Niagara Gazette

Features

October 4, 2013

TOM'S CORNER: Touching on oil consumption and other questions

Niagara Gazette — SPENCER FROM AUSTRALIA: I own a 2008 Ford Mustang with 91,000 miles. At about 85,000 miles it started burning oil (no leaks obvious) with blue smoke in the exhaust on startup. In the last couple of months the oil consumption is rapidly increasing. On “general principles” I replaced the PCV valve recently to no avail. On a bulletin board for these cars, there has been talk of valve oil seal problems. Could the seals get to the point where they fail completely and oil consumption take a sudden leap?

TOM: Yes, seals could harden and break up, causing oil consumption to accelerate greatly as oil spills down the valve stems and into the combustion chambers to be burned. Pull a valve cover and inspect the valve seals. If the valve seals are intact and ok, then it’s time to delve deeper into engine diagnostics with a cylinder leak-down and compression test.

Good luck, mate! (I wonder, do you knows the Geico lizard?)

Spencer asks a question that many vehicles experience, namely oil consumption at high mileage. What are the causes? What diagnostic tests should be performed?

 

CAUSES OF OIL CONSUMPTION

• Bad valve seals: The valves are located in the cylinder head above the combustion chamber. Oil is pumped at 50 to 80 psi of pressure into the top of the head, lubricating the valve-train. The valves have seals that stop the flow of oil down into the engine when the valve is open. If the seals fail, oil flows down into the combustion chamber and is burned.

• Worn valve guides: The valves are guided by a small cylindrical chamber called a valve guide. These guides wear over time causing eccentricity (slop). The excess gap allows oil to flow down the valve stem and into the combustion chamber to be burned. You might be wondering why the valve seals don’t stop the oil. It’s because the gap is too large for the seal to work.

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