Strange spark plug coloring on a LandRover.
 

A co-worker was just showing me the plugs from his V8 Discovery. The plugs looks nice and brown on one half and the other is black. Has anyone an idea as to what this is from? He is thinking the ejectors.

Is it carbon build-up from running too rich?

Or maybe burnt oil from a leaky gasket? IIRC The Rover K series engines are renowned for gasket problems.

I think it would have the same black color all the way around if that was the problem. Only half the cone is black on these plugs. It is something directional.

put the plug in the engine as normal, and mark on the plug which direction each valve is towards it. match up the black and brown to the marks that represent valve locations.

if it is truly directional, it pretty much has to be related to one of the valves. this would let you see which valve it is that's most likely related to the problem.

Well that would be difficult to do now since all the plugs are out and which one came from what hole is not known.......

What do you think the problem would be with the valves? This engine is a push rod job and I think it only has one intake and exhaust valve per piston.

if I had to guess, I'd put my money on burning oil. perhaps he's sucking in oil through the intake, thus messing up the one side, then it gets burned and exhausted before it can mess up the other side? I'd want to ask a host of questions first. how old is the car? is it known to burn oil? were all the plugs this way or just a few? is the engine running alright or is it a little hurtin'?

Does the black wipe off, like soot, or is the ceramic itself discolored? If the former, I'd strongly suspect that the plug wasn't properly seated and that bypass gasses were the culprit.


dcb

Well he bought it sight unseen over the internet for about $3500. The AFT line was crushed and blocked so he replaced that. Then he found it had a bad tranny and he got it rebuilt. Then he found the thermostat was stuck open and he replaced that. Now he finds the front idler rod is bent and has to replace that before the wheel alignment.

All 8 plugs look exactly the same. Too early to tell cause he has only driven it 120 miles.

I do not see how blow by past the plug seat could do this.

You're right; not on the plug tips. I re-read your original post and don't know where I got it into my head that you were referring to the OUTSIDE of the plugs. Sorry to add to the confusion.


dcb