What is the difference between an oil filter and an oil pan?

Oil system problems in a fleet often come from a small overlooked part: the filter. Some buyers mix up the oil filter and the oil pan. They serve completely different roles. Confusing the two can lead to early engine wear, expensive downtime, and avoidable returns.

An oil filter actively removes debris from oil to protect engine components. An oil pan is a reservoir—it stores and cools the oil but doesn’t clean it.

A customer in the UK once told me his fleet kept suffering from early engine failure. The root cause? Low-grade filters that didn’t catch fine particles. Once he switched to our Runex oil filters, those issues disappeared. That taught me how much a filter can protect—or harm—an engine.

What is an oil pan?

Many first-time fleet buyers assume oil pans and filters are part of the same mechanism. They're not. The pan is the tank, the filter is the gatekeeper.

An oil pan is a metal reservoir located at the bottom of an engine. Its main function is to hold and cool the engine oil before it's pumped back into the system.

Think of it as a storage tank—not a filter

The oil pan¹’s job is simple: collect oil that drains from the engine, keep it cool, and feed it back into the circulation cycle. It doesn’t clean oil or screen out contaminants.

At Runex Auto, we work with engine builders and OEMs who look at oil system design holistically. One of their main concerns is oil temperature control². The oil pan helps here by exposing oil to airflow, especially in vehicles with undercarriage vents.

But no matter how efficient your oil pan is, it won’t save the engine if your oil filter³ fails. That’s where we focus our innovation.

Why oil pan and filter quality both matter

Without the right filter, the cleanest oil pan won't protect the engine. And without enough oil in the pan, even the best filter won’t work.

Can you change the oil filter without draining the oil pan?

This is a common question among new vehicle techs and some fleet buyers. The answer depends on how the oil system is designed.

In many vehicles, you can change the oil filter without draining the oil pan—especially if the filter sits above the oil level. But it's not always recommended.

Risk vs. convenience

Some filters are mounted vertically, on top of the engine. In these cases, minimal oil spills out during removal. In others, like horizontal side-mount filters, oil may drain quickly once removed.

I always advise my clients: if you're doing a full service, change both. Why? Because an old oil pan full of degraded oil will contaminate the new filter immediately.

We design Runex oil filters⁴ to seal tightly with anti-drainback valves⁵. These prevent oil from flowing backward when the engine stops. That means if someone does change just the filter, our design helps limit oil loss. But still—it’s best practice to drain and replace both together.

When it’s okay to replace only the filter

• Emergency maintenance (e.g., roadside filter leak)
• Filter clog or visible pressure drop
• Testing a new filter (e.g., in R&D)

When it’s not okay

• During regular oil service
• After engine overheating
• If the oil is dark, thick, or smells burnt

A full oil and filter change⁶ costs little compared to an engine rebuild.

What is the purpose of an oil filter?

This is where I always stop and explain things in plain terms: oil filters are not optional. They’re not accessories. They’re critical protectors of your engine’s life.

The oil filter removes microscopic contaminants from the oil—carbon, metal dust, sludge—before the oil flows back into the engine’s moving parts. Without a filter, oil recirculates harmful debris that causes wear.

More than just a screen—it’s a layered defense

Runex oil filter⁷s are built with multilayer media that traps particles as small as 10 microns. To put that in context: a human hair is about 70 microns wide. That’s how fine the protection has to be.

One of my UK clients used to source from a budget supplier. Their filters caught only coarse particles. Result? Sludge buildup in turbo systems and cylinder scoring in diesel engines. After switching to our filters, return rates dropped by 80% within six months.

Filter features that matter:

The oil filter doesn’t just trap dirt—it decides how long the engine stays clean inside. A bad filter doesn’t fail instantly. It damages the engine quietly, over time.

Should you drain the oil pan or oil filter first?

This may seem like a small detail—but the order of operations affects how well the service is done. It’s also something most new techs learn the hard way.

You should drain the oil pan first. This allows the oil in the system to flow downward, including oil held in the filter. If you remove the filter first, trapped oil can spill and make a mess.

Best practice order

1. Warm up the engine slightly – this thins the oil and makes it drain faster.
2. Turn off the engine and remove the drain plug – let the oil flow out completely.
3. Wait a few minutes – this lets oil in the filter move down into the pan.
4. Remove the oil filter – less oil left inside, less mess.
5. Replace the drain plug, then install new filter – clean threads, use proper torque.
6. Refill oil and check level – double-check for leaks after starting the engine.

This order isn’t just cleaner—it helps ensure the filter is not holding oil under pressure. Plus, it reduces oil waste.

Filter-first mistake

In one garage I worked with, a junior tech removed the filter first, spilling hot oil all over the alternator. Result? Smoke, panic, and a customer refund. That’s why we include oil change training⁸ in our Runex dealer onboarding.

Good filters help. But good habits matter⁹ too.

Conclusion

Oil pans and oil filters¹⁰ serve very different roles—but both are essential to a healthy engine. The oil pan stores and cools. The oil filter protects and cleans. Confusing them leads to service mistakes. At Runex Auto, we focus on building high-performance filters that trap the smallest particles and stand up to demanding use. When used correctly, our filters extend engine life, reduce returns, and support long-term fleet value. Whether you're managing a garage or a distribution network, knowing the difference—and choosing the right filter—makes all the difference.