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Oil for high mileage engine

Which oil should I use in my high mileage engine

Lots of people want to know what’s the best oil for a high mileage engine. Should you stick to the original recommended viscosity or use a heavier oil in a high mileage engine? What if you’re engine is burning oil? Should you add an oil stabilizer to a high mileage engine? If so, should you add the oil stabilizer to the original oil or add oil stabilizer to a thicker oil?

The easy answer to what’s the best oil for a high mileage engine is pretty easy.

Use the oil viscosity recommended by the vehicle manufacturer. Using a heavier weight oil in a high mileage engine may reduce oil consumption, but it’ll also cause faster wear. So you won’t have to worry about high oil consumption because you’ll literally destroy your engine faster.

The same holds true with adding an oil stabilizer to the oil on a high mileage engine. Don’t do it.

Here are all the reasons why you should never use a heavier weight oil on a high mileage engine or add oil stabilizer.

If your high mileage engine has variable valve timing or gasoline direct injection, using the wrong oil can destroy it or at least cause a check engine light.

Engines now have variable valve timing (VVT), gasoline direct injection (DI), and turbos that place different demands on oil. For example, DI requires fuel pressure of up to 2,000-psi. So your car has two fuel pumps—one in the tank to deliver fuel to the engine pump and a second high pressure pump. The high pressure pump runs off the triangular lobe on the camshaft. If you use the wrong oil-either the wrong viscosity or the wrong service rating- you can damage the camshaft. And when it comes to turbos, you need an oil that won’t break down under high heat conditions. Plus VVT has it’s own unique operating conditions. The engine computer changes valve timing with a hydraulic actuator. The actuator moves based on pulsed oil pressure from a pulsing solenoid. The computer commands valve timing changes based on factory recommended oil viscosity. Change to a different viscosity or a different service rating and the actuator won’t respond properly. That’ll set a check engine light and affect engine performance and emissions. AND, because it’s pulsed, the oil can develop air pocket and foam. Foam doesn’t cool metal – it actually insulates, so the oil runs hotter and degrades faster.

If your engine doesn’t have VVT or GDI

So you don’t have to worry about VVT mechanisms or high pressure oil pumps. But your high mileage engine has more wear on the piston rings and it’s generating more blow-by gas. More blow-by means more acid, soot, corrosion, varnish, and sludge formation in the crankcase and throughout the entire engine. Switching to the same viscosity synthetic oil is one good option. It has a more robust additive package to neutralize the contaminants and keep your engine cleaner. It flows faster at startup and builds pressure more rapidly. So it reduces cold startup wear and actually prolongs the life of your engine. The extra anti-wear additives offer greater protection against further wear.

But switch to synthetic oil for the prolonged engine life benefits, not extended oil changes. Because you STILL have to change synthetic oil at the same intervals as conventional oil. You cannot override the car makers recommendations. So it’s going to cost more. But your engine will last longer. You do the math.

What about fixing a low oil pressure issue on a high mileage engine?
What about fixing a high oil consumption issue on a high mileage engine?

Many wanna-be mechanics think that older engines need a higher viscosity oil to combat low oil pressure and engine wear. WRONG. Higher viscosity oil creates higher pressure because it resists flow. You may think you’ve solved your low oil pressure problem. But you’ve created another in its place. Less flow means higher oil temperatures and that results in more rapid oil breakdown. More resistance to flow also increases heat buildup from friction. So your engine will actually run hotter and get worse gas mileage. The lower flow rates and higher temperatures cause more rapid additive breakdown, so you’ll actually get less protection against metal wear and deposit formation (sludge). In other words, what you gain in oil pressure and lower oil consumption, you’ll pay for in dramatically shorter engine life.

The same holds for oil stabilizers

Oil stabilizer is basically viscosity index improver. Look at how thick it is coming out of the bottle. It also has an additive to improve surface tension so it sticks to metal parts better. Great, as far as it goes. But it doesn’t combat any of the other issues in a high mileage engine.

Instead of using a higher viscosity oil or an oil stabilizer additive, switch to a high mileage synthetic oil. High mileage oil contains film strengthening additives to improve ring sealing and oil pressure. And some brands also include seal conditioners to soften stiff seals, as well as extra anti-oxidant, anti-corrosion, anti-wear, and detergent additives to handle the additional crud in the crankcase. So you get all the benefits without increasing oil viscosity.

When should you change oil?

Many owners of high mileage cars experience high oil consumption rates. They think that since they’re adding oil on a regular basis, they don’t have to change their oil. Wrong. As mentioned earlier, high mileage engines create more blow-by and acids which uses up the oil’s additives faster. Add to that the fact that burning or leaking oil means you’re probably running the engine when it’s low on oil. Running a quart low puts tremendous stress on the remaining oil, and it was already under stress due to the high mileage issues. Adding more oil doesn’t come close to bringing the remaining oil back up to recommended additive levels.

If anybody tells you how long you can go between oil changes, but they don’t ask about your driving habits or how often you have to add oil, they are full of it. It’s that simple. The way you drive your car impacts how long the oil will last. NOBODY can get you an oil change interval without knowing that information.

Frequent cold starts dump raw fuel into the crankcase, diluting the oil and causing more cold start-up wear. Unless you drive the car for long periods after a cold start-up, that excess fuel and water will form sludge. Read this quote from The Center for Auto Safety:

“The Center for Auto Safety (www.autosafety.org) has logged over a thousand complaints about oil sludging problems from motorists who thought they were following the service intervals recommended in their owners manuals but ended up with a crankcase full of sludge.

Extended oil change intervals of 7,500 or 10,000 miles or more are based on ideal operating conditions, not the type of short trip, stop and go driving that is typical for many motorists. Consequently, most drivers should follow a “severe” service maintenance schedule rather than a “normal” service schedule to protect their engines.

Severe service includes:

* Most trips are less than 4 miles.

* Most trips are less than 10 miles when outside temperatures remain below freezing.

* Prolonged high speed driving during hot weather.

* Idling for extended periods and continued low speed operation (as when driving in stop-and-go traffic).

* Towing a trailer.

* Driving in dusty or heavily polluted areas.”

Some engines, such as diesels, suffer more blow-by than others and typically require more frequent oil and filter changes. For most passenger car and light truck diesels, the oil should be changed every 3,000 miles without exception — especially in turbo diesels.

Turbocharged gasoline engines also require more frequent oil changes because of the high temperatures inside the turbo that can oxidize oil. A 3,000 mile oil change interval is also recommended for all turbocharged gasoline engines.

©, 2015 Rick Muscoplat

Posted on by Rick Muscoplat

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