Tuning tips: Choosing the correct grade of oil for your car.
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HDi fun
TC ModFather
Not bad at all. However, diesels don't burn cooler than petrols and the viscosity requirements are retty much the same.
The difference in oil requirements is to do with detergency and the oil's ability to retain sooty particles in suspension.
The difference in oil requirements is to do with detergency and the oil's ability to retain sooty particles in suspension.
That's interesting I thought that diesel combustion temperatures are significantly lower than petrol. My understanding was that turbos from petrols will work on diesels but not vice versa because of the heat issue.
HDi fun
TC ModFather
The turbos are much the same - presumably no-one's going to make one that only works on diesel engines because that's half the market gone. The old Garrett AiResearch T3 on my Peugeot was used on many petrol cars as well.
Turbo petrols probably do run hotter than turbo diesels and our NATASP Seat Ibiza D did run quite a lot cooler than a turbo diesel.
However, once you turbocharge a diesel engine the EGTs go up enormously, especially with the DPF's regeneration phase in action.
But the oil requirements are largely similar. Not so much because the engines are similar but because the oil makers are getting very clever at making multi-purpose oils.
Turbo petrols probably do run hotter than turbo diesels and our NATASP Seat Ibiza D did run quite a lot cooler than a turbo diesel.
However, once you turbocharge a diesel engine the EGTs go up enormously, especially with the DPF's regeneration phase in action.
But the oil requirements are largely similar. Not so much because the engines are similar but because the oil makers are getting very clever at making multi-purpose oils.
Interesting, thanks for the extra info, much appreciated.
Richard1
Torque Junkie
I think the idea behind the article is good, but since oil is my life, I'd like to clear up a few points, hoping you can leave a clearer picture for the average reader. It looks to be aimed at that level. Please don't take this wrong. There is a lot of lack of information out there. The campaign is necessary.
First: "If this is too thick the oil will not lubricate the engine properly with a resulting drop in oil pressure effectively creating dry spots and engine wear will be increased." Part of that is true, but oil too thick will cause TOO MUCH PRESSURE (not a drop in oil pressure). The pressure is measured by the resistance to flow between the pump and the bearings. If there is too much resistance, there are dry spots. It takes longer to get to the valve train and does not penetrate the bearings. In my tests a 20W-50 will take 4 seconds longer to reach the bearings than a 15W-40 in an engine Toyota says you can use either.
Second: "Thinner performance oils will never really reach their optimum viscosity in a standard low performance engine so again engine wear will be caused". All oils will reach there optimum viscosity if used in the right application with a thermostat. Each engine is designed for a specific viscosity at a specific temperature. I have some charts on my site, and a place for you to graph your own.
Third: "on some higher mileage engines we have noted that the thin synthetic oils seep through piston rings". The word Synthetic should be dropped here. A 5W-20 mineral oil and a 5W-20 synthetic oil have the same viscosity and will seep through the rings almost the same. If we were to split hairs, the mineral oil would seep through more, since it will shear down more. From my 15 years of experience in this, the word "synthetic" will be the take away for most people. The point could be made that "higher mileage" engines could benefit from slightly increasing viscosity from what was originally recommended (5W-20 to high mileage 5W-20 or 5W-30).
Forth: "It has been reported that use of incorrect oil types, especially in turbo applications (where oil is effectively baked in a hot turbo when the engine is shut off) can cause sludge to build up". Sludge is built up from running an engine too cold (short trips, too much idling, etc). The problem in turbos is low quality oil coking and forming deposits in the turbo bearings, causing them to wear or seize, as well as causing turbulence in the bearing, reducing its hydrodynamic properties. The comment of sludge is correct, but also creates insulation wherever it builds up, causing overheating, but this is not caused in the turbo.
Fifth: "There are (primarily) 3 types of oil: mineral oil, which is derived from refined crude oil, fully synthetic which is a blend of chemicals and polymers designed and engineered to lubricate the engine and then there is a semi synthetic which is a blend of the two." In reality, the mineral oil uses the polymers to cause a thin mineral oil to act like a thicker oil when hot. A 100% synthetic does not use polymers. A 5W-30 mineral oil is a 5W oil with polymers to make it act like a 30 at operating temps. A 5W-30 Synthetic is a 30W built to act as a 5W when it gets cold.
