The Italian Tune-Up

As frequently as possible, my father used to find an excuse to take my grandmother’s car out for a drive. Grandma drove a Buick Park Avenue Ultra, with a supercharged V6 engine and velour headliner.

“Mom, I’m going to take the kids to pick up some milk from the store in your car, okay?”

“Sure, hon!”

Then, dad would buckle eight-year-old me and my six-year-old brother into the back seat, before flogging this bloated, geriatric Buick to kingdom come on the expressway. Visits to the redline came in succession as the gelatinous tarmac-tub surged along, its supercharger whizzing as the too-constricted exhaust hissed loudly beneath.

“Boys, this is good for grandma’s engine,” dad would tell us.

“Grandma doesn’t drive this car very hard, and the engine is all full of gunk. I’m cleaning grandma’s engine for her.”


We’d return some questionable amount of time later, milk in hand, hiding our grins under a strict order of silence. Dad’s secret engine-cleaning procedure was safe with me and my little brother.

This was many years ago, and that Park Avenue Ultra has since been recycled, melted down, and turned into bed-pans and table legs and cheap Chinese lawnmower parts. But at least it died and went to land-barge heaven with a squeaky-clean and gunk-free engine – according to dad.

Was he right? Can you actually “clean” an engine with hard driving? Can you evacuate the inevitable build-up of carbon and gunk from an engine with hard use, presumably incinerating the nasty deposits and blowing them out the tailpipes and leaving a cleaner and better-running engine behind?

To help answer this engine, and shed some light on an age-old practice, I spoke to Eric Kalberer, a Product Application Specialist for Shell Global Solutions, as well as Sarina Arnold, Shell Fuels Scientist Americas, Product Management & Deployment.

We’ll also hear from Daniel Grenier, Manager of Technical Support for Mazda Canada.

What is valve gunk? Varnish? Carbon? Sludge?

Let’s start with a look at what sort of deposits form in an engine, where they form, what they might be called, and where they come from.

“Generally speaking, throughout the service life of a gasoline engine, there will be some build-up of sludge, varnish, and deposits in different areas,” Sarina Arnold explains.

“Sludge is generally the material that turns the engine oil from honey colour (when fresh) to dark brown, or black. Engine oil contains an additive called a dispersant which helps keep the sludge suspended or dissolved in the engine oil – but if too much sludge forms and the dispersant is overwhelmed, it can lead to the sludge settling out in different areas of the engine, primarily where it’s cooler.”

Sludge tends to be sticky and can stick to different parts inside of an engine. When it does, it eventually leads to a thin layer of so-called varnish on certain parts. Thicker and darker deposits form when the varnish builds up, possibly as a result of further heating and oxidization of the sludge that sticks to hotter parts of the engine.

So, sludge is the foundation, and enough sludge can turn into varnish – which could also be called gunk.

But what about carbon?

“Sludge, varnish, and deposit formation occur as a result of the combustion process within an engine, and the degradation of engine oil over time,” explains Eric Kalberer.

“Indeed, they are made of carbon – though that’s oversimplifying. Actually, they’re carbon-based because they can also contain hydrogen, sulfur, nitrogen, and oxygen – among other things. They are a complex mixture that results from the by-products of combustion, moisture, and engine oil. As these accumulate and circulate around the engine, some help accelerate degradation of the engine oil, and eventually cause the engine to get “dirty” with varnish or deposits. For that reason, it’s important to use fuels and lubricants that meet the standards specified by the manufacturer and to follow the recommended service intervals.”

The gist? Whether you call it carbon, gunk, sludge, varnish, or something else, each term refers, loosely, to a build-up of potentially harmful substances that will take up residence within your ride’s engine.

Where are these deposits found?

“First, sludge accumulates in the engine oil where it is suspended by a dispersant so that it can be filtered by the oil filter, and not accumulate in the engine,” Arnold says.

“This is one of the primary drivers for changing the engine oil and filter following the manufacturer’s recommendation. Once any sludge, varnish, or deposits form in the engine, they can appear in many places.”

But what forms where?

Arnold explains, “Varnish and deposits are generally found in hot spots – places within the engine that are closest to the combustion process like pistons and rings. Sludge is generally found in cooler areas of the engine where any of the material that forms is not suspended in the engine oil and can settle out and stick, like the oil sump or the valve cover. A newer phenomenon, found in direct-injection engines, is to find deposits on intake valves, where they were once cleaned in port-fuel-injected engines by the fuel additives found in high-quality gasoline.”

Mazda’s Daniel Grenier adds, “Carbon deposit build-up, on the backsides of intake valves, occurs due to many factors such as fuel quality, oil quality, spark-plug replacement”.

Today, deposit build-up on intake valves of direct-injected engines remains a well-documented issue, though automakers are advancing measures used to help mitigate it.

