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Old 11-11-2012, 02:54 PM   #1
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Default Oh noes! Thin film of oil on plugs.

I pulled my MP62 off to permanently sell it this winter. Having prepped everything for higher boost, save the engine, intuition tells me that taking a step back to naturally aspirated on this engine is the correct decision.

While swapping the spark plugs back to OE, I found every plug had a thin film of oil around the threads and washers. So, I did a compression test and compared numbers to last year.

May 2011
Dry Wet
166 185
168 180
152 175
150 175

Nov 2012
Dry Wet
160 169
151 151
149 160
143 159

I've attached a few pictures of the cylinders after the wet comp test. They sure look like something crispy, no? How quickly do I need to start researching parts for an engine build thread?
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Oh noes! Thin film of oil on plugs.-img_0002.jpg   Oh noes! Thin film of oil on plugs.-img_0003.jpg   Oh noes! Thin film of oil on plugs.-img_0004.jpg   Oh noes! Thin film of oil on plugs.-img_0005.jpg  
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Old 11-11-2012, 06:54 PM   #2
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sure its not oil that has leaked down from the cam cover gasket and then onto plugs and into cylinders when you removed the plugs?

does not explain the difference/drop in compression but if the oil is as bad as you say i would have thought there would be other signs... like smoke...
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Old 11-11-2012, 10:09 PM   #3
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Oil is from the cam cover gasket as ms2daj says. Wouldn't worry about it. Looks like carbon buildup on pistons. Wouldn't worry about that either. Your compression numbers could be chalked up to the gauge. Are you noticing performance issues?
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Old 11-11-2012, 10:19 PM   #4
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No performance issues that I can quantify. I've run the compression numbers a few times over the past few years, using the same gauge, and they have been consistent enough to show show wear and tear. The MP62 ran almost identical numbers as advertised when it was dynoed last year.

The last two sets of plugs read perfect in terms of color.

Looking back at my records, it looks like I may have changed the CAS o-ring immediately after getting the car in 2009. I do not have any record or remembrance of changing the valve cover gasket.

Your responses put me a little more at ease.
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Old 11-12-2012, 01:40 AM   #5
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I see no problems here.

As others have said, that oil leakage is pretty typical for the Miata. And the carbon buildup on the pistons is pretty normal for any car this age.

I wouldn't fret the compression numbers, either. Hell, they're better than the engine in my '90, and I have absolutely no plans to replace it any time soon.
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Old 11-12-2012, 10:07 AM   #6
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That's more good news. Thanks for the input.

I'll look at changing the valve cover gasket before it gets too cold out.
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Old 11-12-2012, 10:40 AM   #7
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You might try the Sea Foam or B12 through the vacuum port. Will help with the carbon buildup on the piston tops, valves and intake manifold. Marvel Mystery Oil will also help break that gunk up and can help if you have gunky rings which could lower your numbers too.
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Old 11-12-2012, 11:58 AM   #8
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Valve cover gasket!
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Old 11-12-2012, 01:43 PM   #9
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You're fine.

Congrats. Your motor intelligently lowered its compression ratio to accommodate more boost.

Also that is just carbon on the pistons. Normal
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Old 11-12-2012, 02:53 PM   #10
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You know, I remember trying the "Seaform Trick" several years ago on my '92, just before I installed the turbo on it. Aside from putting out a cloud of smoke that enveloped the entire neighborhood (fortunately, I did this in an empty office park on a weekend), it didn't seem to actually accomplish much. I had the head off about a year later to replace the gasket, and the piston tops looked ever bit as foul as the ones in the picture above. So I scrubbed 'em for a while with a toothbrush and brake cleaner. That did the trick.
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Old 11-12-2012, 11:33 PM   #11
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I ran Seafoam through shortly after I bought the car and didn't notice enough of a difference to use it again. Oddly enough, I was running water injection the last few months, and the pistons still look like this!
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Old 11-13-2012, 12:21 AM   #12
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Water injection won't remove the stuff that is already caked on there. A wire wheel will. Or a chisel, etc. I ran WI for quite a while and when I tore down the old motor it looked just as nasty as yours. I am also unconvinced of SeaFoam's effectiveness, other than killing any insects and small children near the car when you run it through.
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Old 11-13-2012, 12:33 AM   #13
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I've been a supporter of Seafoam. It's effectiveness is limited, though. I've used it on past cars where I let it sit overnight after choking the engine off with it, and the engine idled notably better after blowing everything out the next morning.

When I ran it on this car, I only ran it while idling. It cleared a thin path from the vacuum port to the cylinders, but that was about it.
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Old 11-13-2012, 04:48 AM   #14
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run more water :b
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