If your car has racked up over 75,000 miles, you’ve probably heard that switching to a thicker oil—or high mileage oil—might be a smart move. But is it really necessary? Will it protect your aging engine or just make things worse?
Let’s explore this from a real-world driver’s perspective. Whether you’re dealing with oil leaks, engine noise, or just trying to extend your vehicle’s life, this comprehensive guide will help you understand if thicker oil is right for your high-mileage engine.
What Does “Thicker Oil” Mean?
Motor oil viscosity is expressed in grades like 5W-30, 10W-40, or 20W-50. The numbers represent how thick or thin the oil is at different temperatures. The higher the number, the thicker the oil.
| Oil Grade | Viscosity at Operating Temp | Common Use Case |
|---|---|---|
| 5W-30 | Thin | Newer engines, cold climates |
| 10W-40 | Medium | Older engines, moderate climates |
| 20W-50 | Thick | High-mileage or worn engines |
Why Consider Thicker Oil for High-Mileage Engines?
As your engine ages, it goes through natural wear:
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Seals shrink and harden
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Internal clearances expand
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Oil consumption may increase
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Burning oil becomes more likely
Thicker oil can help:
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Reduce leaks by being less prone to escaping worn seals
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Improve oil pressure
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Provide better cushioning between engine parts
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Minimize engine noise (ticking or knocking)
When Thicker Oil Makes Sense
You should consider using thicker oil if:
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Your engine burns or consumes oil between changes
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You notice leaks or seepage under your vehicle
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The engine sounds noisier, especially during startup
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You live in a warmer climate (thicker oil flows better in heat)
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You’re already above 100,000 miles and want more protection
When You Shouldn’t Use Thicker Oil
However, thicker oil isn’t always the answer. Avoid it if:
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You drive in very cold climates (thicker oil is harder to flow during startup)
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Your engine has tight tolerances and was designed for low-viscosity oil (like many modern turbo engines)
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Your manufacturer specifically warns against it
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Your car runs perfectly fine on the current recommended oil
Using oil that’s too thick can:
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Reduce fuel economy
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Make cold starts harder
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Lead to oil starvation in tight-clearance parts
Should I Use High-Mileage Oil Instead?
High-mileage oils are a better alternative to just going “thicker.” They’re specially formulated with:
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Seal conditioners to reduce leaks
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Detergents to clean old buildup
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Additives to protect worn metal surfaces
They’re available in common viscosities (e.g., 5W-30 high mileage), so you may not need to switch to a thicker grade at all.
Real-World Example
If your engine used to take 5W-30 and now burns oil or leaks at 120,000+ miles, moving to 10W-40 or a high-mileage 5W-30 can make a noticeable difference. You may see:
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Fewer top-ups between changes
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Reduced engine ticking
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Less oil dripping on the driveway
But always monitor performance after a switch and check your owner’s manual.
What Mechanics Say
Many mechanics recommend starting with a high-mileage version of your current oil grade. Only go thicker if:
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The problem persists
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You’ve confirmed your engine is showing signs of wear
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You’re not in freezing winter conditions
Summary Table: Should You Use Thicker Oil?
| Situation | Recommendation |
|---|---|
| Burning oil | Try thicker or high-mileage oil |
| Engine leaks | Thicker or high-mileage oil |
| Cold climate | Stick to manufacturer spec |
| Quiet, efficient engine | Keep using current grade |
| Engine noise/ticking | Consider thicker oil |
| Manufacturer doesn’t recommend it | Don’t use thicker oil |
FAQs
Q: Will using thicker oil damage my engine?
A: Not necessarily, but using oil that’s too thick for your engine’s design—especially in cold weather—can lead to oil flow issues and reduced protection during startup.
Q: Is high mileage oil always thicker?
A: No. High mileage oil may have the same viscosity as standard oil but includes additives for older engines. You can get high mileage 5W-30, 10W-40, etc.
Q: How do I know if my engine needs thicker oil?
A: Signs include increased oil consumption, leaks, engine noise, and high mileage (usually 100,000+ miles). If in doubt, consult a mechanic.
Q: Can thicker oil fix engine problems?
A: It might reduce symptoms like leaks and noise, but it’s not a repair. If there are major internal issues, thicker oil is only a temporary aid.
Q: Should I always follow the manufacturer’s oil recommendation?
A: Yes, especially for newer vehicles. But for older engines, a slight step up in viscosity or switching to high mileage oil is often acceptable.
Final Thoughts
Thicker oil can help extend the life of a high-mileage engine—but it’s not a silver bullet. In many cases, high mileage oil in your current grade is enough. Always weigh your climate, symptoms, and manufacturer recommendations before making the switch.
If in doubt, talk to a trusted mechanic and keep an eye on how your engine performs after any change.
