[Vwdiesel] Compression and Leak-Down Test Results

[Gavrik Peterson]

I just did some work on that 1.6 liter diesel engine with the leaking
head gasket.  First I did a compression test:

 Cyl#     (PSI)
  1        540
  2        524
  3        595
  4        583

The interesting thing is the pressures are all above the 483 PSI spec.
for a new engine.  When I removed the head, the top of the piston and
the head were covered with a thin layer of carbon.  Could such a small
amount of carbon cause such a high compression test pressure?  Is it
common to have pressures higher than 483 PSI?

I then used my leak-down tester.  I pressurized each cylinder to 80
PSI and then observed the difference in pressure across the orifice.

 Cyl#  (Delta PSI)
  1         4
  2         3
  3        10
  4         4

This leak-down tester has a pressure regulator which allows you to
control the cylinder pressure.  When I performed this test ten years
ago, I would slowly raise the cylinder pressure.  First you would hear
increasing leaking noise that sounded like it was coming from the
rings.  Then when the pressure would reach something like 20 PSI a
compression ring would seat and the noise and leak rate would go way
down.  Then I would adjust the pressure to 80 PSI and take a reading.

In the test I just did, the leak rate was higher (I think) and I was
not able to observe the rings seating on 3 of the 4 cylinders.  On the
one that seated (#2) the effect on leakage and noise was slight.  This
is quite different from the way they seated ten years ago.  At that
time they seated at the same pressure and the seating action was crisp
and obvious.

While I did the leak-down test, I allowed the cylinder pressure on
each cylinder to remain high for around ten minutes and then checked
to see if there was any leakage pumping up the coolant system
pressure.  This showed that cylinder #2 had a leak to the coolant
system.


  --  Gavrik