New plugs how often 2016 Four Stroke 115

[HotTommy]

I will be starting my third season with my 2016 Mercury 115 four stroke next spring. I'm wondering how often I should check or replace the spark plugs. I'd rather leave well enough alone until the time is right. If it matters, its on a lake on a pontoon boat using mostly alcohol free gas. I'd guess its seen about 100 hours at various speeds so far. What can the experts tell me?

 

[Tassie 1]

How much is a new set of plugs compared to a full day on the water?

 

[HotTommy]

How much is a new set of plugs compared to a full day on the water?

So, you suggest I change them before every outing? Thanks for the helpful advice.

 

[Tassie 1]

Well, what does your service book tell you?

if you don't like the replies why ask the question?

it's basic service maintenance,
takes 10 mins...if your slow... to change plugs

 

[Toyelectroman]

According to my mercury vessel view every 100 hours inspect and replace every 300. Me personally i think i will skip the inspection and just replace every 100 hours

 

[HotTommy]

Toyelectroman - that's a cool device. What type of engine does it monitor? .... And sincere thanks for the useful answer.

 

[Toyelectroman]

I think all mercury motors from 2003 and up. I just got it after i put my boat away for winter so i haven't been able to test it out on the water. Cheapest i found was on ebay for $250

 

[HotTommy]

I was curious about the engine because 2 cycle engines tend to go through spark plugs faster than 4 cycle engines. I hope that monitor knows the difference.

 

[dingbat]

Hour based change recommendations usually have little basis in reality.

If I followed my manufacturers recommendation on plug charges I would be changed plugs twice this past April. That’s crazy...

There are three reasons to change a plug:
1. Cracked insulator
2. Oil fouled
3. Excessively worn electrode

Failure modes 1 and 2 are not related to engine hours.

Failure mode 3 is hour related but the longevity of plug electrodes vary by motor.
I regularly put 200 - 300 hours on a set of plugs in a two stroke. A 4 stroke should do better.

 

[HotTommy]

Dingbat, I'm with you. I suspect I'm more likely to damage a plug, the wires or the head by inspecting it too often. I think I'll keep some spare plugs on hand in case it starts running poorly, and change them out every 300-400 hours. After all, the four stroke in my truck gets new plugs every 2,000-3,000 hours.

 

[Tassie 1]

That's fine on a motor that is outside the warranty period,
this motor is a 2016 model and if used recreationally is still under warranty, even if it's not the original owner,

after paying a considerable amount of coin for a motor still in warranty why tempt fate?

if you follow the warranty conditions that are in the owners manual it is harder for Mercury to knock back a warranty claim....not saying they won't try though,

David vs Goliath scenario looms...

been there, done that...not as much fun as it sounds,
Goliath won.

the owners says 12 months for spark plugs

 

[HotTommy]

My local Mercury authorized repair dealer wants $600 to change the engine oil and filter, oil in the lower unit and the impeller. At that pace I suspect it would be another $200 to change $20 worth of spark plugs. I won't have to do too many of these services myself to cover anything a warranty might (or might not).

 

[Tassie 1]

Yes, $600 is a fair few dollars but l would suggest it is in the " carpark " range...give or take a 100 or so... for a service for any brand of 4 stroke,

BOAT = Bring Out Another Thousand,
or Bring Out Another Tool