How to check the oil

Park the car on a level spot, turn the engine off and set the hand brake. Locate the engine oil dipstick, pull it out, wipe it off with clean cloth and insert it back. Pull it out again and have a close look. If you've never checked the oil level before, follow this link for detailed guide How to check engine oil.
If you find the oil is completely black (although for the Diesel engine black oil is normal) and (or) the oil level is very low (left picture) - suspect excessive oil consumption and (or) lack of maintenance. In either case the engine will more likely to have problems in the future. Another sign of poor maintenance would be dark stains (carbon deposits) covering the oil dipstick along its length.
Well maintained engine will more likely to have cleaner oil and the proper oil level (right picture), although this doesn't necessarily mean that the engine is in good shape; the oil just could have been changed recently.

How to check the car engine when buying a used car

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Please note, this article is designed to give you an initial idea about what to look for when buying a used car and might possibly help you to avoid some used cars with potential problems, but it can not substitute for a detailed mechanical inspection performed by a professional. As a final step before purchase, take the car to a mechanic of your choice for thorough mechanical inspection. Use caution when doing any tests on a car, If you don’t feel comfortable doing any of these tests, have the car inspected by a mechanic.

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Imagine, you are shopping for a used car. You enter the dealership and see that nice-looking car. You love it from a first sight. Meanwhile, the salesperson hanging around and telling you that regular story that, the car was lady driven and the engine works like a clock, and this is only "Today special" - "We need to clean inventory!", and you are so lucky because they are selling it very cheap - "We even lose money on this deal!" and that you have to give a deposit right now or else you will regret about it for the rest of your life! - Sounds familiar so far?
You decided - "deal!" - shaking hands, you're happy, salesperson is happy. Finally, you got your new wheels.
Few weeks later you notice blue smoke when you're starting the car in the morning. Few months later you discover that there is no oil left in the engine and finally got your car towed to the garage. "The engine is gone - has to be rebuilt" they diagnose.
In fact it's quite common scenario.
This article will give you an idea an may help you to avoid such a troubles buying a used car.
However, it's always good idea to have the vehicle inspected by a specialist prior purchase. This is what I'd recommend to any used car buyer.

The Clean Engine Vehicle Project

		A joint project between Empa (Internal Combustion Engines Laboratory) and ETH (Aerothermochemistry and Combustion Systems Laboratory and Measurement and Control Laboratory).

Natural gas and biogas are counted among the cleanest fuels. Modern natural gas vehicles emit less pollutants as gasoline or diesel driven vehicles and also the effect based assessment of the exhaust emissions is better: the ozone forming potential of the hydrocarbon fraction is much lower, the content on carcinogenic components as benzene, 1.3-butadiene, formaldehyde or acetaldehyde is nearly not measurable and the particulate emissions are near zero. Natural gas vehicles have additionally a big potential for a CO2 reduction. Alone, based on the lower content of carbon in the fuel, the CO2 reduction of a natural gas driven vehicle is about 20%, compared with a gasoline vehicle. Based on the high knock resistance of natural gas, advanced dedicated natural gas vehicles can be optimized regarding higher energy efficiency. Such vehicles have the potential for a CO2 reduction of 30%. With the project “Clean Engine Vehicle”, Empa and ETH demonstrated the potential of such an optimized natural gas vehicle regarding pollutants and CO2 reduction with todays engine technology. Within the project, an actual gasoline driven engine was converted to dedicated natural gas operation, the compression ratio has been optimized, a catalytic converter was developed and a downsizing concept (supercharging with boost control and gear box modifications) was realized. Aim of the project was a CO2-reduction of 30% in the official European driving cycle compared with a similar powered gasoline vehicle and the compliance with the most stringent European and Californian exhaust gas limits for Euro-4 and Super-Ultra-Low-Emission-Vehicles (SULEV).

Fig. 1		The pollutants could be reduced below the targeted limits (Fig. 1). The NOx concentrations were after a driving distance of about 300 m after cold start even in transient driving always lower at tailpipe then in the intake air of the engine (Fig. 2).

Fig. 2		Compared with a gasoline engine with similar performance, the CO2 emissions could be reduced at 31% (Fig 3). The most important CO2 reduction of 22% could be realised by the conversion to natural gas operation and is based on the lower carbon content of natural gas compared with gasoline.

Fig. 3

Simultaneously, the maximum engine power was reduced at about 15% by the gas induced reduction of engine filling. The increase of compression ratio resulted in a further CO2 reduction of 2.7% and the maximum engine power could be increased by 6.5%. The supercharging and gearbox modifications reduced the CO2 emissions again by 3.4% and increased the maximum engine power by 33%. With all this measures, the maximum engine power was increased by 20% compared with the basic 1.0 l gasoline engine.

Internal combustion engine

From Wikipedia, the free encyclopedia

An automobile engine partly opened and colored to show components

The internal combustion engine is an engine in which thecombustion of a fuel occurs with an oxidizer (usually air) in acombustion chamber. In an internal combustion engine the expansion of the high temperature and pressure gases, which are produced by the combustion, directly applies force to a movable component of the engine, such as the pistons or turbine blades and by moving it over a distance, generate useful mechanicalenergy.^[1][2][3][4]

The term internal combustion engine usually refers to an engine in which combustion is intermittent, such as the more familiar four-stroke and two-stroke piston engines, along with variants, such as the Wankel rotary engine. A second class of internal combustion engines use continuous combustion:gas turbines, jet engines and most rocket engines, each of which are internal combustion engines on the same principle as previously described.^[1][2][3][4]

The internal combustion engine (or ICE) is quite different from external combustion engines, such assteam or Stirling engines, in which the energy is delivered to a working fluid not consisting of, mixed with or contaminated by combustion products. Working fluids can be air, hot water, pressurised water or even liquid sodium, heated in some kind of boiler by fossil fuel, wood-burning, nuclear, solar etc.

A large number of different designs for ICEs have been developed and built, with a variety of different strengths and weaknesses. Powered by an energy-dense fuel (which is very frequently petrol, a liquid derived from fossil fuels) the ICE delivers an excellent power-to-weight ratio with few safety or other disadvantages. While there have been and still are many stationary applications, the real strength of internal combustion engines is in mobile applications and they dominate as a power supply for cars, aircraft, and boats, from the smallest to the biggest. Only for hand-held power tools do they share part of the market with battery powered devices.