Best oil for a high mileage carrera
- Thread starter Guest
- Start date
Martin Perry
New member
I'm no technical wizz, but have heard that fully synthetic oil is a bit on the thin side for 911 engines, and they prefer a semi-synthetic.
Martin
Martin
oilman
New member
It depends really on whether you wish to upgrade to a synthetic or not but there are advantages to doing so.
For a car of this age, 15w-50 or 10w-50 is a good viscosity. What product you use depends on your personal preference but would suggest Mobil 1 or Silkolene are good ones to start with.
You will get many benefits from fully synthetic so long as the engine is in good condition to start with as they are far more superior lubricants than mineral oils. If the car is used for spirited driving or occasional trackdays then definately go the "true" synthetic route.
FYI, synthetics can be any viscosity you like so thickness/thinness does not come into the equation.
Any further questions, please ask, I'm here to help.
Cheers
Simon
For a car of this age, 15w-50 or 10w-50 is a good viscosity. What product you use depends on your personal preference but would suggest Mobil 1 or Silkolene are good ones to start with.
You will get many benefits from fully synthetic so long as the engine is in good condition to start with as they are far more superior lubricants than mineral oils. If the car is used for spirited driving or occasional trackdays then definately go the "true" synthetic route.
FYI, synthetics can be any viscosity you like so thickness/thinness does not come into the equation.
Any further questions, please ask, I'm here to help.
Cheers
Simon
Martin Perry
New member
Simon
I'm on a learning curve here. I note that synthetic oil can be of any viscosity. How does the classification work, or in other words waht do the numbers actually mean?
Martin
I'm on a learning curve here. I note that synthetic oil can be of any viscosity. How does the classification work, or in other words waht do the numbers actually mean?
Martin
oilman
New member
OK, you asked - Here goes!
What is this thing called viscosity?
It's written on every can of oil and it's the most important visible characteristic of an oil. The viscosity of an oil tells you how it reacts in certain circumstances and how it performs as a lubricant. When a oil is subjected to external forces, it resists flow due to internal molecular friction and viscosity is the measure of that internal friction. Viscosity is also commonly referred to as the measurement of the oils resistance to flow.
There are two methods of viewing an oils resistance to flow. Firstly there is Kinematic Viscosity which is expressed as units indicating the flow of volume over a period of time and this is measured in centistokes (cSt). An oils viscosity can also be viewed by measured resistance. This is known as Apparent Viscosity and it is measured in centipoises (cP).
However in the real world an oils viscosity is also referred to in such terms as thin, light and low etc. This suggests that the oil flows or circulates more easily. Conversly, terms such as heavy and high etc suggest the fluid has a stronger resistance to flow.
The reason for viscosity being so important is because it is directly related to the oils load-carrying ability - The greater an oils viscosity, the greater the loads that it can withstand. (It must be added when new not over a period of time as all oils "shear down" with use)
An oil must be capable of separating the moving parts in your engine at the operating temperature. On the basis that an oils viscosity is related to its load carrying ability, you could be fooled into thinking that "thicker" oils are better at lubricating but, you'd be wrong in this assumption. The fact is that in the wrong application a high viscosity oil can be just as damaging as using a low viscosity oil.
The use of an oil that's too "thin" can cause metal-to-metal contact, poor sealing and increased oil consumption and conversely, an oil that's too "thick" can cause increased friction, reduced energy efficiency, higher operating temperatures, and poor cold starts in cold temperatures.
It is very important that you select the correct oil, not too "light" or too "heavy" and your Owners Handbook is a very good place to start as it lists the temperatures and options.
Oils thicken at low temperatures and thin as the temperature increases. The actual rate of change is indicated by their viscosity index (this number normally listed on the oils technical data sheet indicates the degree of change in viscosity of an oil within a temperature range, currently 40-100 degrees centigrade)
An oil with a high viscosity index, will normally behave similarly at these two temperatures but an oil with a low viscosity index will behave quite differently. It will become very fluid, thin and pour easily at high temperatures. A higher index is better!
Multi-grade oils are designed to perform at high and low temperatures by adding polymers to a base oil (5w,10w, 15w etc) which are heat sensitive and "uncoil" to maintain the higher viscosity sae 30,40,50 etc. This means that the oil can be used "all year round" rather than using different oils for summer and winter.
