Iridium Spark Plugs Anyone?

[Texasmark]

I have a new to me, 2002, 115 HP, 2 stroke Merc. 4 cyl 2+2 engine. Playing around with it I've been learning how it works and what I could do to make it better. I decided to put in new fuel pump and accelerator kits, noting that the old diaphragms were much stiffer than in the new OEM kits so the new ones should pump better. I set the injector gap to 0.20 rather than 0.30 as I wanted the bottom two to kick in earlier than the Serv. Manual setting specified.

I don't run long periods of time at WOT. Mostly in the lower rpm ranges and a lot in the area where I'm running on just the top 2 so plug fouling is a problem, especially the lower 2 (yes the OEM oil injector is working fine) and I run 91 octane regular gasoline with the engine being rated for 87.....I figure that's one reason for the 8 heat range in the recommended plug.

I got a tip from a guy on a tractor forum that used Iridium and premium fuel in his lawn mowers and thought I would give it a try. Results were stellar. Moving on, I decided to get a set for my 2+2, and I was already using 91 fuel. Went to the NGK plug catalog, down around page 268 (recalling) I found Iridium plugs, cross referenced my OEM Service Manual recommended plugs for dimensions and heat range (with a couple of changes listed below), gapped them out to the 10 mm required setting (0.040 in.) like my recommended plugs, and WOW, what a difference in performance.

When putting around, I tilt the engine up above level a few degrees which (per Merc.) keeps fuel from puddling in the spark plug area, helping to reduce fouling....yes it does make a difference. I also upped the temp 2 heat ranges....went from an 8 to a 6 (NGK increases heat with decreasing numbers) figuring I could get hotter as an aid to burn off contaminants without having to worry about pre-ignition or excessive combustion temperatures.

Idle is so smooth that I could put a full glass of water on the engine and not spill a drop (waves permitting....grin). Starts, even while sitting for awhile are instant.

If it suits you, might be something to think about.......just be very careful any time you regap an Iridium....the tip is very small and easily broken in the process and you will find recommendations to not regap for that reason...but with a wire gapping tool and some care, no biggie to regap which I had to do as they were at 0.030 and my engine uses .040. Thought about using them at the issued gap but that is down the road since these are already regapped.

 

[racerone]

Fact ---10 mm = 0.400"----Possible misprint / typo ?

 

[Chris1956]

My neighbors Optimax specified Iridium plugs as std. They also specified they be changed every 2 years. I would expect you to have a similar maintenance schedule. At $23 ea, they are a bit pricey.


I had thought that iridium spark plugs lasted a very long time (100K miles in automobiles), but never heard that they were better performers than platium or regular spark plugs. Is that not true?

 

[Sea Rider]

It's a bad idea to play with other heat range spark plugs from what the motor manufacturer recommends. The motor was engineered to run a specific heat range plug.. Just gap the electrode to factory specs if using NGK spark plugs. If said motor fouls plugs you need to run full hammer down when returning to Terra Firme..

Happy Boating

 

[Texasmark]

My neighbors Optimax specified Iridium plugs as std. They also specified they be changed every 2 years. I would expect you to have a similar maintenance schedule. At $23 ea, they are a bit pricey.


I had thought that iridium spark plugs lasted a very long time (100K miles in automobiles), but never heard that they were better performers than platium or regular spark plugs. Is that not true?

I got 4 new in the carton on ebay for $27, fast and free shipping.

 

[Texasmark]

It's a bad idea to play with other heat range spark plugs from what the motor manufacturer recommends. The motor was engineered to run a specific heat range plug.. Just gap the electrode to factory specs if using NGK spark plugs. If said motor fouls plugs you need to run full hammer down when returning to Terra Firme..

Happy Boating

Just like engines that come with props, engines are setup for the motoring public doing anything and everything so you have an averaging type of setup. Certainly design engineers take that under consideration when writing specs for equipment that is to be used anywhere in the world, by anyone, under any kind of conditions....and there can be many. Also the engine is rated at 87 octane minimum....and that could be year old gas where I use fresh 91 gasoline with Mercury #1 snake oil and Pennzoil premium semi-synthetic TC-W3 oil.

