Okay so I changed my engine oil almost three months ago, I used Royal Purple 10w-30. I also changed the spark plugs and put in some copper Autolite 605s. I have only put 820 miles on my car since then. So my question is, how longer should I wait until I change both the spark plugs and the engine oil?

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98' Grand Prix GTP Sedan

When you get to 4000 miles on the oil...............and when the plugs need it...........which could be a long time. I often do not change plugs for years if I am tuned properly or on a stock car (not stock). Oil today is so much better then years gone by even conventional oil(as well as gas). The additives that are used prevent it from deteriorating like it used to. (IE car sat from OCT to now. Last week I removed the gas from car----cuz changing to e85----and put it in my truck. It ran fine and I did not put any additives in the fuel tank last year.)

That being said, oil is way more stable then fuel. I would not change it until 4000 miles imo. Or 3000 if you choose, but that is unnecassary today too.

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01 GTP SE Sold. 89 Mustang Vert 331 T-trim