What's the white crud on my spark plugs caused by?

Dear Car Talk

Dear Car Talk | Nov 01, 2004

Dear Tom and Ray:

My husband insists that the white crud that he finds deposited on the spark plugs of my 1998 Camry are the result of using any gasoline other than his favorite brand. I do use name-brand gasoline, but I tend to stop at the most convenient station, rather than go out of my way for his brand. Am I as irresponsible as he thinks? -- Sherrill

RAY: Tell your husband to get a life, Sherrill. That white crud shows up on spark plugs no matter what gasoline you use.

TOM: It's basically ash, sulfur and other unburned components from the gasoline that get deposited on the spark plugs over time. It can be made worse if you use a spark plug that's not hot enough, but I trust that your nit-picky husband has put the right plugs in your Camry.

RAY: But rest assured, that white crud is not doing any harm to your engine or your gas mileage. It's just that spark plugs DO burn down and corrode after a while, and they build up deposits. That's why manufacturers recommend that we do what? Change them every so often!

TOM: And think about this, Sherrill: The differences between brand-name gasolines are so small that the companies have to lure you to their stations by advertising the cleanliness of their restrooms. We think that's as good a reason as any for choosing one brand over another.

Get the Car Talk Newsletter

Got a question about your car?

Ask Someone Who Owns One