The Xplora has a hiccup

[4rd Xplora]

Despite having 300K + on her, my Explorer 4.0 ohv, has run like a day 2 job. Recently while driving home on Interstate 35 at about 70-80 mph, I kept hearing a odd noise. I rolled the window down and lowered the stereo and was surprised to hear labor knocks coming from the engine. She runs fine and is giving 17-19 mpg on the average and if you didn't hear the noise you would never know it from the engine's performance. Changed the oil today and rear shocks. I power braked the engine enough to break the back tire loose and heard no rattle. Now my question is should I run some Barryman B12 thru the engine due to the fact that the mill has GOT to have some carbon bill up in the cylinders after 20 years and could carbon bill up be the problem by changing the engine's compression ratio? And what are the draw backs, if any, from cleaning the cylinders in this manner?

 

[koda2000]

If it is pre-ignition knock, I'd first try using a higher grade of fuel (mid-grade or premium) to see if the noise goes away. With 300k+ on that engine it probably has carbon buildup on the valves, heads and pistons. This effectively raises the engines compression. A higher grade of fuel should stop the pre-ignition knock. I doubt running anything through the engine will make any difference, but I'm not much for "miracle cures" in a bottle. If I was going to try anything I'd put in a couple of bottles of Chevron Techron through it.