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hey i just checked my spark plugs.....the insulation on the inside of the plugs around the lower terminal was brown and chalky.......the car was overheating due to a head gasket failure so they may be the same plugs from then ......would this effect my mpg?.....the terminals seemed fine

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hey the deposits were mediocre but it was the melted middle point that got me....i looked at new plugs and the bottom terminal there is a point that goes up from it but the plugs i pulled out didnt have them....plus they had a .046-.048 gap when its supposed to be .044"....so i replaced them

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If you have a haynes manual (for any vehicle) available, check out like inside the back cover. All the haynes manuals I've had anyway had a full color glossy page showing like 16 different spark plug issues and the possible causes.

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Im confused. Were they new plugs? Because that can blow a HG. And yes, I do believe that having the wrong plugs can affect your mileage. You should have NGKs or if you have to Densos.

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