Doing the daily grind in your 4WD? Chances are it’s…

Carbon build up has been a life-long problem in petrol engines. Pick up a 70 year old copy of Popular Mechanics and you’ll find loads of info on de-coking an engine. Unfortunately, as technology has improved the issue has gotten worse rather than better, with modern diesel engines copping it worse than others. The term is a bit of a catch all, but the basic breakdown is a build-up lining the walls of the intake narrowing airways, gunking up sensors, and causing all sorts of issues with fuel economy and engine longevity. It’s an issue that commonly comes up with 4WDs that just do the daily-grind, or are rarely driven under load or for long distances at high speed. So if your 4WD is also the family wagon it’s more susceptible than the weekend warrior.

While older engines are mainly affected by spent exhaust gases being pushed back up through the inlet valve, modern ones are a little more complicated. The key factor is oil misted pressurised air being pushed through the crankcase on compression, up through the breather and back into the air intake. This oil misted air then mixes with hot gases flowing through the EGR valve and gums up everything it meets. The result is an intake system that struggles to move air freely and can lodge vital components open.

THE SYMPTOMS

When issues go wrong with your drivetrain most will present themselves immediately with huge power loss, excessive temperatures, or billowing smoke from the exhaust. A choked-up intake system will be a more gradual progression with the owner often not being aware anything is wrong until things reach breaking point.

There’s two main concerns when carbon builds up. The first, is a physical restriction in the intake itself. Imagine tapping up the end of your snorkel head smaller and smaller and you’ll get the picture. It can starve the engine of air causing issues with air fuel ratios, bad fuel economy, and excessive smoke from the exhaust. If the inlet is clogged enough it can also cause back pressure against the turbo and poor throttle response.

The other issue, is the EGR or inlet valves sticking open. As carbon deposits build up on these it can stop them sealing properly. It’ll allow the engine to suck in exhaust gas when it thinks it’s only getting fresh air, throwing fuel ratios out the window potentially melting pistons or cracking heads. In most cases, by the time you identify an issue the underlying cause is normally so far advanced damage has already taken place so sitting back waiting for symptoms is a huge gamble.

THE FIX

If you’ve got a diesel and haven’t done anything to prevent carbon build up it’s almost guaranteed your intake will be at least partially blocked, it’s as simple as that. To rectify this there’s a few ways you can go about it.

The first, and simplest, is a chemical clean out. If the vehicle isn’t showing any signs of excessive build-up such as poor fuel consumption or a lack of power, we’ll often use a Liqui-Moly product known as Pro-Line intake cleaner. It requires basic removal of air intake pipe work to gain access to the EGR system, then we’ll run the cleaning agent through to break down the build-up and flush it through.

If things have gotten beyond that stage, simple chemical cleaning often won’t be enough to get all the ins and outs cleaned, or to free larger deposits. When they get to this point it’ll require stripping the intake system completely off the vehicle and manually cleaning it inside and out to get it like new. In older diesels, it’s not too labour intensive, but modern diesels and especially V8 ‘Cruisers can be up to a full day in labour to get the job done properly.

THE VACCINE

They say an ounce of prevention is better than a pound of cure and in this case that couldn’t be closer to the truth. The fix all for all these issues is incredibly simple.

Fit a catch can.

Fitting a catch can when you start with a clean intake removes the oil-misted air from the intake, giving the carbon nothing to catch on and build up. The result is a free flowing EGR system, no gunk on the lip of your valves, and no restrictions throughout the manifold with absolutely no side effects and completely legal. Don’t go chucking any old eBay catch can on though. Cheap alternatives often have very little baffling to actually remove the oil from the air, making them just a fancy looking hose. They can also have restrictions as well which will build up pressure inside the engine and start punching oil seals out. A quality unit will cost a few hundred dollars installed, but WILL save you literally thousands of dollars over the life of the vehicle. And that’s smart money in anyone’s books.