Spark Plug - Is it normal to have some oil on threads

[the butcher]

I just recently pulled my plugs on my Mercury 115 to check the plugs and while the plugs looked clean, no oil fouling, no carbon buildup, etc... I did notice a bit of oil on the threads of the plugs. Is this normal? The motor is about 2 years old so I am not sure if the factory had sprayed some fogging oil into the spark plug hole when it was new to prevent corrosion/rust since some new outboard motors can stay in the crates for a few years if they happen to be at a small volume dealer... I've had the motor for the 2 years and do annual service/maintenance on it yearly. This plug that is in the attached picture was pulled right after I did an oil change on the motor. All 4 plugs look almost identical to the one in the picture below(eg, no carbon buildup, no oil fouling.. just a bit of oil on the threads). Is some oil on the threads normal? These are original plugs.

 

[adrian1991]

If it was burning oil it would be fouled and all gummed up, I'd say that's more of gasoline residue/varnish

 

[scott craven]

You didn't mention 2 stroke or 4 ?
regardless the plug looks clean, no carbon build up

 

[leaseman]

Plug in great shape in my opinion!

 

[the butcher]

sorry 4 stroke only 2.5 year old motor. So looks like there is no concerns if all 4 plugs look identical to the one in the pic?

 

[kingblazer84]

that plug is perfect almost too perfect.. that center porcelain should ideally be a golden brown but overall great lookin plug! what heat range are they?

 

[YachtMech]

That’s fairly normal, The threads don’t provide any type of seal, so any oil that gets past the rings (which is normal that does happen) can work its way up the threads, the point of sealing is that little compression washer that interfaces with the cylinder head. It’s most common to see it on brand new engines at the first service interval and of course after winterization’s because there has been an oil sitting in the cylinders, but you will see it on plugs that have had Long service life as well

 

[the butcher]

that plug is perfect almost too perfect.. that center porcelain should ideally be a golden brown but overall great lookin plug! what heat range are they?

they are heat range 5. For NGK these are 3rd down from the hottest plugs.

 

[the butcher]

That’s fairly normal, The threads don’t provide any type of seal, so any oil that gets past the rings (which is normal that does happen) can work its way up the threads, the point of ceiling is that little ring that interfaces with the cylinder head. It’s most common to see it on brand new engines at the first service interval and of course after winterization’s because there has been an oil sitting in the cylinders, but you will see it on plugs that have had Long service life as well

thanks Yachtmech. I was confident that the appearance of the plugs from the threads up looked good but wasnt sure why there was a bit of oil on the threads of all 4 plugs. Logic tells me it isnt likely an issue with bad rings or valve seals because what is the chances all 4 have defective rings/seals on a virtually new motor with 110hrs. Also, oil inside combustion chamber would appear on electrodes and top portion of insulator tip. Was sure how oil got on the threads if the rings and valve seals arent defective but your lastest comments makes sense. Yes they are original plugs.

Thanks for all the comments and feedback. Glad its nothing for me to worry about.

 

[hippaisland]

While we’re on the topic. How often do you guys replace plugs in your 4 Stroke OB’s. Do you do it regardless of condition every few years or just based off their condition?

 

[the butcher]

While we’re on the topic. How often do you guys replace plugs in your 4 Stroke OB’s. Do you do it regardless of condition every few years or just based off their condition?

i am on another boating forum and the same question came up...most responses were every 2-3 years. Plugs at the 2-3 year mark should have very minimal if any wear or degredation of the electrodes or any deposits if the engine is in good shape. So based on that info I believe most boaters on that forum replace plugs way well before needing to as a measure of cheap insurance. I plan on changing the plugs out next year which would be about the 3 year mark and apprx 130-140hr mark.

While on the topic, do guys here torque plugs by feel, by rule of thumb such as 1/2-2/3 turn once the plug seats, or use a torque wrench ?

 

[Rockfish]

That plug looks good to me. As for how long plugs last or need replacing I suspect it also depends on the plugs with some of the high end ones perhaps having a longer life span. For my big 6 cyl Opti, the specs call for iridium tipped plugs, as apparently the platinum tipped plugs are not expensive enough.