Spark Plug Advice

[BRLAMustang]

New to the forum. Recently acquired a 2011 GT with 14,000 original miles. Car runs very well with the exception of a little bit of a irregularity in the idle when sitting still. Nothing major. None the less, thinking it might be time to address a few things such as changing the transmission fluid, coolant, and spark plugs (all are original from what I can tell). Suggestions on whether or not the fluids need to be swapped and best plug to run. Only mods executed so far are a Steeda CAI and a Magnaflow 3" exhaust with high flow cats and mufflers. Thanks for your time and attention!

 

[delroy]

I would most definitely change the coolant. It's easy and not expensive. Use only distilled water plus a quality coolant. I have a similar situation, just bought a 2014 GT with low mileage. When I drained the rad only 5 L came out. I did not make any effort to drain the rest. Total capacity is approx 13 L. I filled with 50:50 Prestone. I will repeat 2 or 3 more times. You can do the math to see how much of the original coolant remains in the car after each drain and fill. As for the ATF and the plugs, you will get lots of conflicting advice. I think you have an auto trans. (?) Make sure you know what you are doing with your transmission, but it's not rocket surgery.