reading spark plugs

[356robo]

Just pulled my plugs as part of my annual. I'm not sure if they show running rich or they're too cold. They are Bosch WC5dc+. How can I tell the difference between evidence of running cold or too rich?

Thanks in advance,

Rob

[James Brown]

some good pics would help. go to champion spark plug web site and look at there example of differant plugs

[T77911S]

for ypur reading pleasure. this is info from varius sites. most is from NGK, not me.
but to sumerize, as long as you are not fouling the plug, you are ok for heat range with a W5. turbos and high comp engines use the W3-W4 range.
i have more if you feel the need to read.


In general, a light tan/gray color tells you that the spark plug is operating at optimum temperature and that the engine is in good condition. Dark coloring, such as heavy black wet or dry deposits can indicate an overly-rich condition, too cold a heat range spark plug, a possible vacuum leak, low compression, overly retarded timing or too large a plug gap. If the deposits are wet, it can be an indication of a breached head gasket, poor oil control from ring or valvetrain problems or an extremely rich condition - depending on the nature of the liquid present at the firing tip.




The temperature of the spark plug's firing end must be kept low enough to prevent pre-ignition, but high enough to prevent fouling. This is called "Thermal
Performance", and is determined by the heat range selected. A colder heat range is necessary when the engine is modified for performance, subjected to heavy loads, or is run at a high rpm for a significant period of time.

However, when compression is raised, along with the added power comes added heat.

Since spark plugs must remove heat and a modified engine makes more heat, the spark plug must remove more heat. A colder heat range spark plug must be selected and plug gaps should be adjusted smaller to ensure proper ignitability in this denser air/fuel mixture.

Typically, for every 75-100 hp you add, you should go one step colder on the spark plug's heat range. A hotter heat range is not usually recommended except when severe oil or fuel fouling is occurring.

It is a common misconception that spark plugs create heat. They don't. A heat range refers to how much heat a spark plug is capable of removing from the combustion chamber.

Selecting a spark plug with the proper heat range will insure that the tip will
maintain a temperature high enough to prevent fouling yet be cool enough to prevent pre-ignition. selecting a spark plug in the proper heat range will ensure that the spark plug itself is not a hot spot source.

ignition timing directly affects the firing end temperature of the spark plug.
Advancing the ignition timing prolongs the time to compress the burning gases. The pre-ignition temperature also elevates gradually, since the pressure and
temperature of the combustible mixture is low before ignition. Advancing your
timing elevates firing end temperatures.

the by-product of increased compression is the elevation in cylinder temperatures.

NGK Spark Plugs recommends dropping heat ranges and altering Air/Fuel mixtures and timing as needed. It is very important to dissipate the excess heat from the
combustion chamber in order to prevent pre-ignition.

[Formerly Steve Wilkinson]

With the junk that's in gasoline these days, it's almost impossible to "read" plugs; much of the tutorial above comes from the Good Old Days. Also, to really accurately read plugs you need to run the engine under a strong load and then cut it, not coast down, idle and shut off normally.

[wowzer911]

+1 w/ Steve

[ossiblue]

Originally Posted by Formerly Steve Wilkinson

With the junk that's in gasoline these days, it's almost impossible to "read" plugs; much of the tutorial above comes from the Good Old Days. Also, to really accurately read plugs you need to run the engine under a strong load and then cut it, not coast down, idle and shut off normally.

+1
Steve knows his stuff, follow his advice. Except for looking for oil deposits or obvious signs of misfire, I stopped reading my plugs years ago when lead was removed from gasoline.

[T77911S]

reading plugs is a lost art. most really have no idea how to do it or what they are looking at. i have done a LOT of reading about it. there is a lot of info and a lot of opinions as to what tells you what on the plug. you also need a special magnifying glass to really see what is going on inside the plug. even though it is a lost art, it is still interesting to me. most of the info out there is from drag racers. they are looking for optimum timing and A/F ratio at the end of their runs, so really the best indication of max HP, besides time, is the spark plug.

the main thing i learned from all my reading was about heat range. i use to think hotter meant more power, i have heard others that think the same way. also how timing effects heat in a plug and causes spark knock.

i actually tested a set of W4 plugs. they were very black from city driving and periods of idle. although they were too cold to clean themselves from the rich idleing, they never fouled by the way. i did a 1200 mile trip with them in. i pulled a few when i stopped and they looked very good. the prolonged hiway speed meant a leaner A/F ratio for a long period of time and the plug was able to clean itself. they actually looked as good as when i put them in.
i now have W5, actually BPR7's in and they are fine.

[kach22i]

Pulling plugs on a warm or hot engine may lead to stripping, right?