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Marine spark plugs vs normal spark plugs

bgallan

New member
I have an early 60's to 70

I have an early 60's to 70's 40hp Johnson outboard (No ID plate). The spark plugs that were in it were J6C champion. They are also in my 1970 Evinrude 33 hp 33052M. After going to get new plugs and checking with the parts counter for engines between those years. I should be running a J8C (a hotter plug). I'm a little ify on using those. Just want verification from marine experts.
What's the difference between marine and normal plugs?
Thanks
 
"Those engine may use either t

"Those engine may use either the Champion J4C or the J6C plug, gapped at .030.... the 4" and "6" being the heat range. Do noit go any higher than the "6" rating.

The J8C is too hot and will result in damaged pistons. Avoid this plug."
 
"Joe,, the Champion Spark plug

"Joe,, the Champion Spark plug chart specifies the J8C for the 25 hp Johnson. Possibly the lower compression motors need the hotter plug?"
 
BUT does Bombardier or OMC rec

BUT does Bombardier or OMC recommend that J8C plug? Trust me..... don't use it!
 
J8 where in my country (No

J8 where in my country (Norway) mentioned as an alternative for engines WITHOUT thermostat that had low speed/idle problem.
 
Wow I didn't realize that

Wow I didn't realize that spark plugs made that much difference. (So much for just worring about the length). Thanks guys appreciate the input. I'm bringing back the J8's.
But is there a difference between Marine plugs and normal plugs?
 
"ok....good deal......and good

"ok....good deal......and good luck,..maybe i missed interpreted,ur statment....were here,if u need us...."
 
"There is nothing called '

"There is nothing called 'marine' plugs, except for some that have made the metal body stainless to prevent corrosion. Main difference on the plugs used on the same basic engine 'on land' and as 'marine', is that the marine plugs sometimes are 'hotter' due to lower engine temp. In general a hotter plug may give a better idling and less fouling at low speed, but life time may be drastically reduced as it burns down quicker at higher load. Nominal life time for a 2-stroke plug is about 25 hours. In this case You may experience that running J4 might give up to 50 hours, running J8 I would not be surprised it drops to 10 hours before the plug is so far out of specification that the ignition system might be overloaded. Then it is just to hope id does not turn from a spark plug to a glow plug, which will make You end up with a semi diesel!
Good luck."
 
"Blair, I too was fooled by th

"Blair, I too was fooled by the Champion Guide that recommended J8's.. I think the Champion guides are generic and not scrutinized for accuracy. 8's are too hot and they will go elsewhere. (like ebay) I also want to say thanks for the help!"
 
"champion--makes plugs---MARIN

"champion--makes plugs---MARINE plugs,and AUTOMOTIVE plugs,..there is a diff...heat range,suppressive,resister,etc,etc...i dont make plugs,i inst em.....brp(omc)...has a guide,for the proper plugs.......and thru out my 32 yrs,...they send out service bulletins,chging that recommendation,that the public,..never see's...even in 'champ's' guide.............this,is one area,...that experiance....pays off.............thru service bulletins,yrs of installations,and observance,...and updates."
 
JWB well said!!! I guess plug

JWB well said!!! I guess plug life varies around the world here in Aus our customers would be pissed if we had to replace the plugs of a new engine at 20 to 25 hours. I guess we are in the lucky country where plugs last around a 100hours.
 
"-maybe i should be a 'pub

"-maybe i should be a 'public' speaker......naaaa,i better stick to wking on outboards,i guess....i think,..my coors lite,..may interfer!"
 
"Jamie:
It has nothing to do


"Jamie:
It has nothing to do with 'lucky country'.Most likely You may use the plugs up to the time You mention in most countries.
The life time mentioned above it the approx time it takes for the plugs to start loosing its factory specs.Set the gap at .030 and I guess You will be out to at least 0.035 by 25 hours, at 100 hours You are probably far above 0.050! Engine will run, but in reality You are almost 40% off factory spec! Most important the rounding of the center electrode. As user You will normally not notice it from day to day, but I've got the feeling that when You change Your plugs after 100 hours there is a drastic change in engine performance and economy! Reverse it and do a 'laboratory' test and You may discover that the loss of performance starts around the times I mentioned above. It is more a question of how much You want to loose before You change than total breakdown of the plug."
 
"20 hrs?........i never said t

"20 hrs?........i never said to chg them,at any hrs ....just agreed that they need chging..and are one of the overlooked area's.."
 
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