Who's good at reading spark plugs?

LaRea

Anybody want to offer opinions on what these spark plugs say about the health of my engines?  @212rowboat, @69fastback ?

2007 Rinker 370
Merc 496 engines with 800 hours
Plugs have 300 hours
[EDIT:  plugs are AC Delco 41-983, platinum plugs]

After replacing plugs and wires this weekend, I noticed an immediate bump in performance.  Cruise MPG improved by about 9%, getting back up to what I recall seeing a few years ago.  I attribute the improvement to the wires, not the plugs.  The wires were probably original, and two wires had severe chafing damage.  

A few things I noticed about the plugs:

• S8 is cleaner than the others.  That's one of the plugs with a damaged wire.  It's possible the plug was not sparking at all. 
• S4 is a little bit shiny.  Oil fouling?
• P3 has some crusty buildup on the side of the insulator.
• P7 has corrosion on the outside ... maybe a water leak that I need to investigate.    

davidbrooks

I am interested also. I just posted another set of plug pics on another thread a few days ago. I would think you would want to look at your new plugs vs these. With a new set of wires the new ones could look quite different. I had about 150 hrs on my pkugs and also saw a marked improvement and that was putting in cheaper plugs. I pulled out the NGK Iridium.

Aqua_Aura

S8 is not firing. S4 looks like oil possibly a leaking valve. P7 looks like maybe it got saltwater on it 🤔 P3 maybe running rich but I'm sure someone more knowledgeable will chime in. Is this carburetor or injected?  

aero3113

LaRea

Injected.  I wish I had kept track of which wires had chafing damage.  S8 was one, and there was another one on the starboard engine.  I think this was S8:

PickleRick

I've met a few guys who can tell you ring wear oil consumption or valve seals, valves not seating, etc 

My speciality is 2 cycle so I only worry about grey plugs(lean)  i want charcoal wet ground straps. No valves or oil rings to worry about.

Ill also be following this thread closely. 

LaRea

Old and new.  These are AC Delco 41-983 (platinum, not iridium).  None of the plugs had any major change to the size/shape of the center electrode.  And remember, the plugs only have 300 hours on them.  I only changed them because I was doing wires, and it's not much extra work to change plugs too.  

Handymans342

Sorry, I can’t help. Diesels have no plugs. LOL

Aqua_Aura

I wouldn't say only 300 hours. That's like putting 50k miles on a car (my educated guess) could be more or less depending on how you run the boat. I think 300 is the change interval as well. 

PickleRick

Handymans342 said:

Sorry, I can’t help. Diesels have no plugs. LOL

Liar...they have glow plugs.

PickleRick

Aqua_Aura said:

I wouldn't say only 300 hours. That's like putting 50k miles on a car (my educated guess) could be more or less depending on how you run the boat. I think 300 is the change interval as well. 

How do the efi motors do at idle/trolling speeds vs carbed?  Even with my Holley dialed in by one of the best in the carb industry i still needed some wot after long idle times to clean the plugs.

Aqua_Aura

I idle every time I go out for about 20 min since the channel is no wake out of the marina,also I leave it at idle tied up to get to temperature and make sure all is well. It runs perfectly smooth for me. Never have to power up to clear up the motor. Just like a EFI car it takes care of itself mostly. 

I did the plugs when I got the boat from someone who probably couldn't spell maintinince and they looked all normal and matched. 

LaRea

Although I do a lot of 1000-RPM cruising, my last run before changing plugs was 3 hours at 3900 RPM.  And I do enjoy a few minutes at WOT every now and then.  

Handymans342

PickleRick said:

Handymans342 said:

Sorry, I can’t help. Diesels have no plugs. LOL

Liar...they have glow plugs.

My Yans didnt

PickleRick

Handymans342 said:

PickleRick said:

Handymans342 said:

Sorry, I can’t help. Diesels have no plugs. LOL

Liar...they have glow plugs.

My Yans didnt

Did it have a probe in the intake or engine mount fuel filter assembly?  Usually they have some place to heat fuel or air when operating at or near freezing temps

Handymans342

Never freeze in Florida 

PickleRick

A couple of years ago it got down around freezing in the keys.  The iguanas were falling off the trees.

A guy picks them up for food or maybe bait.  Once they warm up they come to life and go ape $hit all in this guys car and causes him to wreck.

Black_Diamond

300 hrs on a set of plugs is a lot IMO. Consider you are running 3-4x the rpm over your car while on the hwy. 

LaRea

In one of the other threads, @Alswagg said the Merc recommended service interval is 500 hours.  Maybe that's for iridium plugs.  

PickleRick

Iirc 100 boat hours = 10,000 miles.  

500 hrs on a set of plugs sounds about right on new efficient efi motors.  300 wouldn't hurt.    

69fastback

Hard to get a good reading on plugs without being able to see down in them. 

LaRea

Ahh ... hopefully these are better.

69fastback

Definitely better. 

I’d say, overall, those look pretty good for 300 hours. S8 definitely looks a tad lean. Looks like P3 May have some valve seal/guide seepage. 

LaRea

Better pix of P3 ... definitely the odd duck of the group.

Ian

Handymans342 said:

Never freeze in Florida 

Of course it does, thats why they spray the fruit trees with water so it freezes and protects the fruit to sub freezing temps. Maybe not last year but I think the year before.

Florida ain’t the paradise Floridians want it to be...

YYZRC

Here’s mine. #2 will be done when I flush my heat exchangers - just waiting on the end gaskets to come in. 

YYZRC

There was a lot of rust that flaked off on the underside of the manifold at the stern (plugs 7 and 8). 

LaRea

How many hours?  The insulators look cleaner than mine.  I had manifold rust near P7.  

YYZRC

I have no idea. Boat has 550 hours total. I’m guessing the plugs and wires were original since the wires have some red and green tape on them. Did the cap and rotor. Will save wires for spring. 

Aqua_Aura

Anyone know when Merc went to electronic ignition? My Volvo is an 06 8.1 so no cap and rotor. I was just surprised to here cap and rotor still on the post 2000 engines. 

YYZRC

Starboard motor hasn’t been running well. Pulled the plugs today and one was bad. Used this thread to help diagnose!