spark plug difference?

[Former Member]

What is the difference in spark plugs? If you gap them the same and they have the same depth, what makes one hotter than another? I have always wondered this.

Also, should I run the hottest plug I can find? I did my tune up with the kit from TSC that had plugs in it.

[Lurker Carl]

Hope this helps!

The heat range of a spark plug is it's ability dissipate combustion heat. The heat transfer rate is determined by the length of the ceramic insulator. Additionally, the specific composition of the insulator and center electrode determines the spark plug's ability to absorb and transfer heat.

Spark plugs with different heat ranges tend to look very similar, the differences are internal to the plug. A hot plug has a long internal insulator and absorbs/transfers less heat, but maintains a hotter overall temperature. A cold plug has a short insulator which allows heat to be absorbed and transferred out of the combustion chamber quickly, therefore cooling the combustion chamber.

The purpose of various heat ranges is to keep the combustion chamber at an optimum temperature range. Too cold - carbon deposits quickly form. Too hot - the valves and pistons self destruct. Working tractors usually need a colder plug, trailer queens require a hotter plug because of the type of work each is required to perform.

http://www.ngk.com/charglossary.asp?kw=Heat+range

[PKS]

Carl,

You response was substantiative and very informative. Can you be more specific as to the criterion to be considered a "working" tractor vs a "trailer queen" (for parades/show only?) vs a tractor like mine (not restored) and I assume many others that are used primarily in the spring and summer for various duties (mostly mowing). This would amount to a few or maybe several hours per week but nothing compared to daily farming work. The hotter plug would most likely be the better choice or is there something between the two? Maybe I am dissecting this topic more than necessary.

Paul

[Bigdog]

Paul, that is a good question. I think obviously, show tractors and parade tractors don't come close to building enough heat to keep plugs clean. Even tractors that mow on a regular basis may not see enough work to produce sustained engine operating temperatures. If someone really wanted to get into the subject you could use colder plugs during the working season and hot plugs in the off season.
My personal opinion is to use the hotter plug all the time because I don't think any of today's cubs get worked nearly as hard as they were designed to do. And I don't think there is any downside to the hotter plug for the length of time cubs are used today.

[Lurker Carl]

That's a good question, Paul. It's not so much how often the tractor is used but how it's used.

A working tractor is a machine used primarily for mowing, snow removal, and ground engaging tasks like plowing and cultivating. A trailer queen is a show tractor, you'd also want a hotter plug in tractors that are not subjected to hard labor.

Most times, you can examine the spark plugs and determine if it needs a hotter or colder plug by the color of the deposits on the insulator. Black = need hotter plug. Chalky or blistered = need colder plug. Tan or brown = perfect! Of course, tractors needing a complete tune up, fuel system repairs or overhaul are going to exhibit deposits on the spark plugs as well that moving to a hotter plug may temporarily disguise, but not fix.

[Bill Hudson]

Carl,

Thanks. Very informative and useful.

Bill

[Dusty B]

Just put in a new set of Champion D21's (that's what NAPA had) and that's what mine is going to live with - hot or cold! Starts quick and runs smooth - I'm happy!

[Former Member]

Thanks for the info.

Elmo is a working tractor. I have plowed and disked about 15 gardens so far, am looking for an inexpensive grader blade and a pond scoop. I also have the 22 mower.

Could someone make a good recomendation as to which plug to use? I think the ones I put in are A/C, but I don't know the number. Also, does the gap make a huge difference? I usually set it and then let it spark on the head . Then I adjust to hottest spark.

[Jim Becker]

If the garden work is typical of your use, you would probably do well with Champion D-16. If you also mix in a bunch of light use or idling, go with D-21. Either would probably be OK for you. If you don't like Champion, cross reference to others in those heat ranges. Use whatever you put in until they foul or a tune-up is due again.

You should gap the plugs by the book. Any spark you see with the plug out of the engine is much different than what happens under pressure.

[RedBess]

I can vouch for the hot plug vs cold plug. at 350,000 miles my truck took a quart of oil every 1200 miles. Since the plugs were thick with carbon it was suggested I switch to hot plugs. Sure enough the plugs became coated with browner carbon deposit instead of the coal black stuff, but it caused the engine to ping within 2000 miles of plug cleaning. I switched back to cold plugs and cleaned them every 5000 as a matter of course. With cold plugs and carbon there was no pinging unless I put a hard load on the engine and then there must have been enough residual heat to cause it to ping thereafter on hills where it wouldn't normally do so. I know my example is on the extreme but it was easily a measurable difference. I guess my real lesson is to adapt to the plug's conditions, cleaning either hot or cold at the point just before the engine's performance suffers. hope this doesn't muddle it for you.

[Lurker Carl]

RedBess, experiment with blending higher octane gasoline into your tank to reduce the pinging and still keep the hotter plugs. Carbon build up within the combustion chamber may be raising your compression enough to cause pinging with colder plugs under load as well.