The Underside Of Your Car

What’s on the underside of your car? The only time you might find me under my truck is if there is a problem I can’t ignore anymore. The underside of your car is where you will find some major components, and major grease, dirt and filth! But if you have ever thought, “What the heck is a freeze plug? It sounds like it could be important. It’s on my car? Where?” then it’s time to get down and look under the engine with me.

While we’re wallowing around in the muck under the engine we’ll check out what else is on the underside of your car!

This article relates to the article What’s Under Your Hood. An article that takes a look under the hood of your car and identifies important components.

We will be looking under a 1989 Chevrolet Silverado Dually. Why did I choose the 1989 Silverado Dually? Simple reason, because I don’t have to jack it up or put it up on a lift. I can slip right under it! Only after I’ve set the emergency brake, choked all the wheels, of course.

These are the components that are found under all cars, not only the Silverado.

  • Oil pan.
  • Transmission oil pan.
  • Freeze plugs.
  • Headers.
  • Catalytic Converter.
  • Exhaust pipes.
  • Frame.
  • Suspension.
  • Fuel tank.
  • Drive shaft.
  • Pumpkin.
  • Spare tire (Some models have the spare tire elsewhere like the trunk).

Oil Pan ~

Oil pan and can.

Just behind the engine you will find the oil pan. In the picture above you can also see the oil filter.

  • At the front of the oil pan is the drain plug. This is where you drain the oil for an oil change.
  • The oil filter is screwed on, hand tight only. When you change the oil, unscrew the can and put a new one in its place.
  • This links to our article on Changing the Oil in Your Car.

Transmission Fluid Pan ~

Transmission fluid pan.

The oil for the transmission is in this pan. You can read up on changing the transmission fluid here. The pan is protected by the frame of the truck. If the transmission pan is damaged it can cause the transmission fluid to leak out.

Freeze Plugs ~

Freeze plug viewed through the wheel well.
Freeze plug close up.

Peek through the front tire wheel well. Sometimes you can espy some of the freeze plugs as pictured above.

  • Freeze plugs are located on the under sides of your engine.
  • There are three, or more, along each side of the engine.
  • They are made of steel, or brass, and press fitted into prefab holes.
  • If the engine is exposed to freezing temperatures the freeze plugs expand and may pop-out in an effort to relieve the engine of the fluid that is expanding as it freezes.
  • Freeze plugs can leak, especially if the engine has been exposed to frosty weather.
  • Intermittent radiator fluid loss may be due to freeze plug partially displaced or a leak in one, or more.
  • You can replace freeze plugs if they are leaking.


  • Headers are attached to the side of the engine above the spark plugs.
  • When the spark plug detonates inside its cylinder the exhaust created from the internal combustion must leave the engine in preparation for the next detonation that makes your engine run. The headers direct the exhaust from the internal combustion in the cylinder out of the engine. Each cylinder has its own header pipe.
  • Each pipe whether it be four on each side for a V8, three on each side for a V6, or two on each side for a four cylinder, they come together into one head, hence the name headers.
  • Headers can effect the performance of the engine especially if they are too small to accommodate all of the exhaust the cylinder is expelling.
  • The main problem you may come across with headers is they crack over time and use. Headers may crack as they age, or are exposed to over heating, or damage from other engine components breaking and hitting them.
  • Headers are not usually a system component that need any type of regular maintenance.
  • Some people exchange the stock headers to performance type for more power.

The Catalytic Converter

The catalytic converter.

To find the catalytic converter(s) under your car, follow the headers towards the rear of the vehicle. They are not far from the headers. Approximately under the front seats of the car.

As defined by the online Dictionary, a catalyst is: A substance that increases the rate of a chemical reaction without itself going under any permanent chemical change.

  • Thus, the catalytic converter contains a substance, platinum and palladium, both catalysts, to filter the exhaust from your engine.
  • Depending on your engine size there may be one, or two, catalytic converters. One for each side, or one for both sides.
  • Without a catalytic converter your vehicle will not pass a smog test.
  • It can interfere with performance by restricting the exhaust process. They can be replaced, or sometimes the filters can be cleaned.
  • Poor acceleration, excessive heat under your seat and black smoke from your exhaust are all signs of the catalytic converter failing.
  • The catalytic converter is prized by thieves because of the precious metals it is made of.

Exhaust Pipes

The exhaust pipes are connected to the catalytic converter. As the exhaust is filtered through the catalytic converter it is directed to the rear of your vehicle via exhaust pipes. They can usually be seen coming out from under the car to expel the filtered exhaust out to the open air.

