Gtr Performance Q's

[RichyR32GTR]

A little on Motor Oils for you all.

The way that oil viscosity is referred to is by its weight. In this case, "weight" refers to the thickness of the oil and is usually measured with a Zahn cup. Any liquid has some viscosity and that viscosity changes depending on its temperature. Usually, viscosity (thickness) decreases as temperature increases. This also is true of engine oil. Engines need a thin oil at startup, so that it can get to the engine components quickly, but it needs a thicker oil when the engine is hot because a thin oil becomes too thin. This is why engine oils are supplied as dual-grade weights. When you see 10W-30 on an oil container, it means that it acts like 10 weight oil when it is cold (the "W" means winter, say -10^C), but acts like 30 weight oil when hot (100^C). This is not to say that it is actually thicker when it is hot. Hot 30 weight oil is thinner than cold 10 weight oil. Even so, it still helps provide the benefits of both types of oil depending on its temperature. So 0W-30 oil acts like 0 weight oil when cold, but maintains a 30 weight viscosity when hot. Think of it this way: when your engine is hot, there is basically no difference between 0W-30, 5W-30, and 10W-30 oil. They are all acting like 30 weight oil at this point. It's at cold startup, when almost all engine wear occurs, that the viscosity is different. The 0 weight oil will get to the engine components quicker than the 10 weight oil, but in reality cold 0 weight oil is still thicker than hot 30 weight oil. On the other hand when the engine is cold, there is no difference between 10W-30 and 10W-40 oil. However when the engine is hot, the 10W-40 oil is thicker than the 10W-30. This is why single-grade oils are very bad. Straight 30 weight oil is way too thick when cold to properly lubricate the engine. The only way to use single weight oil is to have an oil pan heater to bring the oil up to operating temperature (about 140^F or 60^C) before the engine is ever started. If you simply must use it, this type of oil should only be used in race engines with pan heaters.

As far as what oil viscosity is best, it depends who you ask. The fact is that engine oil maintains its viscosity better than ever and synthetics maintain it the best. In my opinion, the best viscosity for all weather is 5W-30. The reason is that both 5W-30 and 10W-30 breakdown at about the same point. Lighter oil can get into places that the heavier oil cannot and will get there more quickly, even when cold, so why go heavier? The only reason would be leaks. If you have oil leaks, a heavy oil will go through them more slowly. That is why you can buy "No-Smoke", which is basically sludge to thicken your oil. If your engine is sealed well, feel free to try a 0W-30 oil. If that "0" really makes you nervous, stick with 5W-30. 10W-30 is unnecessarily thick when cold.

THE method of classifying engine oil is complicated to the uninitiated. Unfortunately, there are as many differences in the performance of the different oils sold, as there are classifications.

Engine oils cleanse, cool and lubricate. The ideal oil maintains its cleansing, cooling and lubrication properties in-between oil changes, although this is seldom ever achieved.

The two main engine oil specifications that we should note are the SAE viscosity and the API classification. Oil viscosity is an indicator of its ability to flow, that is, how liquid it is. The higher the viscosity, the heavier or thicker the oil.

The viscous property of any liquid is highly dependent on temperature – oil flows much more easily at higher temperatures. It’s very important to remember this when determining which oil to use in a specific application, and the expected ambient temperature or range of temperatures.

Traditionally, viscous oils (with high SAE numbers) are suitable for use in high temperature applications, and vice versa.

But most modern multi-grade oils are blended to operate over a wide range of temperatures, from low winter temperatures right up to the high temperatures found in the tropics.

The API or ‘S’ classification addresses issues like deposit control, oxidation, corrosion, rust and wear.

As oils blends improve, this classification is constantly updated. Hence, oil with SC classification supercedes SD oil.

The latest classification is SM. It was introduced in November 2004 to provide better oxidation resistance, improved deposit and wear protection, and better low temperature performance.

Synthetics can take up to 450 degrees F. or higher. This makes synthetics well-suited for turbo applications as well as high rpm and high output engine applications.

Better low temperature performance. Synthetics flow freely at subzero temperatures, pouring easily at -40 or -50 degrees F. where ordinary oils turn to molasses. This makes for easier cold starts and provides faster upper valvetrain lubrication during the first critical moments when most engine wear occurs.

With regards to turbos, the manufacturers recommended oil weights are chosen specifically for that engine and the turbos are designed around this to make sure that the oil passages are big enough for enough oil to flow at startup to prevent bearing wear/seizure. I takes only a matter of minutes for bearings to start failing when there is not enough oil due to the speeds they spin at. When a turbo is hot the same principle applies. The oil must be thin enough for the oil to flow adequately, yet thick enough to have effective heat transfer and lubrication properties. If it's too thin you have oil film shear.

Basically when choosing oil, always follow the manufacturer's recommendation. When your car is getting older (more worn) choose an oil that has a slightly thicker "high temperature" viscosity than recommended.

Damn!! the more i read the more complicated it gets.. going to bed.. my head hurts.

Hope this shines a little light.