What used spark plugs should look like

[fc3]

One can tell a lot about the general state of an engine by looking that the old, used spark plugs when they are removed. Additive fouling, overheating, detonation, oil consumption, and other things can be deduced from the condition of old spark plugs. You can find examples in most shop manuals. Here is a photo of eight plugs I just pulled that are show normal wear and deposits on the electrodes and insulator. The light tan color is the result of normal combustion.

About the only thing wrong with these is you can see where I was sloppy with the anti-seize compound on the metal body when I installed them a few years ago.


Best regards,
Frank C

 

[Weave]

As usual, good info Frank. How many hours on those bad boys?

 

[Dave S]

Where is the other eight? :wow:

Just kidding Frank............those plugs look good.

 

[fc3]

They are not from the boat, they're from my Navigator. Should be a bit over 100,000 miles. I think I put these in just a bit under the 200k mark and pulled them today with about 300,200 on the odometer. Taking a W.A.G at average speed there must be over 3,000 hours on them.

Best regards,
Frank

 

[Dave S]

Is that 300K without a tear down or a rebuild?

 

[osd9]

I was in my ER for over an hour and I looked all over and I still can't find the spark plugs....:huh:

 

[Four Suns]

I was in my ER for over an hour and I looked all over and I still can't find the spark plugs....:huh:

They are right next to the stink generators.

 

[osd9]

Oh!!!!!.....That's why.....I didn't notice becasue I winterized my stinkers with fogging oil!

 

[carterchapman]

MM replace mine at 150 hours when I bought the boat. How much you bet they DIDN'T use anti-seize?

I'll pull 'em this fall and check.

 

[fc3]

Is that 300K without a tear down or a rebuild?

Yes, except for the replacement of the valve cover gasket back in 2006, the engine has not been touched.

MM replace mine at 150 hours when I bought the boat. How much you bet they DIDN'T use anti-seize?

Only need anti-seize on aluminum heads. Your boat probably has cast iron, so it's not really necessary. Actually, I probably did not need to use anti-seize. Not sure if I'll make it to 400k. We'll see.

I was in my ER for over an hour and I looked all over and I still can't find the spark plugs....:huh:

Umm, check again. I did post this in the Gas engine forum.

Best regards,
Frank

 

[carterchapman]

Thanks Frank,

I agree about the cast iron, but I still use it anyway as it is easy to apply.

 

[jitts3]

Frank's right. The story of an engine is written on the plugs.