It is important to understand that the selection of the correct oil for your car is not just guesswork, you must consider the temperatures at which you need the oil to operate a 0w, 5w oil is better for cold starts as the oil circulates more easily when it's cold and is able to flow around the engine more easily and quickly, offering protection at the critical moments following cold engine start-up. These oils are also known to give better fuel economy and engine performance.
Finally, all oils "shear" or thin down with use and this means that an oil that started life as a 10w-40 will with use become a 10w-20. The period of time this takes depends on the type and quality of the oil. The most "shear stable" oils are proper Synthetics, either PAO (Poly Alph Olefins) or Esters which have very high thermal stability. They are in general of the more expensive variety but last longer and give the best levels of protection.
Hope this explains
Cheers
Simon
What is this thing called viscosity?
It's written on every can of oil and it's the most important visible characteristic of an oil. The viscosity of an oil tells you how it reacts in certain circumstances and how it performs as a lubricant. When a oil is subjected to external forces, it resists flow due to internal molecular friction and viscosity is the measure of that internal friction. Viscosity is also commonly referred to as the measurement of the oils resistance to flow.
There are two methods of viewing an oils resistance to flow. Firstly there is Kinematic Viscosity which is expressed as units indicating the flow of volume over a period of time and this is measured in centistokes (cSt). An oils viscosity can also be viewed by measured resistance. This is known as Apparent Viscosity and it is measured in centipoises (cP).
However in the real world an oils viscosity is also referred to in such terms as thin, light and low etc. This suggests that the oil flows or circulates more easily. Conversly, terms such as heavy and high etc suggest the fluid has a stronger resistance to flow.
The reason for viscosity being so important is because it is directly related to the oils load-carrying ability - The greater an oils viscosity, the greater the loads that it can withstand. (It must be added when new not over a period of time as all oils "shear down" with use)
An oil must be capable of separating the moving parts in your engine at the operating temperature. On the basis that an oils viscosity is related to its load carrying ability, you could be fooled into thinking that "thicker" oils are better at lubricating but, you'd be wrong in this assumption. The fact is that in the wrong application a high viscosity oil can be just as damaging as using a low viscosity oil.
The use of an oil that's too "thin" can cause metal-to-metal contact, poor sealing and increased oil consumption and conversely, an oil that's too "thick" can cause increased friction, reduced energy efficiency, higher operating temperatures, and poor cold starts in cold temperatures.
It is very important that you select the correct oil, not too "light" or too "heavy" and your Owners Handbook is a very good place to start as it lists the temperatures and options.
Oils thicken at low temperatures and thin as the temperature increases. The actual rate of change is indicated by their viscosity index (this number normally listed on the oils technical data sheet indicates the degree of change in viscosity of an oil within a temperature range, currently 40-100 degrees centigrade)
An oil with a high viscosity index, will normally behave similarly at these two temperatures but an oil with a low viscosity index will behave quite differently. It will become very fluid, thin and pour easily at high temperatures. A higher index is better!
Multi-grade oils are designed to perform at high and low temperatures by adding polymers to a base oil (5w,10w, 15w etc) which are heat sensitive and "uncoil" to maintain the higher viscosity sae 30,40,50 etc. This means that the oil can be used "all year round" rather than using different oils for summer and winter.
It is important to understand that the selection of the correct oil for your car is not just guesswork, you must consider the temperatures at which you need the oil to operate a 0w, 5w oil is better for cold starts as the oil circulates more easily when it's cold and is able to flow around the engine more easily and quickly, offering protection at the critical moments following cold engine start-up. These oils are also known to give better fuel economy and engine performance.
Finally, all oils "shear" or thin down with use and this means that an oil that started life as a 10w-40 will with use become a 10w-20. The period of time this takes depends on the type and quality of the oil. The most "shear stable" oils are proper Synthetics, either PAO (Poly Alph Olefins) or Esters which have very high thermal stability. They are in general of the more expensive variety but last longer and give the best levels of protection.
Hope this explains
Cheers
Simon
oilman
New member
Just a thought, maybe this is useful too[
]
Surely the thicker the oil the better!
