Engine Oil Route – How Engine Oil Travels(With Diagram)

The engine oil doesn’t just sit in the engine; it circulates through a carefully designed route, lubricating critical components, cooling hot parts, cleaning debris, and protecting against corrosion.

In this post, we’ll walk you through the entire engine oil route, using the labeled diagram to guide you step-by-step from the oil fill port to where the oil eventually returns to the sump.

So, let’s dive into it.

Engine Oil Route

1. Oil Fill Port

The journey begins here. This is where fresh engine oil is added during maintenance. From the oil fill port, the oil eventually drains down into the oil pan (sump) through the internal passages of the engine.

2. Oil Pan (Sump)

The oil pan, located at the bottom of the engine, acts as a reservoir. It stores the oil after it completes its cycle through the engine. When the engine starts, the oil pump draws oil from the sump.

3. Sump Strainer

Before the oil reaches the pump, it passes through a sump strainer, which acts like a pre-filter. It removes large particles or debris to prevent damage to the pump and other engine parts.

4. Oil Pump

The oil pump is the heart of the lubrication system. It draws oil from the sump and sends it under pressure through the main oil gallery. This pressure ensures that oil can reach even the furthest parts of the engine.

• Key Role: Provides the force necessary to circulate oil throughout the engine.
• Powered By: Usually driven by the crankshaft or camshaft.

5. Oil Filter

Immediately after the oil pump, oil is routed through the oil filter. This critical component removes fine particles, sludge, and contaminants from the oil, preventing damage and ensuring smooth engine performance.

Related Engine Oil Consumption Chart(For All Engine Types)

6. Main Oil Gallery

From the oil filter, the oil enters the main oil gallery, which is like a central oil highway. This gallery distributes oil to various parts of the engine including the main bearings, camshaft, and valve train.

7. Feed to the Main Bearings

Oil flows from the main gallery into the main bearings of the crankshaft. These bearings support the rotating crankshaft and are crucial for the engine’s operation.

8. Crankshaft Drillings

Internal crankshaft drillings direct oil from the main bearings to the connecting rod bearings. These are passageways drilled inside the crankshaft itself.

9. Crankshaft Connecting Rod Bearing

Here, oil reaches the big-end bearings of the connecting rods. This is where the connecting rods pivot on the crankshaft, and lubrication is vital to avoid wear and heat build-up.

10. Camshaft Bearing

Oil also flows to the camshaft bearings, which support the rotating camshaft. The camshaft controls the opening and closing of engine valves.

After lubricating the crankshaft and camshaft, the oil flows upward to the cylinder head area through dedicated oil passages.

Related Clearview Filtration Engine Oil Filter(Comprehensive Guide)

11. Cam and Tappet

Oil lubricates the cam lobes and tappets (or lifters), which translate the camshaft’s rotation into vertical movement. This movement is then passed to the push rods.

12. Push Rod

The push rods carry this vertical movement up to the valve rockers, and they are lubricated by oil passing through their hollow centers or through adjacent passages.

13. Valve Rocker

The valve rocker arms pivot on a shaft or stud, opening and closing the intake and exhaust valves. Oil lubricates the rockers and valves, and any excess oil drips back down to the sump via gravity.

14. Return to the Oil Pan

After completing its lubrication duties, oil naturally flows back down to the oil pan (sump) through gravity. For this purpose, there are small return holes and channels throughout the engine. Once in the sump, the oil is ready to be recirculated by the oil pump, and the cycle continues.

Related Engine Oil Weight Chart(Comprehensive Guide)

Step	Component	Function
1	Oil Fill Port	Entry point for fresh engine oil
2	Oil Pan (Sump)	Stores used oil for recirculation
3	Sump Strainer	Filters large particles before the pump
4	Oil Pump	Pressurizes oil for circulation
5	Oil Filter	Removes fine contaminants
6	Main Oil Gallery	Distributes oil to various engine components
7	Main Bearings	Lubricates crankshaft support
8	Crankshaft Drillings	Internal passages to connecting rods
9	Connecting Rod Bearings	Lubricates rod-to-crank connections
10	Camshaft Bearings	Lubricates camshaft rotation
11	Cam and Tappet	Transfers motion; receives lubrication
12	Push Rod	Transfers motion upward; oil travels through it
13	Valve Rocker	Controls valves; final lubrication point before return
14	Oil Returns to Sump	Gravity pulls used oil back to the reservoir

FAQ

What is the path of engine oil?

