Learn me about hot and cold spark plugs! - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > General Technical Discussions > Engines & Drivetrain > Learn me about hot and cold spark plugs!

FS: 2007-2013 Jeep Wrangler "HALO" Angel Eye KitFlowmaster's Force II Axle-back exhaust system for the 201FS: Wranger BRIGHT License Plate LED! Just $3! Great value

Reply
Unread 02-08-2011, 03:46 PM   #1
keepishop
Registered User
1989 XJ Cherokee 
 
Join Date: Oct 2008
Location: Seattle
Posts: 3,372
Learn me about hot and cold spark plugs!

I want to know about the effects of hotter and colder spark plugs. All I can find so far is that too cold will result in fouling, and too hot will cause detonation. What is the actual difference in purpose? Are they made for different climates? Compression ranges? Types of driving? Do some perform better cold and some better hot?

Any old spark plug gurus here?

__________________

Current: Black 89 limited, dakota bastard pack, zj coils, 1.5" lift, open cooling swap, bronco 2 carrier, rad fan switch
Rest in Pieces: Red 1990 cherokee dana30/8.25 - v8 zj coils & s10 bastard pack 2.5" lift - 31x10.5r15 tires - v8 zj tierod

Quote:
Originally Posted by talentjeep View Post
Bleed or Quit.
jf irc @ irc.freenode.net #jeepforum
keepishop is offline   Reply With Quote
Unread 02-08-2011, 04:31 PM   #2
5-90
Registered User
1988 XJ Cherokee 
 
Join Date: Sep 2006
Location: San Jose, CA, Hammerspace
Posts: 5,344
Look at the "business end" of the spark plug - see that porcelain bit inside the metal shell?

The difference between a "hot" and "cold" plug is the length of that porcelain nose. A "hot" plug has a longer nose to retain heat; while a "cold" plug has a shorter nose to drain it away.

A "hot" plug is usually used when you have a good deal of carbon fouling, slight oil fouling (be careful here!) or some fuel fouling - the additional retained heat helps to burn the working end of the plug clear.

(I note the care needed with oil fouling - oil getting into the cylinder lowers the overall octane rating of the air-fuel mix, which can lead rapidly to autoignition/detonation.)

A "cold" plug is generally used with forced induction - since compressing air heats it up. This lessens the effect of the retained heat in the spark plug working end, reducing the likelihood of autoignition/detonation due to retained heat.

Any changes in spark plug heat range should only be done one step at a time, and you want to run it for a couple of weeks of daily service to make sure it's not causing any other trouble (particularly if you go one step hotter - it's easy to wander into detonation problems.)

Monitor the colour of the porcelain on the working end of the plug - when everything is running properly, there should be very light deposits and a pale straw yellow colour to the insulator. Learning how to "read" spark plugs is a useful skill - I refer you to Chilton's manuals, which tend to have a very useful colour plate giving this information (it's the same in all manuals - so just find one and study it.)
__________________
"recon" (sic - reckon)(tm) "hihgly"(tm) "seceed"(tm)
"Outback AIDS - Alcohol-Induced Dizzy Spells"
5-90 is offline   Reply With Quote
Unread 02-08-2011, 04:54 PM   #3
keepishop
Registered User
1989 XJ Cherokee 
 
Join Date: Oct 2008
Location: Seattle
Posts: 3,372
Will plugs running too hot prevent good spark?
__________________

Current: Black 89 limited, dakota bastard pack, zj coils, 1.5" lift, open cooling swap, bronco 2 carrier, rad fan switch
Rest in Pieces: Red 1990 cherokee dana30/8.25 - v8 zj coils & s10 bastard pack 2.5" lift - 31x10.5r15 tires - v8 zj tierod

Quote:
Originally Posted by talentjeep View Post
Bleed or Quit.
jf irc @ irc.freenode.net #jeepforum
keepishop is offline   Reply With Quote
Unread 02-09-2011, 09:10 PM   #4
chris142
Registered User
2002 TJ Wrangler 
 
Join Date: Jul 2010
Location: Apple Valley,Ca
Posts: 2,545
Quote:
Originally Posted by keepishop View Post
Will plugs running too hot prevent good spark?
No. The term hot or cold in spark plug talk means how hot the end of the spark plug stays when the engine is running. Too cold and it will get fouled by soot. Too hot and it can cause a hole to be burned in the piston because the gas starts to burn before the plug sparks.

The temp of the plug has no bearing on the spark produced.
chris142 is offline   Reply With Quote
Reply
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.