Sixth: "The second figure is to do with the working temperatures of the oil. A 40 is generally adequate for most engines operating at normal temperatures. On track days, heavy driving and in high performance engines, the heat build up can be extremely high. In this case using an oil with an SAE rating of 50 makes more sense." To a point this is true, but depends on the engine, the rpms generated and the temperature. Oil viscosity is determined by lateral force and speed. In a turbo or crankshaft bearing there is no lateral force, just velocity. The higher the velocity, the lower the viscosity should be. The same applies to the bearings. So if you go higher in basic viscosity then the operating temperature compensates, you create more resistance and heat, reducing performance. In my race cars with Honda Vtech engines that would normally run a 5W-30, I run a 5W-50. But all they do is race. No street use.
Seventh: "If you allow your engine to warm up properly before driving it hard you are giving the oil an opportunity to reach an effective operating temperature. This becomes even more important in winter months. Sadly though we see many drivers using high RPM on cold engines!" This is very true, just that idling an engine is just about as bad. The engine should be driven lightly, not hard, as soon as the oil starts circulating --- minimum 20 seconds, maximum 60 seconds. Then not driven hard, either high rpm or high torque until the temp is in the normal range.
As far as frequency of changes, I'm more comfortable with 6 months or 4000 miles for most oils, once a year or 10,000 miles for synthetics, but there are so many variables that I like to determine a base line with used oil analysis.
Most engines today are designed for viscosities between 8 and 12.5 cSt. here you can see where it takes a very hot running engine to drop a xW-50 oil into that range.
First: "If this is too thick the oil will not lubricate the engine properly with a resulting drop in oil pressure effectively creating dry spots and engine wear will be increased." Part of that is true, but oil too thick will cause TOO MUCH PRESSURE (not a drop in oil pressure). The pressure is measured by the resistance to flow between the pump and the bearings. If there is too much resistance, there are dry spots. It takes longer to get to the valve train and does not penetrate the bearings. In my tests a 20W-50 will take 4 seconds longer to reach the bearings than a 15W-40 in an engine Toyota says you can use either.
Second: "Thinner performance oils will never really reach their optimum viscosity in a standard low performance engine so again engine wear will be caused". All oils will reach there optimum viscosity if used in the right application with a thermostat. Each engine is designed for a specific viscosity at a specific temperature. I have some charts on my site, and a place for you to graph your own.
Third: "on some higher mileage engines we have noted that the thin synthetic oils seep through piston rings". The word Synthetic should be dropped here. A 5W-20 mineral oil and a 5W-20 synthetic oil have the same viscosity and will seep through the rings almost the same. If we were to split hairs, the mineral oil would seep through more, since it will shear down more. From my 15 years of experience in this, the word "synthetic" will be the take away for most people. The point could be made that "higher mileage" engines could benefit from slightly increasing viscosity from what was originally recommended (5W-20 to high mileage 5W-20 or 5W-30).
Forth: "It has been reported that use of incorrect oil types, especially in turbo applications (where oil is effectively baked in a hot turbo when the engine is shut off) can cause sludge to build up". Sludge is built up from running an engine too cold (short trips, too much idling, etc). The problem in turbos is low quality oil coking and forming deposits in the turbo bearings, causing them to wear or seize, as well as causing turbulence in the bearing, reducing its hydrodynamic properties. The comment of sludge is correct, but also creates insulation wherever it builds up, causing overheating, but this is not caused in the turbo.
Fifth: "There are (primarily) 3 types of oil: mineral oil, which is derived from refined crude oil, fully synthetic which is a blend of chemicals and polymers designed and engineered to lubricate the engine and then there is a semi synthetic which is a blend of the two." In reality, the mineral oil uses the polymers to cause a thin mineral oil to act like a thicker oil when hot. A 100% synthetic does not use polymers. A 5W-30 mineral oil is a 5W oil with polymers to make it act like a 30 at operating temps. A 5W-30 Synthetic is a 30W built to act as a 5W when it gets cold.