As I said, I do mostly midrange, with a 5 minute shake the cobwebs out ever so often if the water lets me so preignition potential problems aren't a problem. Besides, plug mfgrs specify that you need a plug hot enough to burn off the contaminants that foul the plugs and mine weren't doing that, even the two that are pulling the load 100% of the time.

I posted this because I wasn't familiar with this engine when I first got it last summer and I picked up on a lot of negative jibberish about this peculiarity and that.....seems, when you get it to the sweet spot (which was mentioned and was said to happen some times), I really like it....a strong performer. Since these engines were said to be produced for some 20 years, and I have seen lots of them when boating, certainly what I said would benefit somebody wanting more out of their engine.

Thanks guys for the comments.

 

[Texasmark]

My neighbors Optimax specified Iridium plugs as std. They also specified they be changed every 2 years. I would expect you to have a similar maintenance schedule. At $23 ea, they are a bit pricey.


I had thought that iridium spark plugs lasted a very long time (100K miles in automobiles), but never heard that they were better performers than platium or regular spark plugs. Is that not true?

I never ran Platinum so I can't compare. Iridium is hard but over time wears away (per spark plug mfgr. comments) so I can see why Merc. recommends a replacement interval, lengthy at that.

Having a high voltage background, if you have a sharp point vs a spherical one, the electromagnetic stresses congregate at the tip vs a sphere, or any geometry other than a sharp point where the stresses are dispersed around the circumference of the object, increasing obviously at any sharp points....one reason for the optional V electrode tipped regular plugs. Most materials can't survive any length of time if they were tipped as small in diameter as the Iridium as they are too soft and erode too quickly. You'd be changing plugs every month or something of the sort and Jane and Joe consumer wouldn't tolerate that.

There is a given amount of energy fed to a spark plug and if that energy can be made to congregate at a single point, the energy density is much higher and more apt to produce a solid plasma vs other dimensions. The main reason I liked the idea of using the Iridium is that since contaminants on the insulator bleed off some of that energy, if one could supply it on a smaller diameter, sharper point, with the fast rise time one gets with CDI ignitions, you can pretty much forget about bleed off of charge due to wet/contaminated insulators.

My 2009 Dodge PU Hemi ran Champion standard copper tip plugs and the manual said change every 30k miles.....which I found to be a nuisance maintenance item having 2 per cylinder in that V8 and not all that easy to get at to change. My current 2011 Silverado with the 4.8 pushrod V8 came with NGK Iridiums and it's the same plug ID# specified for my 2009 Honda Element 2.4L dual Overhead Cam. No mention in either operators manuals out to the 100k mile service life, is any requirement for changing plugs. My OEMs are still in the truck I bought new (44k current mileage) and the Honda I changed when I bought it last year with it having 100k miles and no idea as to maintenance history.

 

[flyingscott]

Nothing you have done will make.a.difference to the running quality of that motor. . Iridium plugs will do nothing for you and could.possibly cause.detonation.

 

[Sea Rider]

I run myself a much higher octane fuel than what the factory recommends, keeps my pistons and exhaust chamber with less carbon formations in the long run while the motors runs much smoother. With respect to running hotter spark plugs than what the factory recommends, the issue is that plug fouling is due to not reaching their Self Cleaning Temp achieved over 500º C temp.

Running under that temp for longer periods will foul plugs inevitably. All my 2 strokes OB's does same, the difference is that I never troll or run for long time periods at idle or fast idle rpm, always 3/4 to full throttle, that keeps my plugs's electrodes perfectly clean.

Other issue for plug fouling could be that the automatic oil mechanism could be out of adjustment delivering more oil than needed, will need to check the Service Manual specs. Love doing crazy things myself to my motors but never out of their factory tech specs. Good Luck on your experimentation, lets hope that running hotter plugs don't perforate the pistons heads in the long run.

Happy Boating

 

[Faztbullet]

Higher octane fuel does not burn cleaner....its the additives that make it cleaner or its a ethanol base

 

[dingbat]

Octane is a combustion inhibitor.

The higher the octane of the fuel, the harder that fuel is to ignite and the more heat is required to ignite it.

Hotter cylinder temps may or may not equate to burning cleaner.

