need2fix99

I was doing a simple tune up on my 98 4cyl frontier and I found oil on 1 of the spark plugs. (in the combustion chamber) Is this a big problem? It looks bad! Any help would be great. Thanks

RatioCynic

Wet or dry oil on the plugs has many implications. Is this fouling wet [glossy black & sticky] or dry [dull black & sooty] oil on the plugs? Some possible problems are:
Worn piston and rings, cylinder bore and/or valve guides.
Sticking valves
Faulty ignition supply [though all four plugs would have fouling. Although that one plug wire could be bad.]

This plug is the same type/rating as the other three?

Also consider the condition of the electrode, insulator and firing end, e.g. slightly rounded edges [normal] or obvious eroded/melted metal and/or missing insulator surfaces. This may indicate other problems. RC

1997XETruck

Was the oil on the threaded end of the plug? I'm not sure of the design on the 98 Frontier, but I think it's similar to the Q45 in that the spark plugs sit down in a cavity in the middle of the head. If you remove the rocker cover (valve cover) there are RTV seals around the spark plug cavities. The seal at the top of the rocker cover can leak causing oil to run down and around the outside of the plug. When you remove the plug it can sometimes look like oil on the threads depending on how much oil puddled up around the insulator and sockets. Is the end of that spark plug wire boot oily? If so check to see if you notice baked on or oily residue running down the inside walls of that spark plug cylinder... if so then the rocker seal is your problem.

Heath

__________________
1997 Nissan XE Truck - 133,000 Miles
1990 Infiniti Q45 - 91,000 Miles
2005 Infiniti G35 Sedan - 34,000 Miles