Why replace spark plugs?

[steam_mill]

So, I regulary replace my spark plugs. My question is why do spark plugs require replacement.

What I mean is that if they are cleaned, gapped properly is not a surface gap plug and put back in the motor what's the difference between a new plug and a cleaned plug.

Sure, I understand that elecrodes wear down eventually. I generally replace my plugs every two years on my 2003 90 hp. I replace the plugs every year on my 2000 Mercury 9.9.

I don't see a difference with the new plugs. I clean my 9.9 plugs at least twice a season.

Is there some internal items that wears down?

 

[lowkee]

Re: Why replace spark plugs?

I'm no spark plug engineer, but here is my understanding of them.

The electrode wearing down and the ceramic cracking are the only two items which cause plug failure. It is more obvious in standard plugs, but the newer platinum plugs make it more difficult, as the electrode is often a fine wire within a larger 'housing' and at first glance it appears it never wears down. The ceramic is much tougher to detect, as it may crack internally first, causing the plug to run sometimes much hotter.

The 'change your plugs every xx miles' notion is mainly blanket maint advice. Different plugs last a different lifetime. The plugs in my Neon last about 30K miles, where the plugs in my truck last 100K or more. It all depends on the makeup of the plug electrodes. Gapping your plugs correctly also extends the life of them, as over-gapped plugs fire at a much higher voltage, which wears down the electrodes faster.

 

[Snowfish]

Re: Why replace spark plugs?

I figure fresh sparkies, in my boats & sleds, is cheap insurance. Pretty much guarantees the hottest spark possible provided the rest of the system is functioning properly. Since I don't get to use my toys, as much as I'd like, it's less hassle to replace than wondering if I should have.

My cars & trucks get new sparkies every 2 years max. It can get -20 degrees (-39 last winter while leaving to go ice fishing. That's a little harsh) or more in the winter. Again, cheap insurance that things will start.

 

[rcmickey]

Re: Why replace spark plugs?

I have to agree with you Snowfish! I do not like to leave anything to chance. When your out in the ocean the last thing you want is a bad plug to spoil your day. I do have a question though, what is a surface gap plug? Ane how would you gap it?

 

[hazwild]

Re: Why replace spark plugs?

I think just like most things on a boat you replace them just for the piece of mind of not breaking down at sea.

 

[CharlieB]

Re: Why replace spark plugs?

Electricity takes the path of least resistance.

Fuel is NOT 'clean', it leaves residue from combustion. Two strokes are also dependent on lubricating oil in their fuel mixture, which contributes to residues, by-products of combustion.

These deposits (ash) build up on the plug surfaces, a measurable amount of carbon is included with this ash. Carbon is a very good conductor of high voltages such as those used to create a spark, thus electricity taking the path of least resistance, follows the carbon path to ground instead of arcing across the spark plug gap, shorted out.

The ash can 'fuel foul' which is saturating the ash layer with fuel enough that the plug is 'shorted out'.

 

[sunburnt]

Re: Why replace spark plugs?

i notice a bad runner one time on a 1986 2 cyl. from water just hitting plug looked great but lost some continuity. internally only slight resistance on meter. checked every thing. ruined 2 days vaca when i only needed plugs! weak spark .always ngk on my 2 cycles. seen too many bad others. brand new head aches