My van is about to hit 60K miles, and it appears the spark plugs and wires need to be replaced. As many know the front 3 are easy, and the back 3 are hard. I have just replaced the front 3 plugs and wires. If I leave it this way for a few days, is it possible for the 3 olders ones, to stress or damage the 3 newer ones, or all 6 pretty independent of each other?

 

I don't think it will hurt the engine the one thing that it would affect is fuel economy as the new new plugs burn better than the old plugs causing uneven burning but probably nothing you would notice when I worked at a garage I changed a lot plugs incars that the owner at one time replace the front plugs but never changed the rear ones and now they were so worn out they would barely fire so they brought it into us to chabge them all

 

I have to agree the only thing that it will hurt is the fuel milage but I would change them at some point it might give you codes from the O2 (oxygen sensor) depending on if it has one for the front and rear, thay will read more gas burning in the front and less in the back causing added air might also studder or miss!