 

[Texasmark]

Fact ---10 mm = 0.400"----Possible misprint / typo ?

Yepper, Senior Moment, forget the decimal.

 

[Texasmark]

Nothing you have done will make.a.difference to the running quality of that motor. . Iridium plugs will do nothing for you and could.possibly cause.detonation.

Sorry about dat sir. Yes and No.

 

[Texasmark]

Octane is a combustion inhibitor.

The higher the octane of the fuel, the harder that fuel is to ignite and the more heat is required to ignite it.

Hotter cylinder temps may or may not equate to burning cleaner.

It is all detailed in the NGK catalog (https://www.ngksparkplugs.co.za/wp-content/uploads/2019/01/NGK-Catalogue-2019.pdf).....(give it time to load as the PDF is about 300 pages) including cylinder temps, precombustion considerations, insulator temps to burn off contaminants, plugs showing signs of running cold, normal, hot......all right there for the reader to enjoy.

 

[dingbat]

It is all detailed in the NGK catalog (https://www.ngksparkplugs.co.za/wp-c...pdf).....(give it time to load as the PDF is about 300 pages) including cylinder temps, precombustion considerations, insulator temps to burn off contaminants, plugs showing signs of running cold, normal, hot......all right there for the reader to enjoy.

I appreciate of effort, but I’m well versed on the subject from my racing dirt bike days turned performance golf cart tuning as of late.

From a longevity stand point, your better off running factory tunes. Use an additive if your usage doesn’t keep the engine temps up long enough to burn off deposits.

 

[flyingscott]

Sorry about dat sir. Yes and No.

That will be a hard NO. Everybody wants thinks they are smarter than.the.engineers and they are not. I owned my 125 for over 10 yrs change from .030-.020 will do nothing for.you. Although the Iridium spark.plugs will help you. I believe they increase torque by 9000 %.

 

[QBhoy]

I’m a fan of iridium plugs on some engines with enough juice to fire them. Much cleaner burn in some cases and last longer.
certainly saw less build up on my Yamaha 2 stroke jet ski and smoother idle and general running on my 4 stroke Yamaha ski after.
haven’t tried on my 4 stroke outboard, but my Mercruiser MPi V8 inboard has them as a requirement in the manual.
with the latter, I’ve tried the lesser platinum plugs and they just simply don’t do as well as the iridium.
down side is the cost of them. Up side is the longevity.

They won’t suit all motors I’d guess, but made a difference in any I’ve tried.

word of warning though. If you see them cheap...it’s for a reason. There is a real issue with cheap Chinese copy fake iridium NGKs just now. World wide. Have a google at it. Not always easy to spot.

 

[Texasmark]

I’m a fan of iridium plugs on some engines with enough juice to fire them. Much cleaner burn in some cases and last longer.
certainly saw less build up on my Yamaha 2 stroke jet ski and smoother idle and general running on my 4 stroke Yamaha ski after.
haven’t tried on my 4 stroke outboard, but my Mercruiser MPi V8 inboard has them as a requirement in the manual.
with the latter, I’ve tried the lesser platinum plugs and they just simply don’t do as well as the iridium.
down side is the cost of them. Up side is the longevity.

They won’t suit all motors I’d guess, but made a difference in any I’ve tried.

word of warning though. If you see them cheap...it’s for a reason. There is a real issue with cheap Chinese copy fake iridium NGKs just now. World wide. Have a google at it. Not always easy to spot.

Where'd you pick up on that?

 

[Texasmark]

That will be a hard NO. Everybody wants thinks they are smarter than.the.engineers and they are not. I owned my 125 for over 10 yrs change from .030-.020 will do nothing for.you. Although the Iridium spark.plugs will help you. I believe they increase torque by 9000 %.

On changing the gab between the injector housing and the throttle linkage cam, the manual states that the gap determines the kick in point vs throttle setting. It recommends 30 thousandts. I have already proven that it works better for what I do with the boat.

On what engineers do and don't do I am a retired electro/mechanical design engr. of 35 years and know what it takes to design equipment and things to be considered in doing so.

On 9000% torque increase I find that totally amazing.

 

[QBhoy]

Where'd you pick up on that?

The fake ones you mean ?