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Old 04-08-2019, 07:31 AM   #3
Need For Speed
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Join Date: Feb 2013
Location: Funville
Posts: 2,112
Originally Posted by JFP in PA View Post
Heat range of spark plugs refers to the rate at which the firing tip of the plug transfers heat to the cooling jacket of the cylinder head. "Cooler" plugs transfer it faster, "hot" plugs transfer it slower. This keeps the spark plug temperature high, which allows the plug to self clean and prevent fouling.

The heat range of a given plug should have little to no impact on the car's stead state coolant temperature, that is controlled by the thermostat.
Yes, I understand the heat range of spark plugs. That's why I didn't mention the heat range in my post, but thanks for the info. The difference is in the plug's design, the Bosch plugs have 4 prongs and the NGK has only one prong and the electrode is made of different material at the tip.

Maybe my NGK plugs made a deal with my thermostat? j/k

Or maybe the thermostat has given up and is sticking open all the time now, just happened at the same time I decided to change my plugs?

I really want to get to the bottom of this, as it's much warmer outside now and my car is running cooler since the plug change. I DD my Boxster, even during the winter it would hit 185 on the highway.
2003 Boxster S
| 987 Air Box | K&N Air Filter | 76mm Intake Pipe| 996 76mm TB | 997 Distribution T | Secondary Cat Delete Pipes | Borla Muffler | NHP 200 Cell Exhaust Headers |

Last edited by KRAM36; 04-08-2019 at 07:55 AM.
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