This isn't always true - even when using a petroleum oil. Although it is true that heavier viscosity oils (which are generally thought of as being thicker) will hold up better under heavy loads and high temperatures, this doesn't necessarily make them a better choice for all applications.
On many newer vehicles only 0w-40, 5w40 or 10w40 engine oils are recommended by the manufacturer. If you choose to use a higher viscosity oil than what is recommended, at the very least you are likely to reduce performance of the engine. Fuel economy will likely go down and engine performance will drop.
In the winter months it is highly recommended that you not use a heavier grade oil than what is recommended by the manufacturer. In cold start conditions you could very well be causing more engine wear than when using a lighter viscosity oil. In the summer months, going to a heavier grade is less of an issue, but there are still some things to be aware of.
Moving one grade up from the recommended viscosity is not likely to cause any problems (say from a 10w40 to a 10w50 oil). The differences in pumping and flow resitance will be slight. Although, efficiency of the engine will decrease, the oil will likely still flow adequately through the engine to maintain proper protection. However, it will not likely protect any better than the lighter weight oil recommended by the manufacturer.
Moving two grades up from the recommended viscosity (say 10w40 to 10w-60) is a little more extreme and could cause long term engine damage if not short term. Although the oil will still probably flow ok through the engine, it is a heavier visocosity oil. As such it will be more difficult to pump the oil through the engine. More friction will be present than with a lighter viscosity oil. More friction will be present than with a lighter viscosity oil. More friction means more heat. In other words, by going to a thicker oil in the summer months, you may actually be causing more heat build-up within the engine. You'll still be providing adequate protection from metal to metal contact in the engine by going with a high viscosity, but the higher viscosity will raise engine temperatures.
In the short run, this is no big deal. However, over the long term, when engine components are run at higher temperatures, they WILL wear out more quickly. As such, if you intend on keeping the vehicle for awhile, keep this in mind if you're considering using a heavier weight oil than the manufacturer recommends.
The best advice is to is to stay away from viscosity grades that are not mentioned in your owner's manual or ask me![]
Cheers
Simon
]Surely the thicker the oil the better!
This isn't always true - even when using a petroleum oil. Although it is true that heavier viscosity oils (which are generally thought of as being thicker) will hold up better under heavy loads and high temperatures, this doesn't necessarily make them a better choice for all applications.
On many newer vehicles only 0w-40, 5w40 or 10w40 engine oils are recommended by the manufacturer. If you choose to use a higher viscosity oil than what is recommended, at the very least you are likely to reduce performance of the engine. Fuel economy will likely go down and engine performance will drop.
In the winter months it is highly recommended that you not use a heavier grade oil than what is recommended by the manufacturer. In cold start conditions you could very well be causing more engine wear than when using a lighter viscosity oil. In the summer months, going to a heavier grade is less of an issue, but there are still some things to be aware of.
Moving one grade up from the recommended viscosity is not likely to cause any problems (say from a 10w40 to a 10w50 oil). The differences in pumping and flow resitance will be slight. Although, efficiency of the engine will decrease, the oil will likely still flow adequately through the engine to maintain proper protection. However, it will not likely protect any better than the lighter weight oil recommended by the manufacturer.
Moving two grades up from the recommended viscosity (say 10w40 to 10w-60) is a little more extreme and could cause long term engine damage if not short term. Although the oil will still probably flow ok through the engine, it is a heavier visocosity oil. As such it will be more difficult to pump the oil through the engine. More friction will be present than with a lighter viscosity oil. More friction will be present than with a lighter viscosity oil. More friction means more heat. In other words, by going to a thicker oil in the summer months, you may actually be causing more heat build-up within the engine. You'll still be providing adequate protection from metal to metal contact in the engine by going with a high viscosity, but the higher viscosity will raise engine temperatures.
In the short run, this is no big deal. However, over the long term, when engine components are run at higher temperatures, they WILL wear out more quickly. As such, if you intend on keeping the vehicle for awhile, keep this in mind if you're considering using a heavier weight oil than the manufacturer recommends.
