Why Honda & Acura Can't Fix Their Shaky V6

Honda Odyssey 2015 6 photos
Photo: Honda
Burned Piston RingsPistons can be reusedRear Cylinder Head With VCM ManifoldAll this work for a few ringsThis gap is where oil moves north
Sometimes, the road to hell is paved with good intentions. So, what happens when one of the world’s largest automakers is caught between a rock and a hard place?
A few weeks back I changed the spark plugs and ignition coils on my friend’s 2013 Honda Odissey. It had a slight misfire that was cured by the tune-up, but a week later the symptoms returned. Just as before, the plugs from the rear cylinder head were crusty and fouled.

Perplexed by this, I discovered similar complaints from owners of the Pilot and several Acura crossovers. This led me to look for an underlying defect in the manufacturing or service intervals of the J-Series of engines, and the truth is stranger than fiction. The issues plaguing these popular models are caused by the never-ending quest for fuel mileage.

When the government updated the Corporate Average Fuel Economy laws in 2007, many manufacturers rushed to introduce cylinder deactivation. This is done by restricting oil flow to the lifters and disabling the ignition, and it works great in a laboratory. But in the real world, owners began to experience misfires at around 60,000 miles.

This gap is where oil moves north
To understand the issues, a bit of history is needed for context. Back in 1937, Soichiro Honda opened his first business making piston rings for Toyota. Honda’s rings were so well-made that Toyota bought the company outright after the war. Complacency has a way of creeping in over the years, and the piston rings became the scapegoat for the misfires. Officially, Honda stated that the rings were rotating on the pistons when running in Eco mode. But the real damage happened years ago when the Variable Cylinder Management system was on the drawing board.

Their goal was to maximize the fuel economy of the Odissey and the Pilot by disabling the rear three cylinders. With the intake and exhaust valves closed, no air was supposed to get in or out of the cylinder. However, Honda’s low-tension piston rings had other intentions. In the lab, engineers accepted that some oil would seep past the rings. It would be burned off once everything was up to temperature, but they didn’t consider the damage done by short trips.

Because the cold oil was too viscous, it clogged the drain back holes in the rear pistons to form a ring of sludge around the rings. Instead of doing their job, the oil rings were held hostage by sludge, and this allowed oil to flow almost freely into the combustion chamber. If the VCM system is active, the rear pistons are subjected to torture. The most logical fix would be to disable the system to keep the car in V6 mode, but that’s not what happened. Instead, Honda extended the powertrain warranty to 8 years of the purchase date, regardless of who owns it now.

All this work for a few rings
Step 2 was a Technical Service Bulletin recommending the replacement of piston rings on the rear bank. This means a technician must disassemble your engine, and the only new parts you receive are worth a few dollars. New rings will solve the problem, for a few months. Once they are broken-in, the rings realize that their predecessors trashed the cylinders before moving out. Oil comes back to the party, and it builds up until the spark plugs are fouled out.

This has led many dealers to give their customers free spark plugs with every oil change, a quick fix that doesn’t address the problem. A redesign in 2018 has addressed the issues, but many owners are unhappy. The reason why VCM can’t be disabled by Honda is that doing so would be viewed as tampering with fuel economy (CAFE) laws laid out by the government. This would expose them to litigation the likes of dieselgate, and therefore Americans love their elected officials.

Even if your car doesn’t have symptoms, several aftermarket vendors have developed VCM disabling modules, and I highly suggest one if you plan on keeping the vehicle. Obviously, there is much more complexity to this situation, as it has the potential to ruin resale values for millions of owners. So stay with us for all of your automotive insights.

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