Before anything else, always check that the oil was topped up or changed properly because neglecting a few details could cost you much more than you saved by doing the operation yourself. First of all, make sure that you have screwed the cap back in correctly. No force is required. Just turn it as far as it will go. If the filler is not closed properly, the pressure generated inside the moving engine will find a release and the lubricant will start to seep out. The most immediate effect is the fouling of the engine compartment but travelling with insufficient pressure can damage the connecting rods and cause very expensive damage.
Never over the limit
On the contrary, immediate attention is required if the level is over the max line on the dipstick because the consequences can be just as serious. On petrol engines, the crankshaft gaskets could fail, while on turbo-diesel engines there is a risk of self-ignition which in the worst case would prevent you from stopping the engine even when you remove the key from the ignition switch. In both cases, simply slip under the car, loosen the drain plug and collect the oil in excess to restore the correct lubricant level.
Follow the handbook to avoid errors
Cars of relatively recent construction, specifically those made during the past 20 years, are designed to make it easier to check and top up the various liquids. Colour-coded caps and easily recognisable icons identify the various containers and their location is clearly indicated in the owner handbook, which is absolutely never a disgrace to consult in case of doubt. In addition to being prominently evident on the top of the engine, the oil filler cap can be recognised by the presence of a stylised oiler in relief. The dipstick is almost always on a side and has a yellow or red tip.
The challenge of the reservoirs
Slightly more puzzling for beginners may be identifying the coolant expansion vessel, the hydraulic brake circuit reservoir and the windscreen washer reservoir. They contain very different fluids with very different functions and must not be confused. Once again, the icons printed in relief or engraved on the caps and the owner handbook help to avoid mistakes. The semi-transparent vessels and reservoirs clearly show the maximum level to be reached. A mixture of glycol and water is poured into the expansion vessel of the radiator. The mixture raises the boiling temperature of the coolant and prevents freezing in winter. The braking circuit requires a stress-resistant fluid to ensure the necessary pressure, while detergent with antifreeze is used for the window washers.
Handle with care
The trickiest is the brake fluid which is corrosive and must be handled with care to prevent any drops from falling onto the bodywork and damaging the paint. Importantly, a quantity above the maximum level will not cause any problems. As a rule, braking systems do not require topping up, except in the event of leaks from the lines or as a result of wear on the pads. However, the level returns to normal when new pads are fitted.
If the liquid isn't right
If you made a mistake and used the wrong product, the most effective solution remains the emptying of the concerned circuit. The severity of your error depends on the type of liquid you used. In other words, filling the brake system reservoir with windscreen cleaner is more serious than pouring radiator antifreeze into the washer reservoir. However, you should take action promptly before the correct liquid and the one you poured in by mistake mix and go into circulation.