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Unread 03-29-2010, 07:37 PM   #1
the88thpianoman
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2003 WJ 
 
Join Date: Apr 2008
Location: Tampa, FL
Posts: 5,252
Autolite copper vs. autolite single platinum

Probably around 10 or 15k miles ago, I changed out my autolite coppers for autolite platinums because the coppers were worn and the platinums were on sale for only 20 cents more per plug. In the last few thousand miles, I've noticed my mileage getting worse and worse. Tonight, I dumped in most of a can of seafoam and filled up with 89 octane and watched my mpg stay much higher after pressing the reset button (I know the computer isn't necessarily accurate, but it should demonstrate a relative difference).

Now, I've heard it mentioned that platinum plugs run cooler, and it occurs to me that maybe I'm currently making up for this by running the slightly higher octane. I looked up the specs on both plugs.

The copper 985:
Quote:
Center Electrode Material: Inconel
Thread Reach (in.): 0.750
Gasket or Seal Included: Yes
Length (in.): 2.985
Seat Style: Gasket
Center Electrode Core Type: Copper Core
Rib Configuration: Standard
Terminal Top Type: Fixed
Hex Size (in.): 0.625
Number of Electrodes: 1
Insulator Type: Standard
Ground Electrode: Nickel Alloy
Heat Range: 5
Style: Copper Core
Tip Configuration: Copper Core
Center Electrode Firing Tip: Copper Core
Gasket Installed or Loose: Loose
Thread Size/Diameter (mm): 14
Sealing Type: Copper-Glass Seal
Side Electrode: Yes
Resistor: Yes
Resistor Type: 2,000 - 20,000 ohms
And the platinum AP985:
Quote:
Center Electrode Material: Platinum Alloy
Thread Reach (in.): 0.750
Gasket or Seal Included: Yes
Length (in.): 3.175
Seat Style: Gasket
Center Electrode Core Type: Copper Core
Rib Configuration: Standard
Terminal Top Type: Fixed
Hex Size (in.): 0.625
Number of Electrodes: 1
Insulator Type: Standard
Ground Electrode: Nickel Alloy
Heat Range: 5
Style: Platinum
Tip Configuration: Single Platinum
Center Electrode Firing Tip: Platinum Ball
Gasket Installed or Loose: Loose
Thread Size/Diameter (mm): 14
Sealing Type: Copper-Glass Seal
Side Electrode: Yes
Resistor: Yes
Resistor Type: 2,000 - 20,000 ohms
Now, they both spec a heat range 5, but it seems like this could just refer to the physical design of the plug, disregarding the possible (even if minor) temp differences between the different materials.

After doing a good bit of googling and reading, it seems the general consensus is that performance mods to an engine necessitate a cooler plug, but I also get the impression that the air intake, throttle body, and exhaust that I've done are not quite the level of mods that are being talked about.

I think what I will do is run down this tank with the 89 octane and seafoam, then run though another tank of 87 with the platinum plugs still in to see if the cooler combustion lowers my mileage again, then switch back over to copper plugs with 87 octane to see if that affects mileage again. Any thoughts, opinions, or experience you guys would like to share?

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Unread 03-29-2010, 07:42 PM   #2
bigbill888
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1998 XJ Cherokee 
 
Join Date: Nov 2009
Location: michigan
Posts: 954
89 octane runs cooler than 87
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96 ZJ Laredo, 4.0, 242, 230K
95 ZJ Limited, 4.0, 242, 140K
98 XJ Sport, 4.0, 231, 140K
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Unread 03-29-2010, 07:44 PM   #3
the88thpianoman
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Join Date: Apr 2008
Location: Tampa, FL
Posts: 5,252
Quote:
Originally Posted by bigbill888 View Post
89 octane runs cooler than 87
Explain? I always thought higher octane burned hotter...

Edit: Just did some research on that and you are right, higher octane should result in lower combustion temps. Now I don't know what about running higher octane and seafoam is resulting in higher mpg right away. I've not run nearly enough seafoam to clean anything enough to account for it.
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Unread 03-29-2010, 07:49 PM   #4
bigbill888
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1998 XJ Cherokee 
 
Join Date: Nov 2009
Location: michigan
Posts: 954
Higher octane burns slower.
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96 ZJ Laredo, 4.0, 242, 230K
95 ZJ Limited, 4.0, 242, 140K
98 XJ Sport, 4.0, 231, 140K
All work well
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Unread 03-30-2010, 02:05 AM   #5
QuadraTokn
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1930 WJ 
 
Join Date: Dec 2006
Location: Chicago, IL
Posts: 5,047
Ive always read to stick with the copper plugs with the 4.0
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Unread 03-30-2010, 04:26 AM   #6
02Lightning
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1995 ZJ 
 
Join Date: Dec 2005
Location: Dayton, OH.
Posts: 553
Copper plugs produce a better spark because copper conducts electricity better. The only reason they use platinum is for longer life of the plug. Platinum puts more strain on your coil.
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Unread 03-30-2010, 06:35 AM   #7
NeverL8
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2000 WJ 
 
Join Date: Jan 2010
Location: Madison, Mississippi
Posts: 438
go with ngk copper, cheap and good.
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