(Apologies in advance for the lengthy post.)
2006 Infiniti G35 Coupe, 6-speed manual, 112K miles. I bought the car from a friend when it had about 50k miles. He had the car for the previous 30k miles. We are both sticklers for maintenance and both used synthetic oil (typically Mobil 1) exclusively.
This car has never burned or leaked a drop of oil.
I took the car in to Kwik Kar a couple of weeks ago for an oil change. While I was there, the mechanic recommended an engine flush. (I've since learned that this isn't really recommended for such a high-mileage engine.), as well as a power steering flush and something else I can't remember. (The receipt is in the glove box of the car, currently sitting at Kwik Kar.) This is the type of flush that involves flushing the oil with some sort of additive / solvent / ??, not the one where some mysterious substance is injected into the intake.
2-3 days after the flush, I noticed an obnoxious rattle when starting the car. Over the next couple of weeks, it got progressively worse. I took the car back to the same Kwik Kar. The (different) mechanic took me into the pit and said that the noise was coming from the catalytic converter. To me, the noise - insanely loud under the car - seemed to be coming from forward of the bell housing.
The mechanic noted that the oil was low (and very dark considering it had about ~1000 miles on it). There was no sign of a leak. I've also not noticed any smoke (of any color) from the exhaust at any time.
They added some sort of additive - white bottle with an STP logo - which they thought would help the noise. I'm not a fan of snake oil "solutions." I also asked how, if the noise was coming from the cat, an additive was supposed to help, but didn't get a comprehensible answer. (It didn't help.)
That was about 1 - 1.5 weeks ago. This morning, the rattle on start was very bad, and very noticeable when driving up to about 3k RPM. It is definitely RPM-related, not speed related. I (unwisely) decided to drive it back to Kwik Kar.
The Fun Part
The engine popped and vented several quarts of oil on the highway, and came to a thankfully drama-free halt. I had the car towed back to Kwik Kar (giving them a chance to look at it first).
I was told:
There's no way an engine flush will cause an engine to blow. This seems odd to me since, if they flushed gunk out of the engine, it would wind up in the oil pan. There, the oil pump could pick it up, potentially clogging oil passages pretty much everywhere.
Since I'd driven the car ~2k (total) miles since then, the flush couldn't have caused the problem. The mechanic (third one I've met) said I should have brought it back when it started making the noise. I pointed out that I had brought it back.
The mechanic that initially worked on the car was off, and should return tomorrow.
In short, they were not very encouraging or helpful. I have little confidence that the original mechanic is going to admit any fault.
I would readily admit that some times things just happen on high-mileage car, but this thing has run like a top for the entire time I've owned it. It's never had an engine-related squeak or rattle. It seems highly unlikely that this would just magically happen following Kwik Kar's service.
Thoughts? What actions should I take at this point? A re-manufactured engine for this car is upwards of $3k, not to mention labor cost.
Kwik Kar is denying responsibility, and wants ~$9800 to replace the engine with a used one that has over 90k miles on it, claiming a 30% labor discount. I find it odd that they would offer a labor discount if they don't believe they're at fault, but such is life. I am disinclined to let them touch anything. (Their diagnosis is a thrown rod.)
City Garage quoted $7500 for a similar high-mileage engine. (I've had cars in there before and have always had a great experience.) The labor portion is about $2k (USD). After perusing the service manual, that sounds like a good deal, but the engine price is significant. I've found remanufactured engines online for $2k-$3k, but I haven't found a shop that's willing to install a customer-provided engine. So, I can save several thousand dollars, but it looks like I'll have to do the labor myself. (I've swapped engines before, but not on anything this complicated.)
If anyone knows of a shop in north DFW (Plano / Wylie area) that would be willing to take this on (install an engine I provide), please speak up!