A common question is 'Which oil should I use?'
There's three categories of engine oil:
- Fully synthetic
- Semi synthetic
As a general rule of thumb, fully synthetic is the best - and the most expensive.
Semi synthetic is a blend of synthetic and mineral oil, and mineral oil is lifted out a hole in the ground in a bucket.
Oil is also given a rating of 0-30W and 5-40W. There's others, of course. This rating just refers to the viscosity - the thickness of the oil under certain conditions. 0-30W is a thinner oil than 5-40W.
At one time people used to use a thicker oil in their car engine during the winter months and a thinner oil during the summer months.
Fully synthetic 0-30W oil is often specified for engines that have 'zero tolerance'. Here, zero tolerance simply means no space between the metal of the piston and the cylinder wall. The oil must be thin enough to be able to coat the mating metal surfaces and yet be robust enough to withstand the pressures of what is basically pressurised metal to metal contact.
Using semi synthetic oil in a zero-tolerance engine will cause very rapid wear indeed. Topping up a zero-tolerance engine with mineral oil can have catastrophic results. Not only does it not afford protection but it - the mineral oil - will form a 'globule' - a ball - inside the oil sump/pan that will block the oil pump pick-up with absolute catastrophic results - very quickly.
In Europe the Saab 9-5 model had, amongst others, a V8 3000c diesel engine fitted. It was a zero-tolerance engine. Many of these cars ended up with wrecked engines simply because owners had topped up with the wrong oil. And, on a zero-tolerance engine the oil level itself is critical so much so that Saab modified the oil dipstick so that owners overfilled with oil by 1 litre. A zero-tolerance engine doesn't tolerate a 'slightly lower' oil level.
Most drivers wouldn't know if their car was a zero-tolerance engine. If you use fully synthetic 0-30W (or follow the manufacturer's recommendation) you won't go far wrong. You can use fully synthetic 0-30W in your 1956 Cadillac if you wish. It won't harm it.
Other grades of fully synthetic are fully suitable for all non-zero tolerance engines.
The difference between fully synthetic (apart from the price) and semi synthetic and mineral is that of durability. Fully synthetic 'breaks down' slower .. in other words, it lasts longer as a 'lubricant' ... does its job better.
Short journeys destroy engine oil - particularly mineral oil. Toxins and carbons accumulate in the oil and cause it to break down into 'sludge'. Semi synthetic oil is more resistant to breaking down, and fully synthetic is even better.
If you've got a decent car with a decent engine - use fully synthetic 0-30W. If it isn't a 'zero-tolerance' engine use any fully synthetic oil or semi synthetic oil.
If you have an old 1998 4 litre Jeep that burns oil like I have, a cheap mineral oil will do. But do change the oil and filter regularly. Regular oil/filter changes promotes the life of your engine - irrespective of what car you drive - and it really does prevent mechanical problems such as noisy camshafts/engine knocks.