understanding smoke...

klassiek911 · 08-30-2006, 11:58 AM

I'm new here but not first to ask about tailpipe smoke (my 2.4S is suffering from it ). I've read some old threads to try to understand how to read the problem. They talk about how smoke in deceleration vs idling vs pulling away scenarios mean different things, but I am piecing bits together and not getting full picture. Could someone clarify what driving tests I can do to understand better what the likely problem is with my car and whether I am looking at top-end or full rebuild? What exactly is meant by smoke at deceleration? And does this indicate valve guide rather than piston ring wear?

Gasman59 · Gasman59's Garage

Basically with your throttle closed and the car braking via the engine, you build up vacuum in the intake system which pulls oil past the worn valve guides/seals.
Hit the throttle after some time and there will be a telltale puff of smoke as the oil burns off.
I have a 1/2 mile hill near me which is ideal for this test.
Ron

Steve@Rennsport · 08-30-2006, 04:03 PM

Quote:

Originally posted by Gasman59
Basically with your throttle closed and the car braking via the engine, you build up vacuum in the intake system which pulls oil past the worn valve guides/seals.
Ron

Worn rings will do the same things as high cylinder vacuum pulls oil past the oil control rings.

The best thing to do is have a leakdown test performed to pinpoint the source of any compression loss. This will help pinpoint the source of oil consumption.

klassiek911 · 09:07 AM

Quote:

Originally posted by Steve@Rennsport
Worn rings will do the same things as high cylinder vacuum pulls oil past the oil control rings.

The best thing to do is have a leakdown test performed to pinpoint the source of any compression loss. This will help pinpoint the source of oil consumption.

I had compression test done last year, all cylinders were 10bar (not sure what that is in psi but they were all the same value which is the important thing right).
I had a leakdown test done this year, which was far worse:
7%, 12%, 24, 26, 28 and 30%.
But I only started really noticing the tailpipe smoke appear after I had 2 new valve covers installed (both sides leaked).

Is it possible to get such different results from compression vs leakdown test?
Could valve cover replacement have anything to do with it?

Oh and this: the car had only done about 4000 miles in 10 years when I bought it last year. Since it has done about 1500 miles. And when I got it it was running way too rich (black smoke on hard acceleration). That's all the facts.

Steve@Rennsport · 08-31-2006, 05:23 PM

Quote:

Originally posted by klassiek911
I had compression test done last year, all cylinders were 10bar (not sure what that is in psi but they were all the same value which is the important thing right).
I had a leakdown test done this year, which was far worse:
7%, 12%, 24, 26, 28 and 30%.
But I only started really noticing the tailpipe smoke appear after I had 2 new valve covers installed (both sides leaked).

When they performed the leakdown test, did they observe and note WHERE the leakage came from? Intake ? Exhaust? or Oil tank?

klassiek911 · 09-04-2006, 10:53 AM

Quote:

Originally posted by Steve@Rennsport
When they performed the leakdown test, did they observe and note WHERE the leakage came from? Intake ? Exhaust? or Oil tank?

I'll ask them. Thanks for the advice.
Would it just be an odd coincidence that the problem manifested itself after fixing the valve covers?