Occasional puffs of oil smoke from tailpipe

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.

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

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

Sounds more like valve stem seals.

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.

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

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.