This topic appears regularly and always causes confusion!
Better oil will make your car run more efficiently (better power and economy) and will reduce wear so that optimum performance is retained for longer.
What do all the numbers mean?
This is a somewhat simplified explanation of a complex science!
Oil does several things, it lubricates, cools and carries crud from the engine to the filter. Most good oils lubricate about the same amount, all that's needed is a layer of oil to separate the moving parts.
Oil has two fundamental properties. Thickness (or viscosity) and lubricity. People often confuse the two, or assume that more viscosity means less wear. This is not the case! So long as the moving parts are kept apart by the oil, then it is doing it's job. Thick oil can cause problems though.
Oil's viscosity is represented by a number (or numbers). In the old days, the thickness was just one number (like 90, for nice thick "straight" gearbox oil). The higher the number, the thicker the oil.
Modern oils ("multigrade") have two numbers - the thickness when cold and the thickness when hot. The oil molecules do clever stuff as they heat up to do this. So a 10W-40 approximates a 10 oil (quite thin) when cold and a 40 oil (quite thick) when hot. Of course it's still thinner when hot than when cold, just not as much as a straight oil.
Thin oils are a good thing. On start up they will flow round the engine quicker and there will be less unprotected time. At speed, the thin oil will provide less resistance to pumping, and will therefore give a little bit more power or economy.
A manufacturer will design his engine for a certain type of oil. A rough old engine design may have bigger holes in it, and might require a nice thick oil so pressure is not lost on the way up the engine. A modern engine will have tight tolerances, and a thick oil will be a very bad thing, as it may take a very long time for the oil to get all the way around at startup.
A manufacturer will allow a range of oils to be used, but will normally recommend the thinnest oil in that range. In Honda's case, that thin oil is 0W-30. This oil will always maintain maximum lubrication (there will never be a point where it's so thin that the lubricating boundary layer will be broken) and it will be the quickest to get round your engine and will give the best power/economy.
An oil will break down and fill with crud over time. It may get thinner as time goes on too, and this is why it is vital to change it in accordance with the schedule. If it gets too thin, it may not provide the lubricating boundary layer.
Modern oils are made with a synthetic base - brands such as Castrol and Amsoil use a fully synthetic Type IV base, which will last the full schedule.
Oil temperature when running is maintained at roughly 90 degrees, since the water cooling system will be not far off that. In hot countries the oil will not run much hotter, since the engine will still be running at roughly 90 degrees.
If used in competition, engine temperatures may well be significantly different, and a thicker oil may be required.
1.8 and 1.4 Petrol cars
Capacity (1.4): 4.2 litres. Oil change 3.6 litres with oil filter, 3.4 litres with no oil filter change.
Capacity (1.8): 4.5 litres. Oil change 3.7 litres with oil filter, 3.6 litres with no oil filter change.
- Minimum allowed spec: 10W-40 mineral oil
- Castrol GTX Magnatec 10W-40 is allowed by Honda but not recommended by Castrol
- Good spec 5W-40 Semi synthetic or fully synthetic oil
- Best spec: 0W-30 Fully synthetic
- Castrol Edge 0W-30 (Castrol do not recommend a lower grade than this for the Civic, but Honda does)
- Mobil One 0W-40
- Honda allows 0W-20
2.2 Diesel cars
Capacity (2.2): 6.5 litres. Oil change 5.9 litres with oil filter, 5.5 litres with no oil filter change.
Allowed spec: 0W-30, 0w-40, 5w-30, 5W-40, 10w-40. Best spec: 0W-30 / 5w-30 Fully synthetic ACEA B5.
Honda strongly recommends that 0W-30 is the best oil to be used. Their testing shows a 2.5% improvement in fuel economy, it lowers emissions, lengthens the life of the catalytic converter, and reduces overall engine wear.
The i-CDTI non-DPF engine needs ACEA B3/B4 (HTHS>3.5) and ACEA B1/B5 (HTHS ≥ 2.9 and ≤ 3.5, preferred) specifications, and the DFP i-DTEC engine (new Accord) needs ACEA C3 (HTHS>3.5) and ACEA C2 (HTHS ≥ 2.9 and ≤ 3.5) specifications.
The cars are filled with Fuchs 0W-30 at the factory. UK internet store available online at http://www.opieoils.co.uk/p-985-fuchs-titan-supersyn-sae-0w-30-fully-synthetic-super-fuel-economy.aspx
The Honda branded oil is 5W-40 synthetic made by Idemitsu Oil of Japan.
All cars have two sensors, one to detect low oil level, and one to detect low oil pressure.
Low oil level
This will appear when the oil level is below the bottom line on the dispstick, and the words "LOW OIL LEVEL" may appear. No immediate damage should occur, but you should stop and top up the oil - and also work out why the level has dropped (oil leak maybe).
If the sensor fails, then the symbol appears with a ! after it.
The correct way to check the oil is not to rely on this sensor, but to regularly check the oil level with the dipstick.
Low oil pressure
This is accompanied by a red warning light and the words "LOW OIL PRESSURE" may appear. This means that the oil level is so low, that the oil pump is now not sucking oil and your engine is not being lubricated. So you only have a small number of seconds before irreversible damage is done. The correct action is to immediately stop the car and switch off the engine.
Checking the oil level
You must check the oil level regularly, since any damage to the engine that may have been prevented by the owner monitoring the oil level will not be covered by the warranty.
The engine should be fully warmed up, then parked on level ground, then left for 3 minutes.
Remove the dipstick and carefully clean it with a rag, making sure you leave no residue.
Fully insert the dipstick and then remove it again.
The level should be between the upper and lower marks (A and B in the diagrams), and it is approximately 1 litre between the lower and upper marks.
Do not overfill the engine! If the oil level is too high damage will be done. In a diesel the oil will cause the engine to rev up to the point of destruction (turning off the ignition switch will not stop it) and terminal damage will be done (see the example of MW57 FPK).