Piston Slap: A Leaky Rear Goes Unnoticed

Sajeev Mehta
by Sajeev Mehta
piston slap a leaky rear goes unnoticed

Drake writes:


I have a 2007 Fusion with the 3.0 Duratec V6, with 83,000 miles on it. I have owned it since new and 90% of the miles are long highway drives. I have recently discovered that there is an engine oil leak. I have put the engine oil dye from Ford in it to try to pin point where the leak is coming from. It is a small leak, takes a while to get noticed (when the oil finally makes it’s way to the exhaust and smokes a bit).

Local Ford dealer does not have a clue, I have called other larger dealers in the area and had them check for service bulletins and asked if anyone has come across a similar problem and what it may be. No luck. Best that I and a couple of very good mechanic friends can figure is that a head gasket might be leaking.

So, I have traversed the Internet looking for and information about this problem when I came across one of your articles. Thanks!

Sajeev Answers:

While I appreciate your searching found our corner of the autoblogosphere (woot!) this is one time where the “been there, done that” crowd in a Fusion-specific forum would help. This automotive dilemma is tough to “armchair” an analysis: visual inspection is needed. I could go for a Fusion in my garage right now, to see where the usual suspects (pertaining to oil leaks) live relative to your car’s exhaust system.

But I doubt it’s the head gasket. If it was, you’d notice more than a few dabs of oil burning on the exhaust: the head gasket material around oil passages isn’t (normally) close to the end of the engine block, that’s usually reserved for the cylinder walls. Therefore, a spewing head gasket is more likely to lose compression and/or burn oil. Which would be far more annoying. Best and Brightest, am I off base?

I blame the rear main seal. This little part is a rather huge PITA to set right, there’s a transmission/transaxle blocking access. More to the point, I’ve seen many cars at this mileage suffer from this condition. Plus, front-wheel drive platforms with two banks of cylinders (i.e. a V6 engine) must route the exhaust in “compromising” positions around an engine and transmission, a leaky rear main can easily drip over an exhaust pipe, move back (at highway speeds) to the pup-cats (the first set of catalytic converters) and disappear into a puff of smoke. And you’ll never see the dye, either.

My advice? Have a look around the transmission’s bellhousing for the “dye”, and just deal with it. Rear main seal leaks are normally trivial, not worth the effort of fixing until transmission needs refreshing. You know, if you choose to not pull a Mike Rowe, preferring to not “swap your ride for (another) Fusion.” to keep your ride for that long.

Send your queries to mehta@ttac.com. Spare no details and ask for a speedy resolution if you’re in a hurry.

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2 of 18 comments
  • DIYer DIYer on Dec 15, 2010

    I agree with dolo54, Educator(of teachers)Dan, and crosley, that it might be time for high-mileage oils, or snake oil, that contain seal conditioner. I have a 1993 Firebird Formula LT1 that developed an intake manifold seal leak at about 120K. Oil was running down the back of the motor onto the flywheel cover. I used some Lucas Engine Oil Stop Leak for a couple of oil changes: http://www.lucasoil.com/products/display_products.sd?iid=83&catid=7&loc=show I was running 5W30 Valvoline synthetic, and now I run 10W40 Valvoline high mileage synthetic blend, and the leak has stopped. I do know exactly what the problem is, and at some point, I'll need to do a proper fix to the gasket. I do get a little less mileage running the thicker oil. The vehicle has 155K on it now. I would try something like this before tearing anything apart.

  • Fusion78p Fusion78p on Dec 30, 2010

    Thanks for the replies to my dilema! Here is what I have found out We have ruled out the rear main seal leaking. And the head gasket is fine (!!!). My worst fears have been quelled. After a bunch of a elimination process we think we have found the problem. There is a spacer or extension that is between the block and oil pan. That spacer or extension is where it appears to be leaking from. And it is getting worse. The oil pan looks to be fairly easy to remove but we can't see all of the spacer deal and so I pose the question: anyone had to remove this part? Or how much is envolved in removing it? I cannot find a decent schematic or picture of the engine that shows this part. For the record the spacer is sealed with silicone. By the way I did have 5W-30 in the engine just before this oil change. I had heard that changing the oil from what is recommended is not such a good idea and may have caused the engine to start leaking. I personally think maybe the Mobile 1 full synthetic oil I ran for a while might have caused the PCV to start sticking which in turn caused the engine to find a weak link to relieve the crank case pressure. Probably way off base but I think this is what started the whole mess. I do agree that running a slightly heavier oil when the miles rack up is no sin either. We changed the oil and filter this past Monday evening (Motorcraft 5W-20 syn blend) to get back to the starting block and rule out everything possible. PCV has been replaced as well. Any help would be great! Thanks!

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