The engine oil follows a specific, cyclic route to lubricate and protect various engine parts:

1. Oil Fill Port – Fresh oil is added here.
2. Oil Pan (Sump) – Stores the oil at the bottom of the engine.
3. Sump Strainer – Filters out large debris before the oil reaches the pump.
4. Oil Pump – Pressurizes oil and begins its circulation.
5. Oil Filter – Cleans the oil of fine particles and contaminants.
6. Main Oil Gallery – Distributes oil to different parts like:
   • Crankshaft Bearings
   • Connecting Rod Bearings
   • Camshaft Bearings
   • Valve Mechanism (Tappets, Push Rods, Rockers)
7. Return Path – Gravity allows used oil to drain back into the sump.

This entire process repeats as long as the engine is running.

Why is my oil disappearing but no leak?

If your engine oil level drops but you see no visible leak, the most common reasons include:

• Oil Burn-off: Worn piston rings or valve seals can let oil enter the combustion chamber and burn off.
• High Oil Temperatures: Extreme heat can cause oil to evaporate or degrade faster.
• PCV Valve Issues: A faulty Positive Crankcase Ventilation valve can draw oil into the intake manifold.
• Turbocharger Oil Loss (in turbocharged engines): Oil can be consumed internally through the turbo seals.
• Sludge Build-Up: Old engines may have sludge deposits that trap oil internally.

Tip: A compression test or a look at the spark plugs (which may appear oily) can help diagnose the issue.

Related Engine Oil Compatibility Chart(A Detailed Guide)

Which direction does oil flow?

Engine oil flows from bottom to top and back down again:

• Starts at the oil pan → drawn upward by the oil pump.
• Flows through the oil filter → enters the main oil gallery.
• Distributes laterally to the crankshaft, camshaft, and valve train.
• Ends by draining downward via gravity into the oil pan.

So, the flow is upward under pressure, and then downward by gravity when returning.

How is oil distributed in an engine?

Oil is distributed through a network of internal oil passages and drillings:

• Oil Pump sends pressurized oil to the main oil gallery.
• From there, oil is channeled to crankshaft bearings, connecting rods, camshaft bearings, and hydraulic lifters.
• It also reaches valve rockers and springs through vertical passages and hollow push rods.
• After lubrication, oil returns to the sump through drainage holes.

This system ensures all moving parts are coated with a thin film of oil for protection.

Related Engine Oil Temperature Chart(Complete Guide)

What are the 7 functions of engine oil?

Engine oil performs multiple vital functions. The 7 primary functions are:

1. Lubrication – Reduces friction between moving parts.
2. Cooling – Absorbs and carries away heat from engine components.
3. Cleaning – Carries dirt, metal particles, and contaminants to the oil filter.
4. Corrosion Protection – Prevents rust and corrosion inside the engine.
5. Sealing – Fills tiny gaps between piston rings and cylinder walls for better compression.
6. Shock Absorption – Cushions engine parts under high pressure.
7. Noise Reduction – Quiets operation by dampening vibrations and metal contact.

What are the four 4 steps to checking the level of engine oil?

To check your engine oil properly, follow these 4 steps:

1. Park and Cool Down the Engine
   • Park on a level surface and wait at least 10–15 minutes after turning off the engine to let oil settle.
2. Locate and Remove the Dipstick
   • Open the hood and pull out the oil dipstick, usually marked with a bright handle.
3. Wipe and Reinsert
   • Clean the dipstick with a cloth, reinsert it fully, then pull it out again to check the oil level.
4. Read the Oil Level and Color
   • Oil should be between the “MIN” and “MAX” marks. It should be amber or light brown. If it’s very dark or gritty, a change is due.

Related Best Synthetic Engine Oil(Top 5 Best in 2025)