Occasional puffs of oil smoke from tailpipe

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my_two_cent - 03 Dec 2006 00:25 GMT

I'm getting occasional puffs of bluish smoke from the tailpipe of my 96
Miata 1.8L.

I replaced the PCV valve, which I know can cause smoking if it fails. I
also put clamps on both ends of the hose that connects the PCV value to
the intake manifold and I replaced the grommet that the PCV valve goes
into in the valve cover. I also taped the end of the hose that connects
the other side of the valve cover to the air intake just in front of
the throttle plate. I think I have all possible air leaks fixed for
these parts.

All of these repairs fixed the problem to some extent, but still, on
occasion, when accelerating away from an intersection, particularly
when turning, I get pinging and a quick puff of blue smoke, sometimes
hard to see, sometimes a big fat cloud.

Any ideas on what else I can check before taking it to a service
garage? Is there anything in the idle air components that could cause
this?

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Lanny Chambers - 03 Dec 2006 04:41 GMT

> All of these repairs fixed the problem to some extent, but still, on
> occasion, when accelerating away from an intersection, particularly
> when turning, I get pinging and a quick puff of blue smoke, sometimes
> hard to see, sometimes a big fat cloud.

Need more info:
How many miles on the engine?
What's the farthest you've driven without changing the oil?
What was the most oil you've ever added between changes?
Has the car ever overheated?
Where do you live?

Signature

Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

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my_two_cent - 03 Dec 2006 22:23 GMT

> Need more info:
> How many miles on the engine?
> What's the farthest you've driven without changing the oil?
> What was the most oil you've ever added between changes?
> Has the car ever overheated?
> Where do you live?

120K miles
no more than 5k miles between oil/filter changes, usually 3-4 k
I use Castrol or Quaker State 10W-30 and Fram oil filters
I only occasionally get the valve noise when the engine is cold
I seldom add more than a pint of oil between changes
A long time ago, I lost a heater hose and the radiator ran dry, but the
engine didn't really overheat.
I live in San Diego county where it never freezes and nobody
deliberately throws salt on the roads.

I can see where you are going with this. I don't get any smoke under
any hard acceleration conditions, except after coming to a stop at an
intersection, and then only very briefly. Could it possibly be piston
rings? I don't have a compression tester, but if it's possible, I am
willing to buy one and test the compression if that is what you advise.
But I expected if it was piston rings, the onset wouldn't be so sudden
and the effect would be more constant, less erratic than I am
experiencing.

Could it be a head gasket leak? How could I diagnose this?

Thanks for your help.

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pws - 03 Dec 2006 23:15 GMT

> 120K miles
> no more than 5k miles between oil/filter changes, usually 3-4 k
[quoted text clipped - 18 lines]
>
> Thanks for your help.

You are probably looking at a bit of seepage at the rings, not unusual
for a 120K mile car. I would avoid Fram filters, they may be fine but I
go ahead and use the factory filter or a Wix every time.

Doubtful on the head gasket, that is a problem that usually grows quickly.

Lanny says that his car loses literally no oil between changes at
140,000+ miles. I am not doubting him, but I don't think that this is
typical.
Nearly every car I have ever serviced, which is quite a few, has started
using at least a little oil by 100,000 miles, whether they had good
maintenance histories or not.

Pat

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Lanny Chambers - 03 Dec 2006 23:23 GMT

> I can see where you are going with this.

Yeah, it's worth trying to eliminate the usual suspects. Good
maintenance habits are important, but can be undone by a single lapse.

> I don't get any smoke under
> any hard acceleration conditions, except after coming to a stop at an
> intersection, and then only very briefly. Could it possibly be piston
> rings?

Sounds more like valve stem seals.

> But I expected if it was piston rings, the onset wouldn't be so sudden
> and the effect would be more constant, less erratic than I am
> experiencing.

Bad rings get worse gradually. You generally don't start noticing clouds
of blue smoke in the mirror until you're using a quart every 500 miles.
People following you will see (and smell) your oil at a much earlier
stage.

There's a large, active Miata club in San Diego, ready to offer
diagnostic help, advice, and recommendations for repair shops, if it
comes to that.

Signature

Lanny Chambers
'94C, St. Louis
http://www.hummingbirds.net/alignment.html

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pws - 03 Dec 2006 23:28 GMT

> Bad rings get worse gradually. You generally don't start noticing clouds
> of blue smoke in the mirror until you're using a quart every 500 miles.
> People following you will see (and smell) your oil at a much earlier
> stage.

I saw one of my old 280Z's on the road yesterday! It was putting out the
same color of smoke that it was when I owned it, laughing at the
emission laws since it was made in 1976.
That thing was using about equal parts of gas and oil when I dumped it
about 12 years ago. (slight exaggeration)

Pat

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my_two_cent - 24 Dec 2006 01:16 GMT

I changed the oil to a 10W40 from a 10W30 and it helped the valve
clatter a bit, but not the smoke, so I ordered an OEM PCV valve from
GoMiata and replaced it and -- no more smoke.

So that is one original OEM PCV valve with no problems and three
non-OEM replacement PCV valves with more or less serious performance
problems. I'm sticking with OEM PCV valves from now on and a strict
replacement regimen.

I want to thank everyone who answered my question, esp. Lanny who
somehow always answers everybody's questions. I think this is the third
or fourth difficult question in the life of my '96 M edition that Lanny
has helped me with over the years, from tires/wheels and shocks to top
replacement and now smoking.

This is what Usenet is all about, and has been for twenty years. I'm so
glad that while so much else of the original Internet community has
disappeared, Usenet community has not.

Thanks again to all.

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