Winter Storage: Oil Change Before or After?

As the chill of winter approaches and thoughts turn to tucking away your vehicle for an extended period, perhaps while you're away at college for nearly ten months, a critical question often arises: should you change your car's engine oil before or after storage? It's a common dilemma, and while opinions vary, the consensus among automotive experts leans heavily towards one particular approach, especially when safeguarding your engine's long-term health is the priority.

Let's consider your specific situation: your M1 full synthetic oil was last changed last August and has accumulated approximately 5,500 miles. Your M1 extended performance oil filter, however, dates back to October 2017 and has seen about 12,000 miles of service. With such a significant storage period ahead, understanding the nuances of oil degradation and its impact on your engine is vital.

The Silent Threat: Why Used Oil is Your Engine's Enemy During Storage

Engine oil, while a marvel of lubrication and protection, doesn't remain in pristine condition indefinitely. As it circulates through your engine, it performs several critical functions beyond just reducing friction. It cleans, cools, and protects internal components. However, this process inevitably leads to contamination. During combustion, by-products such as soot, unburnt fuel, and moisture inevitably find their way into the oil. Crucially, these contaminants, combined with the extreme heat cycles, lead to the formation of acids.

These acids are the primary reason why leaving old oil in your engine during long-term storage is a risky proposition. The corrosive action of these acids is relentless and is not dependent on the engine running. Even when your car is stationary in a garage, these acidic compounds will continue to attack the various metallic components within your engine. Softer metals, such as those found in crank bearings (often made of materials like lead, copper, and tin alloys), and even aluminium engine components, are particularly vulnerable to this silent, insidious corrosion.

Fresh engine oil, on the other hand, is rich in additives specifically designed to neutralise these acids, suspend contaminants, and prevent corrosion. Over time and mileage, these additives get depleted, leaving the oil less capable of performing its protective duties. When your car is parked for months on end, the depleted, acidic oil simply sits, allowing these corrosive elements ample time to etch away at vital engine parts. The cleaner the inside of the engine, with minimal contaminants and fresh, potent additives, the better protected it will be during its extended slumber.

The Role of the Oil Filter in Long-Term Storage

Just as important as the oil itself is the oil filter. Its job is to capture and hold contaminants, preventing them from recirculating through the engine. Your M1 extended performance filter, while designed for longer intervals, has already accumulated 12,000 miles and is over six years old. This is a significant amount of service and time for any filter.

A filter that has reached its capacity or is nearing it will be saturated with the very contaminants and acidic sludge we've been discussing. Leaving such a filter in place during storage means that your engine is sitting with a reservoir of harmful particles and acidic residue. While the engine isn't running, the trapped contaminants can still contribute to the overall acidic environment. Furthermore, a clogged filter can sometimes lead to the oil bypass valve opening prematurely when the engine is eventually restarted, sending unfiltered oil directly to the engine's critical components. Therefore, for optimal protection, both the oil and the filter should be replaced.

The Verdict: Change Before Storage

Given the information above, the unequivocal recommendation for your situation is to change both the engine oil and the oil filter before you store your car for the winter. This ensures that your engine is filled with fresh, clean oil, packed with its full complement of protective additives, and free from corrosive contaminants. It's an investment in your engine's longevity and peace of mind.

Why Not After Storage?

Waiting until after storage means your engine would have spent ten months bathed in used, acidic oil, allowing corrosion to take hold. While you'd eventually replace the oil, the damage, however microscopic, would have already occurred. Prevention is always better than cure when it comes to engine health.

Other Fluids to Consider for Long-Term Storage

While engine oil is paramount, many articles and experts will insist you change all fluids if you are not going to use the car for several months. And it makes perfect sense. While other fluids might be less susceptible to environmental and condensation effects than engine oil, they still play a crucial role in the vehicle's overall health.

• Coolant/Antifreeze: This fluid not only prevents freezing and boiling but also contains corrosion inhibitors that deplete over time. An annual replacement of coolant is generally a good idea anyway, but it's particularly important for long-term storage to ensure maximum corrosion protection for your cooling system components.
• Brake Fluid: Brake fluid is hygroscopic, meaning it absorbs moisture from the air. Over time, this absorbed water can lead to internal corrosion within the brake system and reduce braking efficiency. While not as critical for immediate engine protection during storage, ensuring its good condition contributes to overall vehicle health.
• Fuel: For very long storage periods, it's advisable to either fill the fuel tank completely to minimise condensation or, conversely, run it nearly empty and add a fuel stabiliser. A full tank reduces air space where condensation can form, while a stabiliser prevents fuel degradation and gumming, which can clog fuel lines and injectors.

The Peril of Short Engine Runs During Storage

A common misconception among car owners storing their vehicles is that periodically starting the engine and letting it run for a few minutes will keep everything lubricated and healthy. This couldn't be further from the truth, and in fact, it can be significantly more detrimental than leaving the car untouched.

When you start an engine for a short period, it rarely gets hot enough to evaporate the moisture and condensation that builds up within the engine and exhaust system. This moisture, combined with combustion by-products, rapidly forms more acidic compounds that then mix with the oil. Furthermore, a cold engine run means the oil doesn't reach its optimal operating temperature, where it can effectively circulate, clean, and activate its protective additives. Unless you can run the engine long enough – typically 20-30 minutes or more, until it reaches full operating temperature and stays there for a while – to burn off all condensation from the oil and exhaust, it's best not to start it at all. A short run simply adds more moisture and acid to the oil without allowing it to dissipate, exacerbating the very problem you're trying to avoid.

Comparative Considerations: Before vs. After Storage

To summarise the core dilemma, here's a quick comparison:

Frequently Asked Questions About Car Storage and Oil

Is synthetic oil better for storage than conventional oil?

While synthetic oils are generally more stable and resistant to thermal breakdown and oxidation than conventional oils, they still accumulate contaminants and acids from engine operation. Therefore, even with full synthetic oil, the principle of changing it before long-term storage remains the same due to the acidic by-products it collects.

How long can oil sit in a stored car before it becomes a problem?

The primary concern isn't the oil 'going bad' just by sitting, but rather the contaminants and acids already present in used oil. Even if the car sits for only a few months, these acids can cause damage. For storage periods exceeding a couple of months, an oil change is highly recommended.

What should I do with the oil filter?

Always replace the oil filter along with the oil. A dirty filter is saturated with contaminants and acidic sludge, which can continue to affect the engine environment even when stationary. Your filter, with 12,000 miles and over six years of age, is well past its prime for any scenario, let alone long-term storage.

Should I fill the fuel tank before storage?

Yes, generally it's advisable to fill the fuel tank completely and add a fuel stabiliser. A full tank minimises the air space, which in turn reduces the potential for condensation to form inside the tank. The fuel stabiliser prevents the petrol from degrading and forming gums or varnishes that can clog your fuel system over time.

What if I absolutely must start the car during storage?

If you find yourself in a situation where you absolutely must start the car, ensure you run it for at least 20-30 minutes, or even longer, until the engine reaches its full operating temperature and stays there for a sustained period. This allows all moisture to evaporate from the oil and exhaust system. Anything less than this is detrimental.

Conclusion

For your vehicle, with its current oil having 5,500 miles and its filter 12,000 miles and over six years old, the recommendation is clear: change both the oil and the oil filter before storing your car for the next ten months. This proactive measure will protect your engine from the corrosive effects of acidic, contaminated oil, ensuring that when you return next summer, your car is ready to go with a healthy, well-preserved engine. It's a small investment that offers significant returns in the form of engine longevity and reliability.

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