The best advice is to is to stay away from viscosity grades that are not mentioned in your owner's manual or ask me![
]Cheers
Simon
Guest
New member
Thanks for the comments, was thinking of both the oils mentioned,i have un mobil 1 on sierra and escort cosworths and found it did find leaks on old higher mileage engines, so then considered magnetec. The porsche has covered 158,000 miles and i believe the engine has never been apart so is probably due for a rebuild and the old owner maintained the car himself and I can't get in touch with him. (Brought the car as a part ex from a local dealer). I will read through the comments when I have a bit more time and will let you know you what I have put in the car and how it works.
Thanks for your help.
Thanks for your help.
Guest
New member
Steve and Simon,
Don't assume that a motor with 158k on it needs work done to it. The previous owner could have been very carefull and loving to things like tappets and so on.
Simon,
whats your views on a by-pass oil filter, ie,
http://oilguard.com
Their price is quite good, and they offer a oil analysis service ( I know there are companies in UK who do likewise)
What do you think?
[]
Don't assume that a motor with 158k on it needs work done to it. The previous owner could have been very carefull and loving to things like tappets and so on.
Simon,
whats your views on a by-pass oil filter, ie,
http://oilguard.com
Their price is quite good, and they offer a oil analysis service ( I know there are companies in UK who do likewise)
What do you think?
[
]
oilman
New member
Well, semi-syn for trackdays would not be my recommendation as you need a "shear stable" oil in this environment, this is more important than the viscosity itself!
If the oil is not "shear stable" then it will break down and will become a thinner oil more quickly unless changed very frequently to avoid the risk of this happening.
Semi-synths are always "hydrocracked" or "molecularly modified" mineral oils, petroleum based, they are not "pure synthetics".
Because petroleum oils are made with light weight basestocks to begin with, they tend to burn off easily in high temperature conditions which causes deposit formation and oil consumption.
As a result of excessive oil burning and susceptibility to shearing (as well as other factors) petroleum oils must be changed more frequently than synthetics.
Not all multi-viscosity oils shear back so easily. True synthetic oils (PAO's and Esters) contain basically no waxy contamination to cause crystallization and oil thickening at cold temperatures. In addition, synthetic basestocks do not thin out very much as temperatures increase. So, pour point depressants are unnecessary and higher viscosity basestock fluids can be used which will still meet the "W" requirements for pumpability.
Hence, little or no VI improver additive would need to be used to meet the sae 30, 40 or 50 classification while still meeting 0W or 5W requirements.
The end result is that very little shearing occurs within true synthetic oils because they are not "propped up" with viscosity index improvers. There simply is no place to shear back to. In fact, this is easy to prove by just comparing synthetic and petroleum oils of the same grade.
Synthetics will generally have significantly higher HT/HS numbers. Of course, the obvious result is that your oil remains "in grade" for a much longer period of time for better engine protection and longer oil life
Cheers
Simon
If the oil is not "shear stable" then it will break down and will become a thinner oil more quickly unless changed very frequently to avoid the risk of this happening.
Semi-synths are always "hydrocracked" or "molecularly modified" mineral oils, petroleum based, they are not "pure synthetics".
Because petroleum oils are made with light weight basestocks to begin with, they tend to burn off easily in high temperature conditions which causes deposit formation and oil consumption.
As a result of excessive oil burning and susceptibility to shearing (as well as other factors) petroleum oils must be changed more frequently than synthetics.
Not all multi-viscosity oils shear back so easily. True synthetic oils (PAO's and Esters) contain basically no waxy contamination to cause crystallization and oil thickening at cold temperatures. In addition, synthetic basestocks do not thin out very much as temperatures increase. So, pour point depressants are unnecessary and higher viscosity basestock fluids can be used which will still meet the "W" requirements for pumpability.
Hence, little or no VI improver additive would need to be used to meet the sae 30, 40 or 50 classification while still meeting 0W or 5W requirements.
The end result is that very little shearing occurs within true synthetic oils because they are not "propped up" with viscosity index improvers. There simply is no place to shear back to. In fact, this is easy to prove by just comparing synthetic and petroleum oils of the same grade.
Synthetics will generally have significantly higher HT/HS numbers. Of course, the obvious result is that your oil remains "in grade" for a much longer period of time for better engine protection and longer oil life
Cheers
Simon
Posts made and opinions expressed are those of the individual forum members
Use of the Forum is subject to the Terms and Conditions
