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Q I have a 2006 Honda Accord four-cylinder with 105,000 miles. It has developed a clicking engine noise on a cold start. After the car has warmed up, the sound goes away. I have seen references to a condition called "piston slap." Is this something that I need to have checked out or to be concerned about?

A Is it piston slap, valve train noise or some other problem? Using a mechanic's stethoscope to locate the noise would pinpoint the source. Clicking or a sharp tapping from the valve cover on top of the engine would point to a valve train noise. A dull tapping or slapping sound from the side of the engine block would point more toward piston slap. Piston slap occurs on a cold engine when clearance between the piston's lower skirt and cylinder wall allow the piston to rock or cock slightly on the downward power stroke and slap against the cylinder wall, generating that slightly duller tapping sound.

Another possible cause is called CCDI, or combustion chamber deposit interference. This cold start noise is caused by a carbon buildup on the crown of the piston and roof of the combustion chamber, causing physical contact and a relatively sharp click at the very top of the piston travel.

Both noises tend to abate as the engine warms up. With piston slap, the aluminum piston skirt expands a bit as it heats up, eliminating the excess skirt-to-wall clearance. With CCDI, the clearance between the piston crown and chamber roof grows as the engine heats up, eliminating the contact. Decarbonizing the combustion chambers with SeaFoam or a professional induction cleaning would reduce or eliminate CCDI.

These types of noises are not catastrophic and typically don't mean a big engine problem is imminent. With 105,000 miles on the engine, I'd suggest just allowing a bit more warm-up before heading out on the road.

Honda recommends checking valve clearance at 110,000 miles. Wouldn't it be interesting if a relatively simple valve adjustment eliminated the clicking at start-up?

Q I have a six-cylinder 2005 Ford Escape with 180,000 miles. While driving on the freeway it started to lose power and smoke was coming from under the hood. I pulled over, and the engine died. There was a trail of oil and a pool under the truck. The oil filter and plug didn't seem to be leaking. I drained what was left of the oil and refilled it and installed a new oil plug. I again drove on the highway, and about four miles from home the same thing happened. The underside and back of the engine is covered with oil. The oil filter side is totally dry, but the other side is soaked. Head gasket maybe?

A Two distinct possibilities come to mind. With the loss of power at highway speed, the catalytic converter and/or exhaust system may be partially clogged or blocked, creating excess exhaust backpressure. This can overheat the exhaust and cylinder heads, causing excess oil consumption.

Perhaps more likely, the computer-operated electrical positive crankcase ventilation (PCV) valve is stuck closed or has failed. This would cause pressure to build up inside the engine and force oil out of seals and gaskets.

This scenario would take some driving to develop, which might explain why it occurs during freeway driving.

Q I have a 1998 Jeep Grand Cherokee. A few of the fins on the bottom of the radiator got damaged a bit, and it leaks. Does any product out there stop the leaks short of replacing the radiator? I had it replaced a year and a half ago and hate to buy another new radiator.

A I've had success with Silver Seal and Mendtite. But if there's physical damage, don't expect a stop-leak product to be a permanent repair. With that said, I see no reason not to give one a try.