  • Again, if you are experiencing performance issues the exhaust pipes may be the culprit. Usually when an exhaust system is modified the entire system is changed. It doesn’t make much sense to install high performance headers if your not going to install exhaust pipes that can’t accommodate the high performance headers.
  • Exhaust pipes can last the lifetime of the vehicle without maintenance.
  • The exhaust coming out of the pipes can help diagnose engine problems. A blown head gasket might produce a moist exhaust. Placing your hand outside of the exhaust pipes your hand will become wet with all the moisture from the blown engine. Black smoke can indicate a clogged catalytic converter or a carburetor in need of tuning or a problem in the ignition system.

Vehicle Frame

Vehicle Frame

The vehicle frame is exactly that, the frame. It is also, more commonly, known as the chassis. It’s the skeleton when everything else is removed.

  • The front of the frame has reinforcement bars in order to carry an engine.
  • Frames are made in various styles depending on the vehicle type, and engine, that will be placed on it.
  • When jacking up a vehicle, or lifting on a vehicle lift, the frame is where the vehicle should be lifted by, not the body of the car that fits over the frame. The body is made of a material that will not withstand lifting.


Rear suspension shock absorber.

The suspension includes the springs, or leaf springs, shock absorbers or struts. You will not have both shock absorbers and struts.

  • You will find a spring at every wheel. The type will vary.
  • Leaf springs are mounted in the rear. You will not find leaf springs on the front wheels normally.
  • Shock absorbers are mounted in the rear. Older model cars may have shock absorbers in the front.
  • Struts are on the front wheels. They are part of the suspension and steering.
  • Struts are a combination of a shock absorber surrounded by a spring. It must be considered when adjusting the steering.
  • The outside spring of a strut contracts with a bump in the road while the inside shock absorber reduces the impact of the bump.
  • On this Chevrolet 3500 it incorporates both leaf springs and shock absorbers in the rear.

Fuel Tank

Fuel tank.

The fuel tank is located near the inlet spout for filling your car with fuel.

Once upon a time, long, long, ago, there was a vehicle named Pinto that came out. Unfortunately, when the engineers designed the Pinto they had left their thinking caps at home. This made the design of the Pinto highly dangerous. The engineers decided it would be a good idea to place the fuel tank in front of the drive shaft Thus, if the Pinto was hit from behind, the drive shaft would be propelled like a spear, or harpoon, into the gas tank which would burst into flames. But without their thinking caps on, the engineers did not realize this. When the Pinto came out, people liked it. A lot of people bought it. When these people were involved in rear end accidents they found themselves in an explosion of flames. The Pinto was recalled for this error. The problem was fixed with a handful of grease smeared on the gas tank itself, or a steel plate attached in front of the drive shaft. The idea was the grease, or steel plate, would deflect the drive shaft from puncturing the gas tank if hit from the rear in an accident. My Pinto had the blob of grease on the gas tank. The moral of this story, don’t design a vehicle where anything resembling a spear or harpoon, like a drive shaft does, can puncture the gas tank because it is flammable!

Drive Shaft

The drive shaft is how the power from the transmission gets to the wheels. It comes out of the transmission and heads back to the differential that disperses the power to each rear wheel.

The Pumpkin AKA: Rear Differential

Rear differential with filler plug noted.
  • The drive shaft attaches to the rear differential, or pumpkin as many people call it.
  • The differential then transmits the power from the drive shaft to the rear wheels.
  • The arrow is pointing to the filler plug for the differential. When work is done, such as brakes on a dually, this plug needs to be removed so you can add fluid and then screwed back in.

Spare Tire

Spare tire attached to the front of the vehicle.
Spare tire attached to the rear of the vehicle.

Your car floats on air that is held in a big rubber balloon called a tire. If that balloon pops, which they do, you need to be able to put a spare tire on.

Every car that rolls out of a dealerships driveway has a spare tire on it. . . somewhere. Every car will also have the means to change the tire, again, somewhere. The location of the spare tire, jack and crow bar are recorded in the owners manual. Or, you can look around and under your vehicle to find it yourself. The various locations may be:

  • Attached to the front of the car like pictured above.
  • Inside the hood, if the engine is located in the trunk.
  • Attached to the rear like pictured above.
  • Inside the trunk under a false trunk bottom.
  • In the back side wall inside.
  • At the back of the vehicle underneath it. When the spare is located under the vehicle such as with the Chevrolet Silverado and Ford Explorers, there will be a rod that you use to lower the tire down.

That covers the major components under your car! The engine may have electronic components attached to the lower section of the engine, but that will take an article of its own. Thanks for stopping in!

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