First time poster, please be gentle. I have a 2002 Ford Explorer. My mechanic just ran a cleaner through the engine and added a mild detergent to my 4.0L V6. I was having a problem with the chain tensioner, and this actually reduced the noise for the first 500 miles. The noise is now back, and so is a new problem. I am having a blue puff of smoke when the engine starts after sitting for a while. It clears up in 1-2 seconds. The mechanic used quaker state, or what I now refer to as devil juice, on the oil change. I want to switch to the best oil for my situation. Just a shade under 100,000 miles on my X. I was looking at Valvoline MaxLife, but I am not sure whether to use a full synth or synth blend. I just bought the vehicle 10,000 miles ago. I do not know what was used prior to the purchase. Will changing to a synthetic result in more problems than cures? Let me know if you need additional information. Thanks in advance.