Does this sparkplug look normal?
 

I posted the following on the engine rebuilding forum, but didn't get any responses so hoped I would be a little more successful here.

I purchased an 86 Carrera last summer with about 85k miles. I had a PPI performed that showed very good leak down and compression. Thought I was in good shape, but oil consumption may be higher than recommended. I say 'may' because I have been chasing a few leaks - return tubes, valve covers, etc. - that have prevented me from getting a good number. Plus, I have only put about 1,800 miles on it since the purchase.

The PO told me that he replaced the plugs just before I purchased the car. Quite frankly, I wasn't smart enough to ask about his oil consumption, but don't know if I would have gotten a straight answer anyhow. I pulled a plug today to see what it looked like. It has less than 2,000 miles on it, so relatively new.

This is my first Porsche, but have done lots of tune-ups over the years. The electrode (greyish brown) and insulator (fairly white) look pretty normal to me. I was a little concerned about the dark carbon-looking color at the base of the plug, just before the threads start. The dark deposits flaked off when I scratched them with a blade.

I'd appreciate anyone's thoughts. Thanks.

http://forums.pelicanparts.com/uploa...1202084263.jpg

Greg,

That plug looks OK albeit perhaps a tad lean unless the engine idled for awhile.

When reading spark plugs, the only part that matters is the insulator color, deposit composition, and the position of the "fire ring" or band on the insulator. Thats somewhat subtle in nature and takes an experienced eye to see and interpret.

To really get a "snapshot" about what goes on in the engine, one must perform a proper plug cut and that involves holding the engine RPM at a certain level while cutting the ignition. One then coasts to the side of the road and plug all the plugs to read them. If one knows what to look for, this is a very accurate "window" into the fuel mixture, timing and fuel composition of what goes on inside there under load. :) :)

Keep an eye on the oil consumption as that tells you the condition of the valve guides.

"Keep an eye on the oil consumption as that tells you the condition of the valve guides."

Steve - Thanks for the response. The engine was idled for about 30 seconds prior to shut down.

If I am understanding you correctly, the plugs can't tell me much about oil consumption. I was trying to determine if the plugs might verify or not verify that my car might be consuming oil. Between the leaks and the few miles I driven it, I haven't been able to get a good measurement yet.

Greg there is no oil on that plug that I can see. Like Steve said, plug looks fine. why don't you just tell us how much oil the engine has used since you got the car.

"Keep an eye on the oil consumption as that tells you the condition of the valve guides."

Steve - Thanks for the response. The engine was idled for about 30 seconds prior to shut down.

If I am understanding you correctly, the plugs can't tell me much about oil consumption. I was trying to determine if the plugs might verify or not verify that my car might be consuming oil. Between the leaks and the few miles I driven it, I haven't been able to get a good measurement yet.

Looks OK, and you could go to the next cooler spark plug.

I agree with the consensus here that the plug looks fine. The Grand National and T-Type Performance Enthusiasts website has an excellent article called Spark Plug Firing End Analysis that you might want to take a look at or bookmark for future reference. There are lots of good pictures to help you see what you are dealing with.

Here are mine for comparison. 1987 with significantly higher miles at 160,000 and oil consumption of 1 qt every 700-800 miles. Here are my plugs. Replaced them all because #6 (upper right) had foulded out and I was getting no spark in that cylinder.

http://forums.pelicanparts.com/uploa...1202160545.jpg

It looks fine + clean of oil. I wish mine look like that.

Coupla thoughts......

1.) With the advent of lead-free gas...the "art" of plug reading has vanished and I'm not so sure anymore that one can accurately still "read" plugs.
2.) Black soot that comes off easily might just be a "babied" engine. Go drive the snot out of it for a while....like any Porsche should be driven.
3.) As to oil consumption...or the "apparent" high oil consumptioin you may find. Make sure you're not getting side-blinded by an appearance of high oil consumption, which can occur if you fill to the "full" line. If you do check oil level ( engine idling at 800-900 rpm, oil "at temp", flat level ground)..fill only to the "middle" mark or even a smidge below. Too high and the excess oil ( when hot) gets into the intake tract...gets "consumed"...and you think..."OhMyGod....I've got high oil consumption and bad guides"...when maybe..... you don't.

Mark,

Mine look pretty much like yours.
Just wonder why #1 and #4 usually look best while #3 and #6 worst.
Is it because of the different distances from the fan and cooling effeciency?

Hi Wil,

LOL,..Spark plugs "reading" has not vanished; they simply look different when using unleaded fuels and one must know what to look for and look at,...:).

One must ignore the black ring of soot on the shell as thats one of the byproducts of burning unleaded fuels and means nothing at all.

Thank you to all, I have learned a great deal from this brief thread.

I was obviously refering to the first picture on the thread (single plug).

The other picture showing the entire set of 6 is a totally different story...

so true. same on mine. I think its because 3 and 6 are the most awkward to get at and replace ;)

Paul,
Plugs from cylinders #3 and #6 in my Carrera still looked bad after several replacement so I guess there was probably some cooling problems during its 20-year history resulting in worn piston rings and/or valve guides.

BTW, I like your sign of 9-eleven very very much!