On a four-cylinder engine, cylinders two and three have lower compression than cylinders one and four. The spark plugs in cylinders have white chalky deposits on the insulator and electrodes. What is the most likely cause?
Damaged air filter element
Damaged head gasket
PCV valve stuck open
Intake manifold leak
The answer is 2. If you chose 1, this is rare and would cause round glass-like beads to form on the spark plug. It would have also affected cylinders one and four. 3? Well, a stuck PCV valve will cause black deposits. Did you choose 4? A leaking intake manifold can cause the engine management richer or leaner, but the deposits would be black.
A coolant leak is the most likely cause. Internal coolant leaks can foul a spark plug and cause a misfire. The problem could be a leaking intake manifold or a head gasket, and the fouled plug might be localized to one or two adjacent cylinders. The burned coolant leaves deposits on the electrodes and insulator, creating hot spots that could cause pre-ignition and a misfire code being set. When the plug is pulled, it might have a chalky appearance on the ground strap and center electrode. Modern coolants do not cause this type of buildup quickly due to the reduction of phosphate, zinc and other additives that can contaminate the catalytic converters. Unfortunately, it also means that drivers will run a vehicle with a coolant leak for several thousand miles while the plug becomes slowly fouled. In the past, the converter would become clogged and stop the engine before significant damage was caused.
After an engine oil and filter service, a technician can’t get the oil pressure warning light to go out after 10 seconds of running and is not in the correct range. What is the MOST likely cause?
The oil filter
Wrong viscosity oil installed
All the oil has run out of the pump
Air trapped in the pressure sensor
The answer is 3. Although not a common occurrence, it is very possible that the oil pump may lose its prime during the oil change. When the used motor oil is drained from the engine the oil may also drain from the oil pump pickup tube and possibly from the oil pump itself. When new motor oil is installed the pump’s pickup tube inlet again becomes submerged, trapping air in the tube on the suction side of the oil pump. Sometimes this problem can be avoided by limiting the time the oil is drained. The trapped air will cause cavitation of the pump and prevent it from producing oil flow and pressure. Many techs tend to blame this on the oil filter and assume that the filter is blocking the flow of oil. The point being made is the oil filter was not the problem and in most cases there is a simple solution. If after the oil and filter change, the red light or low oil pressure remains for ten seconds, shut the engine off, remove the oil filter and, using an oil squirt can with the correct motor oil, squirt oil several times into the oil filter base outlet on the engine. Next, fill the filter with new motor oil and reinstall. Start the engine and check for oil pressure. In most cases, the problem will be solved. DO NOT allow the engine to run for more than ten seconds without oil pressure. Use a watch to time the ten seconds and be sure of the elapsed time. In some instances, the full ten seconds is needed for the pump to recover oil flow. If this fails, again remove the filter and crank the engine until oil spills from the engine base. DO NOT crank over ten seconds at a time. When oil spills, reinstall the oil filter, correct the oil level and restart the engine. Oil pressure should now be back to normal.