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Convince me to change my spark plugs every.....

Old 06-12-2019, 07:14 PM
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Default Convince me to change my spark plugs every.....

Hey guys,
On a four stroke newer outboard...how often do you change your plugs? Only if they look like they are worn under inspection or they start missing? Or do you change them every 100 hour service?

Personally, I can't wrap my head around changing them yearly. I mean, even though I realize that a car engine isn't exactly the same as an outboard, I can't figure why there is soooo much of a difference to the point that outboard plugs shouldn't last close to the same as a car. Which brings up another question...

Generally speaking, how do miles on a car equate to hours on an Outboard? Lets assume for arguments sake that most 4 stroke outboards should get at least 2000 hrs and most cars should last at least 150,000 miles.......does this mean that each hour on an Outboard equate to 75 highway miles in a car? This would make since that a 100 hr service would be on par with a 7500 mile oil change. And if that is at least close...then since many cars go 100,000 miles without changing plugs then shouldn't and Outboard get at least 1000 hrs on a set of plugs?

Anyway...I know my above reasoning is faulty and I expect you guys to set me straight, so let me have it
Old 06-12-2019, 07:19 PM
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Plugs every 300. Oil, lower, fuel filter every 100. Belt every 300.
Old 06-12-2019, 07:49 PM
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I;m right there with you. I can't imagine changing my plugs every 100 hrs. I go until they show signs of wear, then I go further. I can't tell you how many times I've changed plugs expecting a change and get zero performance increase.
Old 06-12-2019, 08:11 PM
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Depends how you use the boat. If you spend a large percentage of your time at cruising speed, then you're turning 4,000 to 5,000 most of the time while the car is only doing maybe 2,500-3,000 (and at a much lighter load). That means your spark plugs are firing twice as much and under a much higher load.

If you have fully-closed loop system (as O2 sensors) then I'd say you're fine extending the interval to 200-300 hrs, but I wouldn't go much further. You should NOT notice a change in performance because you're trying to do it BEFORE it becomes a problem that impacts performance which could have other deleterious effects on the motor.
Old 06-12-2019, 09:00 PM
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Marine use is much harder on an engine than the average car. Sitting unused for months, and then fired up and run-ing at 4000 to 5000 RPM. I do my plugs about every 200 hours.
Old 06-12-2019, 09:11 PM
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Plugs aren't expensive
Old 06-13-2019, 02:55 AM
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I used to have a 2005 Optimax for 10 yrs. and a 1000 hrs. pulled Plugs at 300 hrs. and they still looked new! They run Iridium Plugs like most Cars now days.They last a long time.
Old 06-13-2019, 03:10 AM
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Originally Posted by homeby51 View Post
Personally, I can't wrap my head around changing them yearly.
You are not alone - it would seem the Yamaha engineers are of the same mind.

The Recommended Maintenance Schedule calls for 100 hr/yearly inspection of spark plugs -

OR "replacement as necessary".

Unlike some other maintenance items, Yamaha gives no defined period for outright replacement of spark plugs.

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Old 06-13-2019, 03:32 AM
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Originally Posted by jheiii View Post
Plugs every 300. Oil, lower, fuel filter every 100. Belt every 300.
Belt? Are you referring to your timing belt? Hopefully you are not changing that every 300 hours.
Old 06-13-2019, 03:34 AM
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My plugs have always looked like new at the 300 hr change.....I see no reason to change any more often than that.
Old 06-13-2019, 03:35 AM
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I change plugs every 300 hrs. and the old ones look like new. But what I have encountered is difficulty in removing the lower two plugs, on a V6 3.3 F250, and this would concern me about extending the interval beyond 300 hrs.
Old 06-13-2019, 04:09 AM
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Originally Posted by tarpononecharter View Post
Belt? Are you referring to your timing belt? Hopefully you are not changing that every 300 hours.
I am thinking alternator...…….
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Old 06-13-2019, 04:55 AM
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I just changed my plugs in a Yamaha 150 for the first time a couple days ago (haven't been back out yet). Bought the boat new in April 2010 and it only has 210 hours on it. Almost all of the hours are at cruise speed and while it ran fine, it would shudder just a little at idle. Changed all the fuel filters, etc at the same time. Oil/gear oil/filters get changed every other year since I only average about 20-25 hours a year on it. (boat sits in a HVAC garage when not in use so condensation/elements issues are greatly reduced)
Old 06-13-2019, 04:57 AM
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I've had good luck changing my spark plugs every 500 hours on a F150.
Old 06-13-2019, 05:04 AM
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Don't go ballistic into other extreme. You don't want rusted is plugs that are stuck.
As far as longevity goes one word iridium...
Old 06-13-2019, 05:14 AM
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Originally Posted by tarpononecharter View Post
Belt? Are you referring to your timing belt? Hopefully you are not changing that every 300 hours.
No, referring to the accessory drive belt. Manual calls for every 300 hrs. This is on a Mercury outboard, 90HP 4 Stroke EFI.
Old 06-13-2019, 05:15 AM
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"If it ain't broke, don't fix it"
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Old 06-13-2019, 05:30 AM
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Originally Posted by Kaper View Post
You don't want rusted is plugs that are stuck.
Right.
Which is why -
just as with the thermostats, water pump impeller & housing, 'poppet valve', and anodes -
the schedule calls for yearly inspection.
Not necessarily replacement.

Even if not replaced with new parts,
removing, and re-installing,
ensures that they do not corrode and seize in place.

Old 06-13-2019, 05:35 AM
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Originally Posted by Fwpratt View Post
Right.
Which is why -
just as with the thermostats, water pump impeller & housing, 'poppet valve', and anodes -
the schedule calls for yearly inspection.
Not necessarily replacement.

Even if not replaced with new parts,
removing, and re-installing,
ensures that they do not corrode and seize in place.
No kidding. I am doing maintenance to my F115 that the previous owner never did. Anodes for one. Next is t-stat and poppet valve.

As far as all the comments about “my plugs still looks good” how do you know it’s still working at 100%. How do you know it’s not going to fail next time out. The way a spark plug “looks” has no bearing on if it’s working or not. And they are cheap.
Old 06-13-2019, 05:37 AM
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Originally Posted by Kaper View Post
Don't go ballistic into other extreme. You don't want rusted is plugs that are stuck.
As far as longevity goes one word iridium...
That's a good point, IMO. Maybe I need to break them free and lube the threads every year? Also, that's the reason I change my water pump impeller....so my drive shaft don't stick to my power head. I realize I don't have to change my impeller, but I do it anyway even though it looks new when I throw it away.

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