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really awful
Typical Repair Cost:
No data
Average Mileage:
123,653 miles
Total Complaints:
1 complaints

Most Common Solutions:

  1. replace chain tensioner (1 reports)
2004 Mazda MAZDA6 engine problems

engine problem

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2004 Mazda MAZDA6 Owner Comments

problem #1

May 132015

MAZDA6 GT 3.0L Duratec V6

  • Manual transmission
  • 123,653 miles


This Duratec V6 3.0L is relatively reliable, but appears to have been under-engineered in at least two respects for our vehicle (VIN to follow). it was a copper 5MT GT hatch and had lived life as an enthusiast car (colour, transmission, and Magnaflow exhaust and AEM intake installed)

we purchased the car at 170,000km for a pittance, two years ago (fall 2013) The previous owner had it for sale as he couldn't get it running above 3000rpm. It would start and idle fine, but it wouldn't rev beyond 3000rpm. above 2000rpm, it was laboured and generated zero power, and if you downshifted, it would instantly slow down to 3000rpm max.

Bottom-line, the Timing Chain tensioner is under-engineered, big-time. It fails prematurely, and my hypothesis is it does so more rapidly in cars with 5MT and especially those that are aggressively driven, with more shifting at higher RPM (thus more stress on the tensioner). our car's tensioner had allowed the timing chain to slip a few cogs. to change it requires ripping the heads off the car and basically opening the entire thing up. major pain in the ass.

then, I figured all was fine, in early 2015, at approx. 190,000km I decided to put some money into the car as the vehicle configuration (5-door hatchback) is so practical. New shocks, suspensions, motor mounts, new hood and fender, partial paint job, and some other wear parts.

May 2015, driving home, low oil pressure light flickering at a red light. WTF? get home in 5KM, and crankcase barely shows anything on the dipstick. ends up the motor is 3L down from 6L crankcase capacity.

Then, TWO MONTHS of diagnosis as follows:

front bank plugs fouling, mainly center cylinder #5. going through plugs weekly, blowing blue smoke out the back we disconnected and plugged off the intake manifold breather hose (part # 13-740) still oil fouling, so opened up the intake manifold, did some research online. found issues with the PCV, with others on Ford forums even going so far as to hook up two PCV valves in parallel so if one fails, you still have the other good one.

It appears the PCV valve, when it fails, causes CATASTROPHIC ENGINE FAILURE RAPIDLY BY SUCKING OIL OUT OF THE CRANKCASE, and into the combustion by some means. within 5-10 miles of driving you are down from full oil capacity to dangerously low. Driven enthusiastically, as I did the car, caused major engine damage to valve train and most alarmingly, the rings. It appears oil starvation is worst and first apparent on the front bank, thus the heavy damage to the front bank of cylinders with little effect to the rear bank.

the heavy oil ingestion due to PCV failure then has a possible (I'm not certain of this) spillover effect into failure of the EGR valve, we had to replace this expensive part as it appeared to be sending heavy oil back into the intake.

scanning the OBD2 revealed many P171, P300 P304, misfire, lean burning, random misfire codes, misfire of #4 and 5. This has nothing to do with the intake gaskets or engine timing etc etc etc.

it appears to be heavy oil ingestion as a result of burned piston rings in the front bank due to oil starvation of the front bank, resulting from PCV valve failure causing engine oil starvation and EGR failure.

This is an abominable and abysmal engine design. routine failure of a $5 part should NOT take down a motor. a routine failure should NOT take down a 747. If the PCV is so poorly designed, then it should be a routine service item every 30K miles AND/OR TWO PCV should be installed in parallel so that one failure still allows the other to operate as a fail-safe until service can replace one. THIS IS VERY POOR ENGINE DESIGN THAT A MINOR AND INEVITABLE PART FAILURE CAN TAKE DOWN THE ENTIRE MOTOR WITHIN 10 MILES OF THE PART HAVING FAILED!!!! completely unacceptable.

We have now changed the PCV and the EGR Valve I can't drive 5 miles before the plugs get all fouled up again. we checked compression the front cylinders were 60, 100, 80PSI for cyl 4-6 with 5W30 oil when the motor was hot. I drained the 5W50 as specced, and refilled with 15W40. I've purchased the heaviest weight, 20W50 Castrol GTX in order to maintain compression and retest to see how much improvement can be obtained with heavier-weight oil.

The breather hose is going to be reconnected tonight. having had it opened, caused smoke to waft out from the motor at red-lights, and oil to be consumed (or lost, rather).

any owner of the v6 3.0L Duratec would be well advised to change their PCV every 30K miles, or sooner. the part is dirt cheap and failure of this 20 cent part will doom your motor.

Any owner of a 5MT should be sure to double-clutch downshifts and try to rev-match shifts as much as possible, to reduce strain on your timing chain tensioner. basically this part is under-engineered and is not designed to take the stress of this motor. Given enough time, the chain tensioner will fail on all automatic transmission mazda6s, but my guess is aggressively-driven 5MT cars will show the earliest failures due to higher-RPM shifts placing more strain on the tensioner.

LEMON ALERT due to poor design LEMON ALERT due to routine, expected failure of basic, cheap part being able to cause catastrophic failure of the motor with no notice and very little time/distance required before irreversible engine failure has occurred.

- , Vancouver, BC, Canada

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