Spark Plug Condition

[rpowers]

Hi,

After 6 months of running on these plugs, I changed them for new ones (see Freeze Plug Issue thread).

I found plugs 1 and 2 to be in normal condition, but plugs 3 and especially 4 had more black soot-oil, and plug 4 was wet and smelled of gasoline.

What does that say about how the engine is running?

Thanks!

[jhwelch]

Unrelated to your question--after just 6 months why are those plugs so rusty, and I note
some discoloration on plug #2, too.

[rpowers]

See thread on "Freeze Plug Issue".

Salt water leaking onto top of block, pooling in plug depressions...

Before and after photos below:

[marthur]

In general, a gray or golden brown dr sooty look on all 4 plugs is normal, so I agree that 1 and 2 look good.

The gas on number 4 could arise simply because that cylinder was on the compression stroke and had drawn a charge of gasoline into the cylinder when the motor was shut down. I have seen that on my motor when changing plugs, especially if the motor had been run recently.

In late model engines, the rear plugs can be cooled more than the front two cylinders if too much cold raw water is directed to the rear of the engine by the diverter cap. On my engine, the back 2 cylinders tend to run a little cooler than the front two and will carbon up first / more under any conditions that cause plugs to foul.

However, one or two plugs with a black wet (gassy) sooty look and the other two plugs normal can also indicate that something is going wrong in the two affected cylinders. Such as bad spark plugs or bad plug wires or distributor cap.

Low compression on the affected cylinders can also promote carbon build up. If the two bad cylinders are next to each other (like 3 and 4), a partially failed head gasket may be indicated.

Your #3 plug doesn't look wet, so I would check these items out.

Don Moyer also says that a black oily sooty look can indicate worn or broken oil rings on the affected cylinder. (As opposed to all four plugs black, oily and sooty, which would more likely be exhaust backpressure is elevated to 5 psi or higher). I have no experience with bad rings, so I can't comment on the look of your plugs.

[rpowers]

Thanks for the excellent advice.

I'll check my new spark plugs/wires after a few hours of running, and see what they look like.

cheers!