willie hernandez

Hi,
I have a 2007 Boxster S with 131K miles! It has always put out some white smoke and drops of oil on start up. Once warm, no smoke. It uses about 1qt of oil every 1500 miles. Lately, it has been throwing the P0431 Warmup Catalytic Efficiency Below Threshold Bank 2 code. I took it in and they replaced the AOS. Twice. It still smokes and spits small amounts of oil, but it's too soon for me to ascertain how much oil its burning. As a diagnostic tool, my indy shop took off the exhaust, waited overnight, and noticed there was oil weeping (I assume exhaust valves) in the morning on all cylinders. According to them, there also was oil in the intake in the morning. I'm now left with the promise of a valve job and possible engine rebuild. **Sarcastically** Luckily, my engine is SUPER cheap to rebuild and there are many options for rebuilding the engine.
My questions are these:
1. Is the oil burning normal for an engine with these many miles?
2. Are there any other tests I should have performed to confirm worn valve guides?
3. Would a leak down test confirm worn valves, or worn piston rings?
4. Are worn valves and/or rings common on these engines?



Thanks!

Zach L

1. Every engine burns a little oil and it's not uncommon for some oil to enter the cylinders when the engine is shut off while hot then sits overnight, but it should not be a lot of oil. 1 qt for 1,500 miles is more than typical.
2. A borescope can be used to inspect the cylinder walls for scoring
3. Yes, it will.
4. What you should be concerned about, and the most likely cause of your oil issues, is 'bore scoring'; not the valve train. Bore scoring is the more popular ailment suffered by these engines, particularly on the 3.4L in the 'S' models.

First, a typical rebuilt engine is LESS reliable and has more problems than a factory-assembled engine. I would not let your engine be 'rebuilt' by ANYONE that does not specialize in specifically these engines (i.e., M96/M97 Porsche engines). Check out Vision Motorsports in California, BGB Motorsports in Florida, Flat 6 Innovations in Georgia, or RND Engines for their engine exchange program.

About the bore scoring: It occurs because, in the quest for greater fuel mileage, Porsche used an inferior coating to line the cylinder walls that is supposed to be lower friction. What happens is the piston has enough tolerance to wobble a little when moving up and down the cylinder, causing scratches or boring on the cylinder walls. This occurs more often in the 3.4L engines because those engines have a longer stroke and part of the piston actually moves far enough downward that is passes the lower edge of the cylinder. Moving partially out of the cylinder allows slightly more 'wobble' that overtime can score the cylinder walls. Vision Motorsports will re-sleeve the engine using steel sleeves. Flat 6 Innovations will use their proprietary Nickies sleeves. I personally would lean toward the Nickies if I did a rebuild, but both are great engines and will solve your problems. If you go this route, I would throw in some form of IMS bearing solution while the engine is disassembled. The IMS has a failure rate of less than 1%, but your engine already has enough miles to warrant a service which can't be done without engine disassembly. More info on bore scoring: http://flat6innovations.com/cylinder-bore-scoring/

What bothers me is you have somehow been given the impression that a rebuild is "cheap". I would run from any place telling me that. More importantly, I highly doubt a valve train rebuild will fix your issues. With that many miles, the lower end is no doubt seeing some wear or will need attention soon enough. Furthermore, do yourself a favor and start working with someone that has an intimate knowledge of these particular engines. It may cost a bit more, but it'll be worth it. Don't throw your money down the drain in an attempt to save a few bucks. Do it once and do it right.

rpweimann

Someone beat me to it...and much more information then I would have posted.

PorscheAddict

Ditto what Zach said. More likely bore scoring than valve issues based on the frequency of issues on here. Borescope it. Rebuild is likely more than the car is worth at this point, unfortunately, at least from a reputable shop.

willie hernandez

Thanks Zach, rpweimann, and PorscheAddict, I really appreciate the info. I placed a call to Vision and had a great talk regarding the issues and possible solutions. It seem the concensus is to perform a borescope and leak down test. If those are good, then just put new cats and keep driving it because these engines use oil. If the tests are bad, my option is to spend $15,000 on an 11 year-old car.
I'll report back when the leak down and borescope are completed.

rpweimann

Do let us know what your findings are ... good luck.

willie hernandez

Thanks,
I've since spoken with Flat 6 Innovations, Rennsport (recommended by Flat 6), and Precision Motors.
I'm just trying to do my due diligence and absorb as much information as I can.
Here are the diverse responses I've received:
1. Perform a valve job and see what else the engine needs
2. Never perform a valve job
3. Put a new engine in
4. Leak down test first (X2)
5. Don't buy aftermarket cats
6. Buy aftermarket cats
I've tried to explain the issues consistently, but like medicine, it seems most mechanics are practicing their art with varied opinions as to what next to do.

rpweimann

Willie:

I think the boroscope and leak-down tests will be telling. Just like in the medical field, the doctor will order more tests until the issue is (hopefully) identified. We don't know the full story yet.

-Rob

rpweimann

By the way, I have a 2007 Boxster S, so I have a vested interest in your issue and the resolution of said issue.

PorscheAddict

Why would you replace the valves before even determining what the problem is? Borescope it, dude. If borescope shows messed up cylinder walls, you know what you need to do. If not, perform leakdown test. I can't imagine preventatively doing valves much less going ahead and buying a new motor.

willie hernandez

That's good to know because I was going to do a leak down test first. I'll have them do a borescope first because you're right, it would be the definitive way to figure out if I need to rebuild the engine.

Zach L

Willie, just want to say you've gone about this in the completely correct way... calling and talking to a bunch of different experts. I think you're on the right track and thank you VERY much for keeping us updated.

Your breakdown of options and advice already received in your conversations is really helpful and please let us know the findings of the borescope and possible leakdown tests. Hoping the best for you.

Pep!RRRR

willie hernandez

Thanks,
I have weighed this option. I'm torn between rebuilding this engine (if needed) and knowing what was wrong was fixed, or taking the chance of another engine having the same issues. I've also been eyeing trading in the Boxster for a BMW 335is. I loved the N54 engine's instant torque.

willie hernandez

Thanks. The rain's been keeping me in the truck, so the Porsche is in the garage. I need to find a reputable shop in So Cal to perform the tests.