Engine oil

Shannonsider

I've had a look on the net and tried searching here but can't seem to find out what different engine oils are for (i.e. what all the different types actually mean).

For example, the difference between 4W40 and 10W30, semi or fully synthetic?

Anyone put it all in lay-man's terms?

Also, can a number of different oils be used to top-up an engine or does it have to be a specific recommended oil?

In layman's terms - use what the manufacturer recommends

biko

Generally don't mix oil (unless you know what you're doing).

Oil weight, or viscosity, refers to how thick or thin the oil is. The temperature requirements set for oil by the Society of Automotive Engineers (SAE) is 0 degrees F (low) and 210 degrees F (high).

Oils meeting the SAE's low temperature requirements have a "W" after the viscosity rating (example: 10W), and oils that meet the high ratings have no letter (example SAE 30). An oil is rated for viscosity by heating it to a specified temperature, and then allowing it to flow out of a specifically sized hole. Its viscosity rating is determined by the length of time it takes to flow out of the hole. If it flows quickly, it gets a low rating. If it flows slowly, it gets a high rating.

Engines need oil that is thin enough for cold starts, and thick enough when the engine is hot. Since oil gets thinner when heated, and thicker when cooled, most of us use what are called multi-grade, or multi-viscosity oils. These oils meet SAE specifications for the low temperature requirements of a light oil and the high temperature requirements of a heavy oil.

You will hear them referred to as multi-viscosity, all-season and all-weather oils. An example is a 10W-30 which is commonly found in stores. When choosing oil, always follow the manufacturer's recommendation.
http://www.autoeducation.com/autoshop101/oil-change.htm

Motor oil is designed to serve many different purposes within a cars engine. While the primary function is to simply lubricate all the moving parts and provide protection from wear and corrosion, it also is intended to keep the engine cool and free from small pieces of debris.

Conventional motor oils are made from crude oil which has been is pumped from the ground and then processed in a refinery to create a base oil. Additives are then mixed into the base oil to change the viscosity, protection properties and heat breakdown levels of the oil.

Synthetic oil is also created in a similar manner to a conventional engine oil, using a base oil combined with a series of additives. The difference lies in the fact that synthetic motor oils are created utilizing a specially "synthesized" base oil where the size of the oil molecules are all of an ideal weight and of a consistent size. While a conventional motor oil, despite the refining processes, is made up of different molecule sizes which are mixed together, along with various waxes and impurities, a fully synthetic oil is made to provide a much purer base oil, with less waxes and with a uniform ideal particle size to help increase the oils viscosity level. Added to this ideal base oil is a combination of more technically sophisticated additives than are used with the conventional oils.

The additives which are used in the production of synthetic oils can help to create an extremely stable engine oil which will sustain the correct viscosity levels across a large range of temperatures and which will flow properly at lower temperatures when compared against conventional oils. Additional friction inhibitors which are activated at lower temperatures than those of conventional oils, are generally included in synthetic motor oils, to provide improved protection for the engine from the moment of start-up.

This means that the synthetic oil is designed with improved lubricate properties and enhanced viscosity to provide superior protection from engine wear, reduced heat breakdown volatility for decreased oil consummation.
http://ezinearticles.com/?What-Is-The-Difference-Between-Synthetic-Oil-And-Conventional-Motor-Oil?&id=293637

Seth Brundle

http://www.carbibles.com/engineoil_bible.html

Wheelnut

Shannonsider wrote: »

I've had a look on the net and tried searching ...

You can't have looked too hard! The 'net is loaded with info about oils, here is one of the better ones:

http://www.carbibles.com/engineoil_bible.html

Esel

Shannonsider wrote: »

I am useless at googling. Can anyone help?

FYP