bought this MDX new in april 2014 and it has been the most boring car i have ever owned, which is a compliment. 138,400 miles now, 3.5 V6 with VCM (the cylinder deactivation that shuts off the rear bank on the highway).
two things lately. it is using about a quart every 2,000 miles, it never used to use anything between changes. and last week the check engine light flashed on I-485, code P0304, cylinder 4 misfire. the shop pulled the plug and it was oily and fouled. new plugs all around, light is off.
everything i read says VCM is the reason, the rear cylinders sit deactivated, oil gets past the rings, plugs foul. people sell plug-in boxes that keep VCM from ever turning on. is it worth it at this mileage or is the damage done?
i spent six years at a Honda store in Tustin before Lexus, so i have pulled a lot of those plugs.
your symptoms line up with what we saw. on the J35 with VCM the cylinders that deactivate are the ones that load up with oil first. a disabler will not unstick rings that are already carboned up, but it does stop the problem from getting worse, and a lot of owners report oil use dropping a bit after a few thousand miles of the engine running on all six.
two cautions. you will lose 1 to 2 mpg on the highway. and if you still have any warranty or plan to sell it to a dealer, remove it first. some service advisors will note it.
before buying anything, ask your shop to look at the front and rear engine mounts. on these the active mounts work hard to cancel the vibration when VCM kicks in, and a soft mount makes the switch from 6 to 3 cylinders feel like a shudder.
our old 2012 Odyssey had the same thing. we put one of the plug-in boxes in at about 120k, it is a little module that plugs into a sensor connector under the hood. oil use went from a quart every 2,500 to maybe half that. we traded it at 160k and it still ran fine. not science, one car.
update, had the independent shop look at the mounts. rear mount is torn, front is ok. $410 for the rear one installed. they also said the oil consumption number is not crazy for 138k and offered to do a proper consumption test (fill, seal the dipstick, drive 1,000 miles, measure) for $60.
ordered one of the disablers, about $90. will report back.
following this. my brother has a 2016 Pilot with the same engine and the same quart habit. he keeps a jug of 0W-20 in the cargo cubby under the floor and calls it the car's coffee. i will send him here.
three weeks and about 1,900 miles in with the disabler. results:
oil down maybe a third of a quart on the dipstick over that stretch, so better than before but not fixed. highway mpg went from 26 to 24.5 on my commute up to Mooresville. no flashing lights. the shudder at 45 mph is gone, which i think was the mount more than VCM.
for anyone with a 2014 to 2016 MDX checking for open recalls or service bulletins on this engine, the owner section on acura.com lets you put in the VIN. mine had none open. keeping it till 200k out of stubbornness.
