My engine uses about a quart of oil every 1,000 miles. Should I be concerned?
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.