How can the deposits be stopped?

“The extent to which these bad actors accumulate depends on a number of variables, including engine design, operating conditions, and the fuel and engine oil used,” Kalberer explains.

Grenier adds, “In addition to fuel quality and driving habits, valve and injection timing are key factors in carbon build-up. Additionally, software plays a huge role, the PCM will adjust as needed to lessen the impact of the carbon build-up. Carbon will continue to form until it becomes severe enough to create driveability issues and trigger the MIL (malfunction indication lamp, or the Check Engine light).”

Though modern gasoline direct-injection (GDI) engines are more prone to deposit build-up on their intake valves, proper maintenance and use of quality fuels and gasoline are typically sufficient to fend it off for the life of an engine.

Modern engines are also designed to resist this build-up, provided they’re maintained properly.

“Part of that design is a specification that ensures the engine oil will lubricate the parts needed and prevent the build-up of bad actors that can diminish engine performance,” says Kalberer.

“Service intervals are developed to ensure that the engine oils present are capable of doing the work to protect the engine. Lastly, oil formulating continually evolves. Shell has continually risen to the challenge in an industry where most modern, gasoline vehicles require semi-synthetic or synthetic engine oil capable of handling ever-higher engine temperatures and protection, even at low viscosities.”

So, according to our experts, it’s not a regular “flogging” of an engine, but rather a strict adherence to maintenance schedules that’ll work best to keep things squeaky clean.

Keep it clean

“The best way to keep an engine clean is to utilize the fuel, engine oil, and service recommendations provided by the manufacturer,” says Arnold.

Grenier adds, “There is no secret formula – but fuel quality, driving habits, and following the prescribed maintenance schedule will help avoid costly repairs later.”

There might be another trick worth considering in the quest to keep your powerplant clean, too.

“It’s not generally good practice to ‘flog’ a vehicle, which could result in unnecessary wear and tear,” says Arnold. “It is, however, a good idea to take vehicles that are typically driven short distances at low speeds out for some longer drives to get the engine up to a normal temperature regime. Not only does this better circulate the engine oil and additives through the engine to clean and protect it, but also helps to move the water out of the engine oil that builds up when cars run often, but don’t heat all the way up. When water builds up in engine oil, it can result in the formation of organic acids that lead to corrosion and oil thickening.”

In other words: “Cars do need to be driven at operating temperatures for a stretch of time to allow contaminants (fuel, moisture) that accumulate in the oil to burn off,” says Grenier.

But can I actually “Blow out the carbon”?

Can you actually “blow out the carbon” from an engine, or, more generally, use full throttle application to clean the inside of the engine like my dad used to do in my grandmother’s Buick?

Kalberer doesn’t think so.

“The logic for cleaning the carbon out of an engine is seated back in the days of carbureted engines, which were less precise than the current fuel-injected engines at metering in gasoline. There was generally some excess gasoline in these engines that would result in a build-up of “carbon” on valves and pistons that could gum them up. As legend has it, burning it off meant running for an extended time at highway speeds to get engine temperatures and airflow high enough to ‘clean’ off anything that could gum up the carburetors.”

Fast forward to today, and this is old logic best left for the history books.

“Engine designs haven’t been carbureted for more than 30 years,” comments Arnold. “Modern vehicles don’t gum up the way they did back then, including your grandmother’s 90’s Buick.”

Grenier adds, “Again, leaner and more carefully controlled fuel mixtures on modern engines are generally cleaner than yesterday’s engines.”

What’s the best way to keep an engine clean?

I asked each expert what the best and worst things a driver could do to for the cleanliness of a modern engine.

“The best way to maintain a clean engine is to use a full synthetic motor oil, use a high-quality gasoline, and maintain service at the intervals recommended by the manufacturer,” say our Shell experts. “This is a holistic approach to good vehicle maintenance for a long life.

“The worst thing one can do is utilize products that don’t meet the manufacturer’s recommended specifications, or to extend the mileage between oil changes beyond the service recommendation,” Kalberer adds. “That is a sure-fire path to premature engine performance and durability issues”.

Grenier adds, “Routine maintenance (following the manufacturer’s recommendations), use of name-brand high-quality fuels, high-quality oils, and regular highway runs to heat up the engine and exhaust to burn off accumulated contaminants are all important to keeping your engine running in good order.”

In summary, though a good full-throttle romp probably won’t hurt your modern engine, it won’t clean it, either – and you can’t actually blow any sort of deposit out of your modern engine with heavy throttle application. Proper maintenance; taking a long drive every so often if you usually don’t; and the use of proper fuel and oil can go a long way to extending the trouble-free (and gunk-free) life of your ride’s mechanical heart. Follow those steps carefully, and the design of your engine will likely take care of the rest.

Can you really “blow the carbon out” of an engine? 11/19/2018 10:00:00 AM