If your car’s engine is showing wear and you’re unsure if 5w30 or 10w30 is best for your high mileage engine, then you’ve come to the right place. In this article, we’ll discuss what happens to an engine during its lifetime, how high mileage oil helps, and hopefully, put an end to the 5w30 vs 10w30 debate.
What Is Considered High Milage?
It depends on the conditions the car was subjected to. Highway miles are considered as less taxing on the engine than city miles. There are very few stops, thus the engine temperature and load are steady for long periods of time.
On the other hand, city driving is the opposite. Stop and go traffic means uneven engine load and engine temperature, leading to increased engine wear when compared to highway miles.
But to give you a number, consider anything over 100,000 miles a high mileage car.
What Happens to an Engine Over Time?
Let’s talk about what happens to an engine when it ages. Car engines have a lot of moving parts, which wear due to friction over time. Since worn parts lose their mass, tolerances in the engine increase. For example, a bigger gap between the valve stems and rocker arms produces a loud tapping sound – a symptom that you need a valve adjustment to decrease the worn-out tolerance.
Long gaps between oil changes will cause sludge buildup over time. Even rubber seals and gaskets will dry up due to age and constant temperature changes, shrink and start causing leaks. All of these parts will wear out at different rates due to the properties of the material they are made of.
High mileage oil is specifically designed for engines that are starting to show wear. A high mile oil is packed with special additives:
- Viscosity modifiers that keep the oil thicker for a longer amount of time, thus compensating for the looser internal tolerances longer
- Seal conditioners that swell the seals and gaskets up to stop oil leaks
- Detergents that fight sludge buildup
- Friction modifiers
- Anti-corrosion agents
Now, nothing that comes in a bottle will fix something as serious as blowby or cylinder slap. However, if you have a well-maintained vehicle that’s showing a bit of wear, a high mileage engine oil could mask the symptoms. Just don’t think that high mileage engine oil is a way to fix engine wear.
The Final Verdict on 5w30 vs 10w30
Both high mileage 5w30 and 10w30 engine oils have the same additives, the only difference is the viscosity at cold startups. Since both oils have the same operating temperature viscosity (30) and additives, they will perform exactly the same.
However, 5w30 flows much better than 10w30 during cold starts. And considering that studies show that most engine wear occurs when the engine is cold (hasn’t reached the operating temperature of 195 – 220 oF), 5w30 is the better option.
Now, if your car’s engine is badly worn (worn main bearings etc.), oil that is high viscosity at the operating temperature, something like 10w40 (notice the 40? – that’s the viscosity at operating temperature), could help fill the increased tolerances between mechanical parts. But at that point, your car’s engine is pretty much dead anyway and there’s no point trying to save it, and in some cases, it might kill the engine faster (turbocharged engines especially).
With that being said, I would still recommend using the exact motor oil that your car’s manufacturer recommends – nobody knows your vehicle better than the engineers who designed and built it.
Eddie is the co-founder of CarCareCamp.com, and the site’s primary contributor. Automotive repair has played a major role in his family for generations and he’s determined to continue the legacy further on. Under his belt, Eddie has a bachelor’s degree in Automotive Electronics Engineering and almost a decade of experience working as an electrician in a major semi-truck dealership in Europe.