Q: I have a 2005 Mazda 6 with the 3-liter V6 engine and 70,000 miles. I do my own oil changes and for the past several changes have noticed a strong smell of burning oil when stopped at lights or in traffic, lasting three weeks after I have done the oil change. I am very careful not to spill any oil onto the exhaust when removing the filter, and to eliminate this possibility I left the filter in place after the last change. This failed to eliminate the problem. The engine burns no oil between changes and no smoke is visible from the exhaust. Any help would be greatly appreciated.
A: In most cases, smelling hot oil at idle indicates some type of external leak or spillage that drips onto the hot exhaust. In addition to the exhaust components near or under the oil filter, check to make sure no oil is dripping from the valve cover gaskets onto the exhaust manifolds, particularly from the front valve cover with the oil filler cap. Perhaps enough oil collects against the gasket when you refill the engine with fresh oil that it slowly migrates past the gasket and drips on the manifold.
The other system to focus on is the positive crankcase ventilation (PCV) system. Your engine features a PCV valve plumbed into the induction system downstream of the throttle plate, meaning engine vacuum pulls crankcase vapors into the combustion chambers where they are burned. If the PCV valve is stuck or clogged and doesn’t open under engine vacuum, the crankcase may become somewhat pressurized and force oil and vapors past the piston rings and into the combustion chambers.
Q: I have an ’83 Jeep CJ-7 with the 258 six-cylinder engine. The oil pressure gauge was showing about 50 pounds per square inch when it suddenly went to zero. I connected a mechanical gauge to the engine block and it showed 60 psi. Is this an easy fix? How does the electrical gauge work?
A: Could you mount the mechanical gauge in or under the dash? If so, you’ve “fixed” your problem. I’ve always preferred mechanical gauges anyway for two reasons — they are instant and accurate, and not subject to electrical gremlins.
To determine whether the problem is the gauge or the electrical sending unit on the engine, disconnect the wire from the sending unit and connect a 12-volt test light from this wire to ground. Turn on the ignition. If the lamp flashes, the instrument voltage regulator is good. If the lamp stays lit, the regulator is bad. If the lamp doesn’t light, check the regulator’s connections and ground. And check for an open circuit in the connection from the regulator to the gauge.
And finally, if the lamp flashes as it should but the gauge isn’t accurate, the gauge is the likely culprit.