the issues you need to consider about oils (this applies to all cars).

Oil when the A was built was poorly refined and had little or no additives to keep it stable and not have bad chemicals build up in the oil. One example is when the moisture from condensate mixes with sulfur compounds formed durning combustion to make sulfuric acid. I have seen holes in the oil pan from the acid.

So you have two or three issues to think about to determine when you really need to change the oil.
First, when have the minerals that make lubrication broken down. These days it takes quite a while unless you have real high temps- which the A just will not make. Synthetics go a REAL long time and supposedly never break down. So this is not a reason to change oil in the A.
Second, when the additives have worn out. There are only so many molecules per volume of new oil that can lock down the bad chemicals. When you run out then the bad stuff will start to build up. I pointed out about the moisture and acid. This is something that happens even with the car sitting. You run the car it makes the sulfur compounds. Hopefully you got the engine hot enough and it burned off the water laying around. Then you put the car away. While the car is sitting the temps change from day to night. When the metal is cool and the air warms up the moisture in the air will condense out. Over the months that you do not drive the car this builds up in the engine. Well you can see. If you are using a compression ignition oil (diesel engine) they tend to have more additives to prevent the sulfur build up.
Third, dirt in the engine. We are not always talking the dirt from the road. The particulate build up from combustion as well as what you get from the road. These are small particles that are kept in suspension by detergents and come out when you change the oil. The build up is worse when driving in harsh environments, city driving is more harsh then country driving.

The 500 mile numbers are remnants of the days when crappy oil and bad roads were the rule.
That is not today.
Be nice to the environment and your pocket book and go longer between changes.

08-15-2012, 09:18 PM	#4
Kevin in NJ Senior Member Join Date: May 2010 Location: South East NJ Posts: 3,398	Re: Oil changes with filter Ya at 500 miles you are throwing away good oil. Based what I have read from oil engineers that have written on the subject here are the issues you need to consider about oils (this applies to all cars). Oil when the A was built was poorly refined and had little or no additives to keep it stable and not have bad chemicals build up in the oil. One example is when the moisture from condensate mixes with sulfur compounds formed durning combustion to make sulfuric acid. I have seen holes in the oil pan from the acid. So you have two or three issues to think about to determine when you really need to change the oil. First, when have the minerals that make lubrication broken down. These days it takes quite a while unless you have real high temps- which the A just will not make. Synthetics go a REAL long time and supposedly never break down. So this is not a reason to change oil in the A. Second, when the additives have worn out. There are only so many molecules per volume of new oil that can lock down the bad chemicals. When you run out then the bad stuff will start to build up. I pointed out about the moisture and acid. This is something that happens even with the car sitting. You run the car it makes the sulfur compounds. Hopefully you got the engine hot enough and it burned off the water laying around. Then you put the car away. While the car is sitting the temps change from day to night. When the metal is cool and the air warms up the moisture in the air will condense out. Over the months that you do not drive the car this builds up in the engine. Well you can see. If you are using a compression ignition oil (diesel engine) they tend to have more additives to prevent the sulfur build up. Third, dirt in the engine. We are not always talking the dirt from the road. The particulate build up from combustion as well as what you get from the road. These are small particles that are kept in suspension by detergents and come out when you change the oil. The build up is worse when driving in harsh environments, city driving is more harsh then country driving. The 500 mile numbers are remnants of the days when crappy oil and bad roads were the rule. That is not today. Be nice to the environment and your pocket book and go longer between changes.