Left side of engine filthy

[tobes50]

Well I took of both valve covers to replace the spark plugs when I noticed the back three cylinders are a considarably amount dirtier than the front three, it almost looks like the oil is baked on there. Any ideas why this could be?
Thanks alot, Toby

 

[sdpatt]

I see this quite commonly on engines I have serviced. I believe that since you can see and reach the front valve cover, you can wipe and clean any oil or dirt off that you find. The rear valve cover cannot be reached as easily. The rubber bushings under the washers on the valve cover bolts tend to harden and leak oil over time. This oil is a great dust magnet.

There is always a fine cloud of road dust flying around under the hood when the car is rolling. This dust meets sticky oil and voila - black coating on the rear valve cover. I have also seen this coating on the front valve cover on cars that do not have owners that feel the need to clean the engine. Sad. Very sad.