I appreciate your bringing your clicking sound of the 2.7 liter motor to our attention. There is somewhat of a history of the timing chain tensioner going bad in these motors. The result is that the chain is operating with considerable slack and actually slapping the chain cover. The danger here is that the chain becomes loose enough to jump a tooth on the sprocket and put the motor in a serious out of time situation that can cause motor failure. It is up for debate to whether or not constricted oil flow to the timing chain has caused these tensioner failures or whether the tensioners have worn out or binded up from a lack of lubrication or whether it is the design itself.
The 2.7 has had some lubrication issues, mainly due to relatively small oil galleries, with bends close to 90 degrees, which lends itself to constriction from oil related deposits. It is imperative to be on top of oil change intervals and keeping the oiling system clean to maximize the useful life of these motors.
Bottom line is that I can not tell you for sure that the ticking sound is coming from the timing chain slapping against the timing chain cover. It could well be a morning ticking sound from a somewhat dirty hydraulic lifter, causing a time lag to pump up adequate pressure to operate a valve or two too optimum.
The current oil fill of Pennzoil high mileage is compatible with Auto-Rx. Perhaps not as good as just plain old Pennzoil in the yellow bottle. High mileage oils tend to include ingredients that help to swell or make pliable old motor seals by the inclusion of some ester technology. Ideally we like only Auto-Rx to be the only or at least dominant ester group for maximum cleaning. All esters are polar, which means they have an attraction to ferrous metal surfaces. So in essence you have a combination of esters competing for the same metal surfaces. However, with that said, as long as you were to run the rinse phase of the Auto-Rx application, with the Pennzoil or other plain conventional oil, you would get good cleaning results.
So yes, you could start your Auto-Rx application by adding into your existing oil, just rinse with a conventional oil. Also I might advise that you have the timing checked on the engine to see if there is in consistency from a worn or wandering timing chain. Again I dont know whether or not it is related to a stretched timing chain, the tensioner is bad, or whether or not the flow of lubrication to the chain and tensioner is being constricted. It could well be that the tensioner which uses spring pressure is bound up with oil related contamination, or whether or not the tensioner is just plain worn out.
In any event keeping the 2.7 liter motor clean is imperative to having it last in the long haul.