Sixth: "The second figure is to do with the working temperatures of the oil. A 40 is generally adequate for most engines operating at normal temperatures. On track days, heavy driving and in high performance engines, the heat build up can be extremely high. In this case using an oil with an SAE rating of 50 makes more sense." To a point this is true, but depends on the engine, the rpms generated and the temperature. Oil viscosity is determined by lateral force and speed. In a turbo or crankshaft bearing there is no lateral force, just velocity. The higher the velocity, the lower the viscosity should be. The same applies to the bearings. So if you go higher in basic viscosity then the operating temperature compensates, you create more resistance and heat, reducing performance. In my race cars with Honda Vtech engines that would normally run a 5W-30, I run a 5W-50. But all they do is race. No street use.
Seventh: "If you allow your engine to warm up properly before driving it hard you are giving the oil an opportunity to reach an effective operating temperature. This becomes even more important in winter months. Sadly though we see many drivers using high RPM on cold engines!" This is very true, just that idling an engine is just about as bad. The engine should be driven lightly, not hard, as soon as the oil starts circulating --- minimum 20 seconds, maximum 60 seconds. Then not driven hard, either high rpm or high torque until the temp is in the normal range.
As far as frequency of changes, I'm more comfortable with 6 months or 4000 miles for most oils, once a year or 10,000 miles for synthetics, but there are so many variables that I like to determine a base line with used oil analysis.
Most engines today are designed for viscosities between 8 and 12.5 cSt. here you can see where it takes a very hot running engine to drop a xW-50 oil into that range.
Thanks for the updates and I'll try and get the article updated today.
Richard1
Torque Junkie
For a lot of people a simple article like that is all they need and will read. If you want a link for those who want all the reasons behind this, you can link to this article that I wrote for the Corvair community where flat tappets (sliding) valve trains are important considerations.
http://www.widman.biz/Corvair/English/Links/Oil.html
Also, if you want to straighten out transmission oils, check this one out:
http://www.widman.biz/Corvair/English/Links/Transaxle.html
http://www.widman.biz/Corvair/English/Links/Oil.html
Also, if you want to straighten out transmission oils, check this one out:
http://www.widman.biz/Corvair/English/Links/Transaxle.html
HDi fun
TC ModFather
There's something to be said for using an oil which suits your ambient temperatures.
a 5w/60 oil will require more viscosity improvers than a 5w/30, for example.
Viscosity improvers take the form of long chain polymers which literally uncurl in response to temperature. This doesn't actually increase the viscosity but reduces the thinning effect of heat on a single weight base oil.
The VIs generally break down long before the base stock, especially so in the case of synthetic oils but then again fully synthetic oils are less dependent upon VIs.
So you need to consider many factors, not least of which is the engine manufacturers recommendations for your car, your climate and your operating conditions.
Basically, if you can get away with a quality 5w/30 synthetic then going for a 0w/60 will possibly introduce a weakness which need not be encountered.
As Richard1 has said, overly viscous oils can create a boundary layer film which will literally tear if the relative velocity of the surfaces is too high. They [needlessy viscous oils] can also cause excessive crankcase pressures which will force oil into places it should be going, like past the piston rings etc.
Many drivers make the mistake of thinking that thicker is always better. This is totally contrary to the truth.
All engine oils are, and have always been, designed upon a set of compromises, there is not yet the perfect engine lubricant.
Nor is there the perfect, frictionless, engine. If there was it would not require any fluid lubricant at all.
a 5w/60 oil will require more viscosity improvers than a 5w/30, for example.
Viscosity improvers take the form of long chain polymers which literally uncurl in response to temperature. This doesn't actually increase the viscosity but reduces the thinning effect of heat on a single weight base oil.
The VIs generally break down long before the base stock, especially so in the case of synthetic oils but then again fully synthetic oils are less dependent upon VIs.
So you need to consider many factors, not least of which is the engine manufacturers recommendations for your car, your climate and your operating conditions.
Basically, if you can get away with a quality 5w/30 synthetic then going for a 0w/60 will possibly introduce a weakness which need not be encountered.
As Richard1 has said, overly viscous oils can create a boundary layer film which will literally tear if the relative velocity of the surfaces is too high. They [needlessy viscous oils] can also cause excessive crankcase pressures which will force oil into places it should be going, like past the piston rings etc.
Many drivers make the mistake of thinking that thicker is always better. This is totally contrary to the truth.
All engine oils are, and have always been, designed upon a set of compromises, there is not yet the perfect engine lubricant.
Nor is there the perfect, frictionless, engine. If there was it would not require any fluid lubricant at all.
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