www.iFourWinns.com

I havent replaced my spark plugs, cap, rotor, or wires since I bought my boat in 2012. So this would be my 5th season on the same spark plugs. I have put almost 200 hours on those spark plugs.

No problems, and am getting good fuel economy. Just wondering how many hours/seasons everybody accrues before doing a tune up?

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1997 Four Winns Vista 278
T - 4.3l EFI
Kohler 4esz Genset
379 hours as of 8/8/21

I did a quick search online and found a Volvo manual that said to replace every third season.
I would say if you are in salt to follow that guide because the salt air and any drops onto the plug rusts them out and then its a pain to remove. I am sure the electrodes can go years and years.
I broke one off last year from being so rusted out there was nothing left and had to use a back out tool to remove the remaining pieces.

Same goes for cap and rotor they will corrode fast in the salt air 3 years or so is probably a good interval. Wires probably last for a while i haven't changed mine yet and its a 2008.

Fresh water can probably go way longer which sounds like you have done. You can also remove then and check if they look good and no rust then check the gap and put them back.

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--2002 3880 Regal Flybridge | Twin Merc 8.1HO **Seven**
--2003 AB 13 VST Console Inflatable | Tohatsu 40hp TLDI **Phish'n ski**
--310 Mercury Inflatable | 1982 9.9 Johnson

Thanks Babbot. So today I got around to summerizing my engines... Pulled the plugs expecting to find worn electrodes, blown out gaps. Butttttttt I found spark plugs with great looking electrodes and gaps still well within specs. Re-gapped, and reinstalled!

Ill check them next season and maybe then they will be ready. But I cant replace perfectly find spark plugs.

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1997 Four Winns Vista 278
T - 4.3l EFI
Kohler 4esz Genset
379 hours as of 8/8/21

My merc manual says change every 300 hours.
I know yours is a Volvo but in the end, it is a chevy engine.

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The Dance II
2007 278 Vista
6.2L Mercruiser

The only reason why I'd change em sooner is if they looked fouled from the fogging oil or you have an oil consumption issue going on that you're not going to fix anytime soon. I will run the engine, burn off the fogging oil and then take a good look at them, if they are burning clean I'll check the gap and reinstall. My engine is old enough to have points, I check them to see if they are pitted, if so I change them, if not I just check the dwell, timing and idle and go boating. Cap same thing. If just a tiny bit of green corrosion I just brush it off, if it was a lot then I replace.

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88 Four Winns 200 Horizon
4.3 OMC Cobra-4bbl
2002 Walker Bay 10/2012 Suzuki 2.5
2008 Walker Bay 8

1998 Jeep Grand Cherokee 4.0/Selectrac
2007 Jeep Grand Cherokee 5.7 Hemi/Quadradrive II