QuestionMy Jeep has been running great but after my last oil change, the engine is knocking. It has 90,000 miles. Could it be the oil? I used 10W 30. Thanks.
AnswerBill,
Odds are that it's not the oil, as long as you use what the manufacturer calls for (normally on the oil cap too). The 2.5l engine has aways been noisy; when you say knocking, is it a lower end knock, from the area of the oilpan, or up top, in the area of the valve cover? Many components can contribute to engine noise. For example, if it's more of a ticking in the valve cover, there's a good chance that it's a lifter problem. Really, the best way to determine the severity of an engine knock is to take it to a reapir shop that is intimate with the vehicle involved. This may be the last step, since there are a few things to try first.
Some engines develop carbon deposits in the combustion chamber (normally on piston reliefs) that can sound anywhere from a ticking to a knocking. More than one engine has been replaced erroneously for this. The culprit? Poor gas, most times. Some fuel induction cleaners can be effective in clearing carbon from the engine, and even a change in gas stations, over time, can cure this issue. Although I can't advise it, I've *heard* of mechanics dribble water through the intake to break up carbon -- and although it has worked, this can be very detrimental to an engine because of hydrostatic lockup.
Similarly, most fuel additives CLAIM to be able to handle something like this, but IMHO, the only fuel additive worth using is BG 44K. Some others might work to clear this, but none I could recommend.
The best way to fix this is to properly pinpoint the origin of the noise -- if you can figure out where, then the next step is why. If you can't get a handle on it, I'd take it to a pro that knows these vehicles. I'd love to help further, but diagnosing a noise through the internet is impossible. A pro will be able to determine if it's a dangerous engine knock, or something like ignition predetonation.
Good luck!
