have a 2003 Pontiac Vibe with 135,000 miles on it. This past winter
it would knock for a minute or so on a cold start. A GM tech told me
that it has a cold piston slap and it will go for a long time. Now I
can faintly hear it this summer. Could it be anything else? Is there
something I need to do so it will last two to three more years and
to get close to 200,000 miles out of this or any engine is a worthy
goal, but of course there are no guarantees, knock or no knock. The
GM tech is likely correct. Piston "slap" occurs when the
excess clearance between the piston skirt and the cylinder wall
allows the skirt to "slap" the wall as combustion pressure
drives it downward in the cylinder. As the piston warms up and
expands a bit, the clearance is reduced and the noise stops. And as
the tech said, this isnít particularly harmful and does not mean
impending failure. The engine in my í70 Corvette with 120,000
miles on it has reminded me it has a slight piston slap every time I
have started it for the past 20 years.
stethoscope can pinpoint the particular piston/cylinder in question.
If disabling the spark for that cylinder during a cold start test,
which eliminates combustion pressure that slaps the piston skirt
against the cylinder wall, eliminates the knock, itís piston slap.
If it is
piston slap, donít worry about the noise and just drive the car.
The only "repair" would be a complete engine overhaul,
which would not be economically justifiable.
more possibility: combustion chamber deposit interference, or CCDI.
This occurs when carbon deposits build up on the top of a piston
and/or the roof of the combustion chamber to the point where there
is physical contact between the two on cold starts until all the
components warm up and expand enough to eliminate the contact.
Again, like piston slap, this isnít particularly harmful, but
unlike piston slap, it may be easily "fixable."
or DIY induction cleaning with SeaFoam or GM Top Engine Cleaner can
remove the carbon build-up and eliminate the noise.
Q: I would
like to better understand oil change intervals on little used
vehicles. I have a í77 F-150 that I use around the ranch about 20
hours and maybe five miles per year. I completely rebuilt the
engine, and the oil I put in more than five years ago is still
honey-colored. Am I hurting the engine? Seems silly to change it
every year, but is there a shelf life?
A: In this
case, the word "silly" is synonymous with
"wasteful." I just checked the date I last changed the oil
and filter on the aforementioned íVette and it was 2009 ó four
years ago. In that time Iíve driven the car less than 2,000 miles,
so I guess youíve reminded me itís time to change it again.
But I have no
worries that Iím hurting this engine, or any other "low
annual time/mileage" engines I own and operate. The oil in
these engines is subject to very little fuel/combustion blow-by
contamination. The only time-based deterioration is oxidation from
exposure to air inside the engine.
I think youíre
safe, but itís probably time for an oil and filter change. Save
the old oil for recycling or use in topping up oil levels on your
other low-annual-time engines.