Spark Plug Heat Range - Cold Water

[jmoser]

I will sometimes use my 1 cyl 4 hp 4 stroke Tohatsu in March or Nov for steelhead when river temps are in the high 30s -40s.<br /><br />Has anyone tried using a hotter range plug in cold weather operation?<br /><br />Have to assume the manufacturers select spark plugs for 'typical' conditions with water temps in the 60s - I would think a hotter range plug would help ignition and cold starting.<br /><br />This is common practice in other applications but outboards are a little 'different,' especially water cooled with no thermostat.<br /><br />Any opinions?

 

[Perfidiajoe]

Re: Spark Plug Heat Range - Cold Water

Spark plug heat range has nothing to do with starting, unless they are fouled because they were too cold. Heat range has to do with transfer of heat to the head from the combustion chamber, cold plugs transfer heat faster hot plugs transfer heat slower. That being said, too hot a plug & it will glow causing preignition, too cold, it won't burn off deposits, when the engine is running. If the engine runs good don't mess with success, if you have problems go up or down 1 range accordingly, but most of the time it is better to look for the problem, such as a stuck thermostat just as an example. good luck, Joe

 

[jmoser]

Re: Spark Plug Heat Range - Cold Water

Hey perf -<br /><br />You are correct; I meant to say running after cold start before warm up, not starting itself.<br /><br />Had a motorcycle that was running way too rich, 1 range hotter plugs helped out there to reduce sooting while I got the jetting fixed.<br /><br />In general I have heard that the small 4 stroke outboards are more prone to running too cool [eg 'making oil' syndrome] than too hot.<br /><br />There will be an obvious difference in cylinder head temps with 40 deg water vs 70, I will have to see how the OEM plug handles the chilly conditions; meantime I will probably buy a spare 'hot' plug for some field trials next fall/winter.

 

[ziemann]

Re: Spark Plug Heat Range - Cold Water

A good indicator of where it is running as far as temperature range is to look at the plug color. You want a nice medium chocolate brown on that Tohatsu. Light gray and you are too hot. Black and oily and you are running too cold. Quality of oil can effect color- idle time vs. running higher RPM's can effect plug color. Without having an exhaust gas temp to indicate where you are at, the best indicator is plug color. I agree that the water temp will have no bearing on what is happening in that cylinder. It all comes down to oil/fuel/air/compression/spark.

 

[ziemann]

Re: Spark Plug Heat Range - Cold Water

OOppps- it is a 4 stroke. I was referring to a 2 stroke. I would still take a look at the plugs to see what they look like. Excess carbon from a rich fuel mixture or some oil that is being burned that is excessively getting past the rings.

 

[dajohnson53]

Re: Spark Plug Heat Range - Cold Water

Originally posted by Z-Man MT:<br /> A good indicator of where it is running as far as temperature range is to look at the plug color. You want a nice medium chocolate brown on that Tohatsu. Light gray and you are too hot. Black and oily and you are running too cold. ....

Should we be seeing the same things in gapless plugs as gapped plugs? I'm fairly familiar with what a normal gapped plug looks like (like you wrote above), but am running a gapless plug for the first time in a kicker I just got. Should they be looking the same? Thanks.