Case Studies

Mini Cooper – Engine Problem – Carbon Deposits On Intake Valves

Problem occurs with both "S" and non "S" models
Problem occurs with both “S” and non “S” models

Carbon Deposits On Intake Valves
As the largest Mini Cooper service specialists in Maine, at the Atlantic Motorcar Center we’ve noted a significant increase in late model Mini Coopers with cold start or cold running problems, even to the point of stalling, or Check Engine warning lights coming on.

We’ve found that many of these Mini Cooper direct injection engines suffer from an excessive carbon build up on the back of the engine intake valves.  The carbon build up can cause drivability issues such as stumbling, flat spots and lack of power, poor throttle response, or in extreme cases, internal engine damage.  In addition, Mini Cooper engine carbon build-up on the intake valves is commonly associated with an inconsistent idle and in some cases, a direct injection engine will not idle at all when cold.

The Cause
Due to stricter federal emission requirements, most manufacturers have switched to an fully closed emission control system that cycles the crankcase fumes back into the cylinders to be burned off. Also, oil from lubricating the valve guides can drip down the valve stem, and deposit on the back of the intake valves.

Carbon Coated Intake Valve
Carbon Coated Intake Valve

As you can see from the photos below, carbon build-up around intake valves in a Mini Cooper engine is a sticky coating of oil and fuel constituents, we’ve noted that this issue seems to be worse on the 2007 and newer models, but we have seen in as well on the earlier cars. Once formed, these deposits continue to grow, further coating the intake valves and has an extremely negative effect on engine performance.

Great idea for emissions, but certain driving styles lead to a rapid onset of this issue. Vehicles that aren’t driven for extended (20mins or so) periods at full operating temp are more prone to the issue. I.e. cold start and a 15 min drive to work then shut off until leaving work. The more often run and stopped away from full op temp the faster this issue develops. There seems to be no difference in manuals or autos.

The Fix
The Atlantic Motorcar Center has developed a very through cleaning process for Mini Cooper (and other models) with direct injection engines.  Our process safely removes the carbon build up and is significantly quicker and less expensive than removing cylinder heads and subsequently cleaning the valves (a common dealer suggestion).

Our process involves minimally invasive mechanical service work, and some special tools, which allow us to directly access, inspect and learn the intake valves.  The process removes all of the carbon build up and consistently returns good engine performance.  To de-carbon a Mini Cooper engine takes less than a day and the results are excellent – improved cold start operation, immediate throttle response and power return. Best of all, we can carry out this entire process for a fraction of the cost of other alternatives, and you’ll love the results, our 5 Star Service Rating speaks for itself.

How To Prevent Carbon Deposits On Intake Valves
An ounce of prevention is worth a pound of cure, so here is what you can do to help prevent this from occurring with your beloved Mini, BMW or other vehicle. How fast the intake valves get dirty does not seem to be a function of fuel quality. Rather, it appears to be influenced most by driving habits, and how often the engine oil is changed. Oil vapors and combustion byproducts that are drawn back into the intake manifold through the crankcase ventilation system seem to contribute most to carbon deposits on the intake valves.111

At the Atlantic Motorcar Center, our advice is to change your oil every 3,000 to 5,000 miles if you only do short trip stop-and-go city driving, or change your oil every 5,000 to 7,500 miles if you do mostly highway driving. If you want to minimize carbon buildup on the intake valves, don’t push your oil change intervals to 7500 miles or longer unless you are using a high quality full synthetic oil (which usually has less volatility than conventional motor oil).

We also recommend the monthly use of a fuel additive, like Lubromoly, or Chevron Techron, while these cars are direct injection, and as such the fuel does not inject onto the back of the valve, but rather in the cylinder itself, we’ve noted that cars using these products experience considerably less carbon buildup.

Questions, or if we can be of help in any way with service on your Mini Cooper, BMW, or other European (and now Japanese) import, please contact us. Our team of Service Specialists are here to help, for even the newest autos! (207) 882-9969.

Knowing, not just “doing”, that’s the Atlantic Motorcar Center way of life.

The Atlantic Motorcar Center Service Team


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