Använd rätt olja, dom flesta äldre USA motorena skall ha hög zink 10W-30 vissa 10W-40 nästan aldrig 20W-50 (som är för trög).
Lite info från AMSOIL.

What is the difference between synthetic and conventional oil?

Answer: Motor oil, whether synthetic or petroleum-based, consists of molecular chains of hydrogen and carbon atoms, referred to as hydrocarbons. Petroleum crude oil is a thick, highly flammable dark-brown or greenish liquid with high energy density. Many contaminating elements exist in this complex mixture of hydrocarbons, including sulfur, nitrogen, oxygen and metal components such as nickel or vanadium. Petroleum crude oil is the raw material used for a wide variety of petrochemicals, including solvents, fertilizers, plastics and lubricants.

The oil refining process separates the various types of molecules in the oil by weight, resulting in a concentrated batch suitable for manufacturing products such as gasoline, LPG, kerosene or lubricant base oils. The chemical composition of conventional motor oil can vary substantially depending on the raw crude oil refining process.

While petroleum base oils are refined, synthetic base oils are manufactured and can achieve a higher performance level. Synthetic oil is chemically engineered for a certain molecular composition with a tailored and uniform structure. Such fine-tuned control over the final molecular composition of synthetic oils is the key to their superior performance properties. Designing molecular structures in a planned and orderly fashion results in molecules, and end-products, that are far more stable than their refined petroleum counterparts.

Will synthetic motor oils cause engines to leak oil?

Answer: No. Synthetic oils do not cause engines to leak oil. In fact, AMSOIL synthetic motor oil is fully compatible with modern seal materials and is properly formulated to condition seals, keeping them pliable to prevent leakage.

Why are AMSOIL synthetic motor oils capable of extended drain intervals?

Answer: AMSOIL synthetic motor oils are formulated using premium synthetic base oils, and the highest-quality additives, that provide extended-drain capabilities. AMSOIL synthetic motor oils achieve greater cleaning powers, while providing better equipment protection over longer oil drain intervals. The unique synthetic formulation and robust TBN retention of AMSOIL synthetic motor oils work to resist oxidation and neutralize the acids that shorten the service lives of other oils. Their characteristic resistance to high-temperature volatility (burn-off) helps reduce oil consumption, while maintaining viscosity over longer periods of time than other oils. Check the product data sheet for specific recommendations.

How do AMSOIL synthetic motor oils compare to other motor oils?

Answer: The importance of using good-quality oil in an engine cannot be overstated. AMSOIL synthetic motor oils consistently outperform conventional and other synthetic oils in virtually every category of performance, including wear protection, extreme high- and low-temperature performance, foam control, viscosity retention, rust and corrosion protection, volatility and fuel economy. While other brands may provide good performance in some of these areas, AMSOIL synthetic motor oils consistently perform at the top in every category. Drivers can have confidence knowing that AMSOIL synthetic motor oils provide maximum performance and protection.

I am considering replacing the petroleum oil with AMSOIL synthetic motor oil in an engine that has 50,000 miles on it. I have heard that synthetics might clean the engine and cause plugging of the oil filter and passageways. Is this true?

Answer: Absolutely not. Switching from petroleum oil to AMSOIL synthetic motor oil in routinely maintained vehicles will not cause clogged oil filters or passageways, regardless of mileage. Sludge, which is caused by poor-quality oil and neglected maintenance practices, would have to be present in significant amounts to plug oil filters and passageways. If an excessive amount of sludge is present in an engine, it is just a matter of time before oil filters and passageways clog, regardless of the installation of AMSOIL synthetic motor oil.

Why isn’t AMSOIL Dominator® Synthetic Racing Oil recommended for street-driven vehicles?

Answer: AMSOIL Dominator Synthetic Racing Oil is a premium-quality oil formulated for maximum protection in high-performance and racing applications. It is fortified with high levels of zinc and phosphorus, which are incompatible with catalytic converters common in today’s street-driven vehicles; therefore, Dominator Racing Oil does not carry API service classifications required by many standard passenger vehicles. However, Dominator Racing Oil is the ideal recommendation for street rods, muscle cars and other high-performance vehicles driven on the street.

What roles do additives play in motor oil performance?

Answer: Most lubricating oils have other chemicals added to improve the overall performance of the fluid. Chemical additives are used to enhance the beneficial properties of the base oil or to make up for oil deficiencies. For passenger car motor oils, base oil makes up 70 to 80 percent of the final product; the other 20 to 30 percent is comprised of additive chemistry.

Additives help lubricants stand up to extreme operating environments. Even the best base oil would not be able to protect as well against the effects of heat, shearing forces, chemical and water dilution, corrosion and wear particles. In short, additives make good base oils even better. They give good base oils the performance benefits consumers have come to expect, such as multi-grade performance, extended drain intervals and extreme-pressure performance.

Anti-wear Agents chemically react to form a film barrier that prevent metal-to-metal contact and wear.

Antioxidants reduce the tendency for oil to react with oxygen and reduce sludge buildup.

Dispersants help suspend and disperse contaminants in the oil to keep engine surfaces free of sludge and deposits. They fight the build-up of corrosive acids and are most efficient at controlling low-temperature deposits.

Contaminant Particles
Detergents help suspend and disperse contaminants in the oil to keep engine surfaces free of sludge and deposits. They are most efficient at controlling high-temperature deposits.

Extreme-Pressure Additives coat metal surfaces to help prevent close-contact components from seizing under extreme pressure. They are activated by high temperatures and high loads to react with the metal’s surface to form a sacrificial wear layer on components.

Foam Inhibitors reduce the surface tension of air bubbles and causes them to collapse.

Foam bubbles
Friction Modifiers can be used to give oil more 'slippery' characteristics. In engine oils, friction modifiers are used to increase the oil’s lubricity for the purpose of reducing friction and improving fuel economy.

Pour Point Depressants give high-viscosity oils good low-temperature properties. Pour point depressant polymers inhibit the formation of crystals to minimize low-temperature viscosity increase.

Rust & Corrosion Inhibitors form a protective barrier over component surfaces to seal out water and contaminants. While most rust and corrosion inhibitors work by forming a physical barrier, some rust inhibitors function by neutralizing acids.

Viscosity Index (VI) Improvers are long-chain polymers that help control the viscosity of multi-grade engine oils. They expand and contract as temperatures vary. High temperatures cause VI improvers to expand and reduce oil thinning; low temperatures cause VI improvers to contract and have little impact on oil viscosity. Viscosity Index Improver