Why your car's engine might be knocking (Hint: it's not the oil)

I drive a 2009 Honda Pilot Touring 4WD. I hear some knocking when I start the engine. It eventually becomes relatively quiet after a minute or two. Would it be a good idea to start using synthetic oil? -- Ross

When you hear a knock, knock in your engine -- synthetic oil probably isn't the answer, experts say.

"There are a number of possible causes of knocking or pinging sounds in vehicle engines," says Hayato Mori, product planning manager at Honda Canada. "I can say that switching to synthetic oil is unlikely to be your answer -- the Honda Pilot does not require synthetic oil."

Generally, when the engine is making strange sounds, the aptly-named engine knock is often the culprit. When the engine is working properly, the spark plugs ignite the gasoline in perfectly-timed waves that move the pistons.

If the gasoline ignites on its own before the spark plug fires, because of engine pressure or engine heat, it explodes, making a knocking or pinging sound.

"Sometimes knocking sounds can be caused by using the wrong type of fuel for a particular vehicle, for instance, using regular unleaded if a vehicle requires higher octane fuel," Mori says. "Other times the sounds could be caused by a malfunction with the spark point. Issues that fall into this category include spark plugs that need to be replaced, ignition timing issues or any number of other possibilities"

The gasoline's octane rating reflects how quickly it will ignite. If an engine is designed for premium (91), using a cheaper, lower-rated gas might cause knocking. Generally, experts say to try a lower octane gas in vehicles calling for premium (as long as higher octane is recommended but not required) and switching back if knocking occurs.

But the Pilot's manual says it's designed to operate on "unleaded gasoline with a pump octane number of 87 or higher." That's regular. It does suggest switching to premium when towing.

Mori suggests your Pilot's knocking could be caused by "spark plugs that need to be replaced, ignition timing issues or any number of other possibilities."

But again, the type of motor oil you use probably isn't one of them, says Jay Kavanagh , engineering editor at Edmunds.com.

"Type of oil has nothing to do with traditional engine knock (a.k.a. detonation, pinging) one way or the other," says Kavanagh.

Nevertheless, there are tales on the Internet from folks who say switching to synthetic oil solved their engine knock -- others say the switch to synthetic caused their cars to start knocking.

Kavanagh says the only oil-related problem that might ever cause the sound in an engine is a lack of oil.

"By then, the type of oil, synthetic or conventional, is already a moot point," he says.

Readers, if you've experienced a similar sound when starting your car (whether or not you got that knock to knock it off) -- join the conversation.

Send your automotive maintenance and repair questions to globedrive@globeandmail.com