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I am currently running both a 4 stroke main motor (140 hp Johnson/Suzuki) and a 4 stroke kicker (9.9 hp Evinrude) and up until this year I have always had plugs changed every Fall as part of winterization - same as all my prior 2 strokes. This year the new mechanic at my dealer advised that annual changes were not necessary on the new 4 strokes. I accepted his advice at the time, as my hour meters showed only 32.6 hours on the 140 hp engine and 48.8 hours on the 9.9hp - both well within 100 hour limits indicated in the owner manuals.
I'm now having second thoughts - can anyone confirm this is appropriate, or am I likely to run into problems next year with a similar amount of use. Never had any problems to date and don't want to start !!!

No need to change plugs on a 4 stroke every year since it does not burn a gas oil mix. The plugs will not foul. We have many 4 strokes of different brands stored every year and all with original plugs in them.
JP

I only change mine every 100 hours, and when I take my plugs out they're pretty clean. This is the third winter on these plugs, but I will change them in the spring. I've never had any problems with my Merc 4 stroke.

100 hours or every 2 years which ever comes first

I have experienced over the years, that even though they may look good they need to be changed because the chance of it fouling is lessend,,,

You are out on the water ten miles form the launch DO YOU FEEL LUCKY...


I have found it is better to err on the side of CAUTION and change the plugs my time is worth more than a few spark plugs..

I have a Fitch 200hp and I change my plugs each year whether they need it or not and funny story had a boat last year for service that was down on rpm it ended up being the plugs....

Now if we are talking IRIDIUM and the newer fangle plugs whrer they actually weld a small piece of tungsten or iridium to the eletrode thoase do wear and they also loose those little pieces of tungsten/iridium and that gets past through the engine then. Also the igniton systems are getting so hot these days thus they need for special metals to withstand the heat of the ignition and if your ever look at ther plugs under a magnify glass you can see the erossion not visible with the naked eye.
Also consider the gap of the plug which widens as the plug electrodes wear so the plug NEEDS to be re-gapped at least once a year..

It's easy to assume they are all the same but you don't drive your boat the same as the guy beside you so your conditoins are different thus need different attention.... So change them every 2 years or 100 hours and you will get the good reliable performance from you engine.....

Hi everyone - thanks for input. I'll watch my hour meters closely and will change every 100 hours or two years which ever comes first.

Erie-Eyes wrote:I'll watch my hour meters closely and will change every 100 hours or two years which ever comes first.

So how does everyone monitor hours? Is it just guesswork or is there some other way of doing it? To my way of thinking, I can't say I was out on the water for 6 hours ... add 6 hours to my run meter, because I run only some portion of the time ... stop, start, stop start ...

Suggestions, tactics??

Fisher Dude wrote:

Erie-Eyes wrote:I'll watch my hour meters closely and will change every 100 hours or two years which ever comes first.

So how does everyone monitor hours? Is it just guesswork or is there some other way of doing it? To my way of thinking, I can't say I was out on the water for 6 hours ... add 6 hours to my run meter, because I run only some portion of the time ... stop, start, stop start ...

Suggestions, tactics??

I had two hour meters (one for each motor) installed when I purchased them - originally to monitor break-in times. They record engine running time to tenth of an hour and I note total times every Fall when boat goes to storage which enables me to know exact use each year. Can't remember actual cost of units but they were not expensive.

Fisher Dude wrote:

Erie-Eyes wrote:I'll watch my hour meters closely and will change every 100 hours or two years which ever comes first.

So how does everyone monitor hours? Is it just guesswork or is there some other way of doing it? To my way of thinking, I can't say I was out on the water for 6 hours ... add 6 hours to my run meter, because I run only some portion of the time ... stop, start, stop start ...

Suggestions, tactics??

I'm guessing that JP can probably give you a quote on a Hobbs meter for your boats dash

OK the AVERAGE boat owner puts 35 hours on his/her boat per year, so if you are above avreage and most fisherpersons are then that's when every 2 years comes in no matter what....

It's like this guys the motors worth $XXXXXXX and your weekend is worth $XXXXXXXX most spark plugs are worth $XXX do the math and see how well it adds up

I have a saying "your weekends are for relaxation
NOT FRUSTRATION "

If you use my rule of thumb and go every 2 years you will not go wrong, as sometimes it is the lack of use that is worse than too much...

Here's a scenario, I go 60 minutes to my area(big motor there and back) and then troll for 6 hours (little motor) and do that for ten weekends that's 60 hrs little motor and ten hours big motor.

Now I know that this does not add up to the 100 hours after 2 years but it's which ever comes first BUT is it worth the chance of fouling a plug

I like to err on the side of caution so I don't get stuck out on the water and have to get towed or worse have no-one around to help>>>>


So to sum up every 100 hours or 2 years which ever comes first,

I will change gear oil 3 times a year, I can check the ecm on the motor to see how many hours I have put on the motor and the rpm profile and I am averaging 70 hours per year

The debate is always whether to side on a planned maintenance regime (more costly)or a condition based maintenance regime. While I religiously follow the manufacturers maitemance requirements, Mercury does not advicate a specific change date/ hours dealine for my 75HP 4 stroke. I've now had it in the water 5 summers, with an average of 40-50 hours per season. Each year I do all the plannned maintence (motor oil/filter, lower unit oil, fuel filter Etc.) Each year I check the plugs. 5 years now and not a problem. Again this year I will pull it out of storage, run it up, then check the plugs. If you know how to properly check them, you can rely on the inspection. If not, a change every couple/three years gives you peace of mind. If I am ever in doubt, I consider the affect of blowing any fishinng time and err on the side of caution. My two cents..