Originally Posted by goalie35

I just got my 370 used. The dealer has it as a "Certified" used car and did an oil change.. Great EXCEPT they used reg oil not synthetic..... after running a long trip at higher speeds i got the dieseling sound... checked and found a response that the oil viscosity break down caused the tensioner to slip... Well dont know about that but replaced the oil with synthetic and noise went away... So low octane from the quick gas may have an effect but it only stopped for me with the changing of the oil.. as i used the same on the road gas 93/94 for my last trip and NO NOISE... Love this car.....