Question: My engine uses about a quart of oil every
1,000 miles. Should I be concerned?
Answer: Not if you plan to sell or trade your vehicle
soon. An engine that uses a quart of oil every 1,000 miles is
starting to show the effects of wear. The amount of oil it is
using is still acceptable, but it will gradually increase as the
miles add up. When it reaches the point where it's using a quart
every 500 miles or less, it's time for an overhaul.
Oil consumption depends primarily on two things: the valve
guides and piston rings. If the valve guides are worn, or if
there's too much clearance between the valve stems and guides,
or if the valve guide seals are worn, cracked, missing, broken
or improperly installed, the engine will suck oil down the guides
and into the cylinders. The engine may still have good compression,
but will use a lot of oil.
An oil consumption problem caused by worn valve guides can
usually be cured by a valve job. Knurling, sleeving or replacing
the guides, or boring out the guides and installing valves with
oversized stems will stop the loss of oil.
Oil can also get past the rings if the rings or cylinders
are badly worn or damaged, if the cylinders were not honed properly
when the engine was built (or rebuilt), or if the rings were installed
improperly.
When a newly-built engine is first started, the rings require
a certain amount of time to "seat" or break-in. If
the rings fail to seat properly, the engine will use oil. This
may be the case if somebody applied the wrong finish to the cylinders,
failed to clean and lubricate the cylinders properly before the
engine was fired up, or didn't use the proper break-in procedure.
If the rings and/or cylinders are at fault, the engine will
have lower than normal compression readings.
In some instances, worn rod bearings, excessive bearing clearances
and/or excessive oil pressure can splash too much oil on the cylinders
causing oil to get past the rings.
The cure for worn rings and cylinders is to overhaul the engine
block. The cylinders have to be refinished and new rings installed
to regain good oil control.
