I wrote this article for an automotive technology class I took in 2005. It is basically a visual guide showing how to inspect your vehicle "under-the-hood" to make sure things are running smoothly.



This guide provides some guidelines as to how to conduct a regular, under the hood inspection of your passenger car. The document follows a step-by-step approach with pictures showing what to look for regarding each of the items to be inspected. A Mazda Millenia is used in this guide as an example. Obviously, your car may look different so you should also consult your own car owner’s manual before proceeding. This type of inspection is relatively simple and should be performed regularly. It is suggested that you perform this inspection every time you fill-up the gas-tank.

Figure 1 below shows how the car looks under-the-hood and outlines the key points of interest. In the following sections we will be discussing each of these inspection points in further detail.


Figure 1 – Under the hood overview

engine oil

Ensuring that your engine is well lubricated is key to maintaining your engine’s health and preventing overheating, arguably your car engine’s worst enemy.
It is usually advisable to let the engine cool for about five minutes before measuring the oil level. You should also make sure the car is in a leveled surface. Check the oil level using the “oil stick” provided (see Figure 2 below). If the oil level is low, add more oil to the engine by unscrewing the oil cap (See Figure 3).

Figure 2 – Oil stick

Check the oil color and viscosity. The oil should not be excessively black or too thick. If it is, you may want to change the oil.

Figure 3 – Oil cap


radiator fluid

Identify the radiator fluid reservoir is on your vehicle and check the coolant level (See Figure 4). If it is too low, you need to add more coolant. In this example, the fluid was above the “Low” line so no action was needed.

Figure 4 – Coolant Reservoir

Remove the coolant cap and check the condition of the rubber sealing. If you find cracked or swollen gaskets then the cap needs to be replaced. The cap usually indicates the rated pressure, in this example 1.1 bar (See Figure 5). If you have the tools, you can pressure test the cap to detect leaks in the cooling system.

Figure 5 – Radiator cap

Inspect the hoses around the reservoirs to detect any cracked or swollen hoses or signs of coolant leaks. In this case, we detected a small leak at the entrance to the reservoir (See Figure 6). In this case, it is recommended that the hose and/or the tank be replaced.


Figure 5 – Coolant Leak

air filter

The air filter protects the engine against abrasive particles in the incoming air. Over time, the filter accumulates dust and if too dirty, it may become ineffective.  Figure 6 shows the air filter box and a detail of the latches that release the top cover.


Figure 6 – Air Filter Box


Remove the cover (See figure 7) to access the air filter.

Figure 7 – Air Filter Box

Remove any dirt or leaves that accumulated in the box. The air filter was a little dirty in this example (see Figure 7) but not enough to warrant replacement. Remove as much dust as you can from it and insert it back in the box. If the filter is too dirty, replace it with a new one.

Figure 8 – Air Filter Box



Batteries contain sulfuric acid which is a very corrosive chemical. Inspect the battery terminals and the area around the battery for signs of corrosion. This may indicate a bad (leaking) battery. If needed, clean the area with baking soda. Make sure the battery is firmly attached to the frame (See Figure 9). A loose battery may vibrate excessively when the car is running and eventually loosen the battery terminals.
Check the water level in each cell to make sure is adequate. If you have a “maintenance-free” battery, you don’t need to check water level.

Figure 9 – Battery

Make sure the cables attaching to the battery terminals are tightly connected. Check for corrosion build-up and clean if necessary (See Figure 10).

Figure 10 – Battery Terminals

brake fluid

Check the brake fluid reservoir to make sure it is at the recommended level in the owner’s manual. In this case, the owner’s manual recommended that the fluid be at the “MAX” level so we had to add more fluid to the reservoir. Always check the manual for the correct type of fluid for your vehicle. Brake fluid types vary depending on whether your car has ABS or not etc.
Inspect the fluid visually and make sure it is not muddy and that there are no visible particles floating on it.

Figure 11 – Brake Fluid Inspection

fuse box

The fuse box is typically well marked and can be removed by removing a simple latch by hand (See Figure 12). Inspect the fuses visually first. If a larger fuse is blown-up, you can usually detect it visually. The smaller fuses can be verified using a multi-meter in Resistance mode (Ohms). The fuse should read close to zero Ohm for a good fuse and a very high resistance (or infinity mark) for a blown-up resistor. Some multi-meters have an audible “continuity/diode test mode” that will beep if the fuse is good and will not beep otherwise.


Figure 12 – Fuse Box

transmission fluid

Identify the transmission fluid reservoir (refer to the owner’s manual if necessary). Make sure there fluid level is above “MIN” or as recommended in the manual. Add more fluid if needed.

Read the manual to determine the correct type of transmission fluid for you car as this varies from vehicle to vehicle. Most manufacturers recommend that you check the transmission fluid with the engine running and the car on park, but there are exceptions. Once again, check your owner’s manual to find-out the correct procedure.


Figure 13 – Transmission Fluid Inspection

windshield washer fluid

Identify the windshield washer fluid reservoir (refer to the owner’s manual if necessary) and make sure there fluid level is above “MIN” or as recommended in the manual. Add more fluid if needed. Remember that, even though the windshield washer fluid is not need to make the vehicle run, it can be hazardous to operate the car without fluid, especially in dusty or muddy roads where the windshield driving visibility can be compromised.


Figure 14 – Windshield Washer Fluid Inspection

belts and hoses

Inspect your belts visually to make sure there are no cracks or fraying. Belts should be replaced when these problems surface. Inspect all the visible hoses and make sure they are not swollen or cracked. Check for fluid leaks along the body of the hose and near junctions. Squeeze the hoses to get a feel for their condition.

Comments, questions, suggestions? You can reach me at: contact (at sign) paulorenato (dot) com