Miata Mailing List: May 1998, Message #7

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At 11:46 PM 4/30/98 +0000, Charles Lynch wrote:
>Gang,
>
>I've got a problem with my car. It is burning oil quite badly i.e.
>blue/black smoke out the back. If I let the car idle for a few minutes
>and then rev it up, I get a huge amount of Blue/black smoke.
>
>Other relevant facts
>
>1. Car has an indicated 115,00 Km (72,000 miles). The car is a used
>Japanese import so the milage may not be correct, although I believe it
>is.
>
>2. A Compression test gave very good figures (180-190) on all 4
>cylinders.
>
>3. It seems to have used 2 litres of oil in a month. I don't know what
>this is in U.S quarts/fl oz etc, but it's slightly more than half the
>oil you would put in for an oil change.
>
>4. Oil was Mazda's own 10W30 oil
>
>5. Spark plugs are fairly clean, although one is a little bit sooty.
>
>6. No oil leaks anywhere
>
>7. Fuel consumption seems to have improved, but then I'm driving it more
>gently :-(
>
>I think the problem is with the valve stem oil seals,
>Does anyone have any comments to make on this?
>
>Bill, Lester, Anyone?
>
>Thanks in advance
>
>Charles Lynch
>91 Silver
>Auckland,
>New Zealand
>AKA - Land of the long white cloud :- mainly from Steve Hung's car? ;-) 
>
Hmm, if it's not leaking it, it's either going down the intake guides or
past the rings. Compression test tells you nothing about oil ring condition
unfortunately, nor will leakdown test. Haven't seen valve seals failing on
them, though if roasted nicely (as in major overheat), they could certainly
get crispy. About all you can do is pull the cams and lifters, hold the
valves up with compressed air and pull the springs to have a look at the
seals and guides. If you don't find the problem there, it's time for rings.
Hate to say it, but I would vote for rings...Let us know what you find,
enquiring minds want to know. Good luck!

PS Before anyone asks why I mentioned only intake guides...there's no
vacuum in the exhaust ports, so exhaust guides have to be *really* bad
before they will pass much oil. Lots of racers leave the seals off the
exhaust side. FWIW
bill cardell
Dealer Alternative, Inc.
"We make Miatas fly!"
970-464-0878
http://www.dlralt.com