Great Blue Clouds - Likely culprit?

[Purrybonker]

So, my 3.2 has been running like a charm until I swapped out the cat for one of those wonderful Dansk pre-mufflers (thanks PP). After the conversion the car is now (inconsistently) producing blue smoke, particularily at idle. Sometimes lots of it, poor pedestrians holding their noses. Increasing RPM - revving the car up will usually seem to clear up the smoke problem - at least until the next red light.

What's really strange is the inconsistency of the smoke problem - but it is definitely more prevalent when the engine is even slightly below operating temp. As an example, I had it idling hot in my garage for 20 minutes or so while I checked/added oil - no smoke or even noticeable smell. But at the first set of lights after leaving my garage it pumped out a few blue clouds.

The car leaks none, but goes through around normal amounts of oil (qt/750miles or so). With the cat in place, smoke was previously visible only briefly at start-up.

My mechanic suggests that there is a ring and/or seat problem and that the cat has been hiding the burning oil evidence. We're going to look into the matter further next week.

This is all very concerning, of course. Can the cat conceal oil burning habits of an engine and what is the likely culprit (rings/seats or other) with these symptoms?

The car is an '87 with about 80 thousand miles.

[Purrybonker]

Don't laugh, but it just hit me...

I did add a quart or so of oil just before I started having this smoke problem. But I religiously checked both the guage and the dip-stick for level. It was just over the bottom line, if I recall correctly.

Now I can't wait to get home and check the air intake for oil residue - I should be so lucky...

I'll have to banish myself from this board for a while if it does turn out that I overfilled it!

[Jim Sims]

"But I religiously checked both the guage and the dip-stick for level. It was just over the bottom line, if I recall correctly."

But was the engine at operating temperature, idling with the car on level ground when you checked the oil?

If you overfilled don't worry about it; just clean up the mess and drain some oil out. Many have overfilled in the past and many will do it in the future. Cheers, Jim

[Wayne 962]

Also, check to make sure that your O2 sensor is still plugged in correctly - it may have come loose or not been connected correctly when you reconnected everything...

-Wayne

[Purrybonker]

No such luck with the oil level - intake is clean, O2 sensor hook-up looks to be good. This has really got me boggled - this is how crazy this is:

Let it idle for about 45 minutes today - clean on start-up, no smoke at all on initial crank. After about 10 minutes or so of clean air it started to push some blue. Rev it up - cleans up nicely. Back to clean idle again. This cycle pretty much repeated for the whole 45 minutes - the blue would even clear without reving if left to it's own devices.

All of this with the oil tank vent line to the intake disconnected. Car idles and run smoothly with good power.

No noticeable change in smoke production after a moderate drive - same sort of on again-off again mild blue smoke cycle. At least I was unable to reproduce those neighbor offending blue clouds from the other day.

I guess I'll have to pull some plugs to look for insight before digging further. Recent compression had all 6 in a very tight grouping around 160 (we're around 3500 feet here - even more on a good day).

Any other suggestions as to what could cause intermitent smoke in this manner?

BTW- would a misconnect with the O2 possibly result in blue or black smoke?

[Nathan M]

My car had exactly the same symptoms. Great compression, great performance, just intermittent (big) blue clouds. Pulled the valve covers off and found worrying amounts of side to side play on the exhaust valves. Put it back together, ran it for the remainder of the summer (embarassing at times), and I'm now in the process of tearing it down for a top-end job. BTW, my car's done 78000 miles.

[Wayne 962]

Run:

- Compression test
- Leakdown test
- Mixture measurement / test

and let us know what you find...

-Wayne

[Purrybonker]

Question asked and answered.

Plenty of wiggle in those valves.

Time to get out that other book of Wayne's and read up. Then I'll be in a better position to understand where all of that cash draining out of my bank account is going to.

[cstreit]

How's your oil pressure? Since it starts at idle, makes me wonder if there's oil backing up and filling up the sump.

Oops... Just saw your last post...

[toolman]

HI Purr, I had the same thing happen when I changed the exhaust. I think the cat somehow cleans up some of the oil smoke. I have 77,000 on my 87 Carrera and have the engine just about put back together after a top end rebuild. My exhaust valve guides were really bad and had leaked oil into the exhaust ports depositing a thick layer of carbon. I had the heads redone and installed new pistons and cylinders for good measure. I will be installing it in about 2 weeks and will let you know how it worked out. So far the cost has been about $3900.

[Purrybonker]

Thanks for the comments - even misery loves company.

Yeah, I was really wondering about that cat hiding the smoke thing, nice to know that someone else has witnessed this as well.

What P's & C's did you go with?

I'm leaning toward 3.4's - the euros probably don't make sense with fuel options here.

[toolman]

I went with the stock 9.3 to1 ratio since I got a smokin' deal from MS Roadrace. $1500 for the new ones and sold the old cylinders for $375 to a guy that was boring them out to 98mm for a 3.4 litre. I wanted to go with the 3.4 setup with 9.8 to 1 compression but that would have cost about $2400. I researched the euro option and I could have done it no problem since 93 and 94 octane is readily available. Next is a Steve Wong chip to replace the Weltmeister.