Piston Slap: Inject Fuel Directly Into…Oil?

Sajeev Mehta
by Sajeev Mehta

Evan writes:


I have a piston slap question for a friend at work. She drives an ’11 Mazda CX-7 2.3. For over a year she has had an issue with fuel in the oil. Enough that the oil level has been as much as 1″ above the full mark on the dipstick as a result (oil level was checked after service, and frequently between services). This is noticed within weeks of service/oil change.

The issue seems to be worse with more short trips, and the car has been serviced as recommended by Mazda (or more frequent oil changes when warranty fixes attempted). The dealer has had the car repeatedly over the last year, and now continuously for over 2 months. They have replaced the HPFP 6 times as well as replacing the injectors twice. Leakdown and compression tests show no issues. Canada has no lemon law (just horrible binding arbitration), or the car would probably be a buyback by now.

The dealer has spent over 13k in repairs trying to fix it. They are at a loss, and Mazda forums haven’t helped, so I come to you and the B&B hat in hand. Also, even if they can fix it how much damage will so much fuel dilution cause? Should they demand and reasonably expect some sort of engine warranty extension?

Sajeev answers:

I am totally bummed to hear about your lack of Lemon Law-ing ability in this case. O, Canada!

I would seek more information on arbitration and contact Mazda Canada formally (AND via Social Media) to see if they’ll do anything. Sell this Mazda after the (possible extended engine) warranty expires…unless you’re thinking what I am thinking. Ya know, an LS4 swap.

Mmm, LS4-FTW…that would be so awesome.

(cue harp strings, dream sequence)

OH YEAH! Front wheel drive…with BALLS! Zoom-ZOOM-Zoom!

Ahem, now where were we?

Finding conclusive information on why fuel-oil dilution exists is tough via Google, but this SAE paper might contain the truth. Too bad I’m too cheap to buy it, too lazy to read and summarize for everyone’s benefit. Maybe some engineers with active SAE memberships can chime in here?

What say you, Best and Brightest? Time to get a lawyer?

Send your queries to sajeev@thetruthaboutcars.com. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

Sajeev Mehta
Sajeev Mehta

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  • Evan Williams Evan Williams on Aug 13, 2013

    I know I'm late to the party to be replying, but have some follow up on this. The dealer agreed to a buyout and an excellent price on a CX-5. I don't know the exact details, but it seemed to be an extremely generous offer. My co-worker is very happy with the CX-5 so far. I hope she remains so. I feel bad for whomever ends up with her old car.

  • Silviu Silviu on Apr 02, 2015

    I have exactly the same issue with my 2010 cx7.No issues at all for almost 3 years when the mazda did a free emission software update whilw a regular oil change. about 300 km later I found a pool of oil under my car.I checked the oil level expecting to see low level on the dipstick.To my surpise the oil level was so high,I could not believe.about 2 inches above max. no wander that the oil started leaking out of the engine.I contacted mazda right away,the car being under waranty. and from here on ,the nightmare started. -mazda investigated the issue and admited tah there is an issue with oil being contaminated with fuel -replaced the fuel pump.issue not fixed -replaced the fuel pump again thinking that the new pump is faulty.again no luck -replaced injectors.oops,issue still present.every 300 km summer drive oil level 1 inch above max level -mazda decided to replace the engine.again no luck after that mazda decided they do not knoe what to do anymore and also that this is not a real issue(the same non issue that made mazda to replace 2 fuel pumps,injectors and engine) When I told them that is to much of a coincidence that everithing started after the emission software update,they said that mazda do not have the old software version anymore. so for profesional mechanic that understand and know everithin and tend to downplay avery issue they do not know how to fix I,professional electromechanical navy enginer for 20 years I can tell them some secrets about WHY the oil level for an engine is important.WHY HIGH oil level can damage your engine.WHY a mixture of oil and fuel is not going to lubricate your engine animor but only wash it.and last but not least how much damage a contaminated oil that does not lubricate,is going to do to a high rev turbocharger.And on top of everithing,mechanics 101 it tells you how much of a fire hazard is running a car with high fuel contamination.Because more you drive,more fuel it gets mixed with oil And to finish this I ask the mazda professional:if a mechanic cannot find a solution to a problem he created,what is going to happen?.Because my dilemma now is this: I offer to pay 10000 dollars if mazda is going to fix the issue.Guess what: they have no clue how to do it.and like me(I am the lucky one in this history) there are so many other cx7 owners that been screwed by mazda ,blaming the owner for not doing the porper maintenance.because mazda not having a fix for this issue,they will not tell you that you have this problem,when they do the oil change.Unless you find it your self. So my advice:get a lawyer! )

  • JOHN One is for sale on an ebay car donation site.https://www.ebay.com/itm/305579991767?itmmeta=01HYHVJ49MCC6HEWQY5AX9MX85&hash=item4725fca2d7:g:k9cAAOSw5V5mThFw
  • Scott So they are losing hundreds of millions of dollars and they are promising us a “Cheaper EV”? I wonder how that will look and feel? They killed the Fiesta because they claimed that they couldn’t make a profit on them and when I bought the first one in late 2010 they couldn’t deliver the accessories I wanted for it! Then I bought a 2016 Fiesta ST and again couldn’t get the accessories for it I wanted. They claimed that the components were going to be available, eventually. So they lost on that one as well! I don’t care about what they say anymore. I’ve moved on to another brand.
  • Michael S6 CX 70 or 90 will not be on my buying list. Drove a rental base CX 90 and it was noisy and the engine noise was not pleasant. Ride was rough for a family SUV. Mazda has to understand that what is good for Miata isn't what we expect in semi luxury SUV. My wife's 2012 Buick Enclave has much better Ride and noise level albeit at worse gas millage. Had difficulty pairing my phone with Apple CarPlay
  • Michael S6 What is the metric conversion between one million barrels and the number of votes he expects to buy.
  • NJRide This could give Infiniti dealers an extra product maybe make it a sub brand