View Full Version : Reading Tea Leaves, er... Spark Plugs?

09-20-2006, 09:59 PM
I changed the spark plugs in the '87 325iC last night. I've only had it for a couple of months so I don't know the last time they were changed. I've heard you can learn a lot by reading the plugs. Besides the fact that my valve cover seal isn't so hot and it's leaking oil down onto the plugs from the outside, what can you learn from looking at these? Sequence is back to front of engine from left to right in the picture. I think #6 has more build-up than the rest. Is that significant? What else can you see?

http://www.georgeco.org/images/bmw_plugs_sm.jpg (http://www.georgeco.org/images/bmw_plugs.jpg)
[Click image for larger version]

09-20-2006, 10:15 PM
Yours look a lot like the ones I just took out of my '87. No idea how old the plugs were but I had the oily/watery sludge around the insulators, too.

I'm no expert, but these look like pretty clean and consistent. Maybe the tips are a bit burned on 1 and 4?

09-21-2006, 09:51 AM
plugs look like they've been in there a while. A little bit of fouling on a couple, but nothing too bad. Biggest thing I see is that they were probably the wrong plugs (autolite, from what I can tell) Having experimented with NGK (very briefly), I stick to the Bosch W8LCR plugs that the car came with. Just changing back to them should make a difference. NEVER put platinums in an M20--they really don't like it.

Do yourself a favor and change the valve cover gasket--they're cheap. The oil on the outside of the plugs will affect their temperature and might mess with your spark. If you haven't done it in a while, you might as well adjust the valves since you'd be taking the VC off anyway.