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Spark-plug Question... jc 8-17-02  
I recently did a tune-up, and used a bosch platinum plug. my question is, before my water temp ran about 1/4 warm. now it runs almost at the 1/2 warm. do the platinum plugs run hotter?
Re: Spark-plug Question... Russel 8-18-02  
The heat range of a spark plug doesn't have anything to do with the coolant temp. You didn't say but is it a 454 GM? If it is you may have distrubed the connector on the temp sender which is in the middle of the head above the spark plugs. A previously corroded or loose connection would let the dash guage show a cooler temp than actual. Spark plug heat ranges are built in. It refers to the distance from the tip of the center electrode, thru the ceramic to the metal outside which is what conducts the heat from the tip to the cooler head. A cold rated plug will have a stocky looking short ceramic covering the center electrode, a hot rated plug will have a skinny ceramic that contacts the outside metal deeper inside the plug. Nothing fancy, just an ability to pull heat from the tip to the metal,head,water jacket. Back in the mid 80's there were a few applications that used a long bare center electrode but they didn't serve as they melted. Fortunatly the engines that used them pretty much are all gone now. Platinum tip plugs are IMHO a waste of money and on some applications can cause driveability issues.
Re: Spark-plug Question... RV Wizard 8-18-02  
How was the motor running (power & smooth?) before the tune up? Spark plugs are made for the engine in which they will be installed. It may be that someone previously had a cooler plug than what should have been installed. If you got the right plug for the engine then 1/2 temps are probably the norm.
Re: Spark-plug Question... Sam Watson 8-18-02  
The designation "Hot" or "Cold" as applied to spark plugs refers to the temperature at which the center electrode is designed to operate. The center electrode of a spark plug is cooled by the incoming air/fuel charge, hence a plug whose center electrode is more fully encased in the insulating ceramic surrounding it will be classified as a "Hot" plug, as less of it's center electrode is subjected to the cooling effect of the fuel charge. A "Cold" plug, of course, will have more of the electrode exposed. The reason for all this is to keep the electrode tip within a certain temperature range, as hot as possible without causing preignition or electrode "erosion", ( the transfer of material to the ground electrode). The reason for keeping the electrode hot is twofold, 1. to prevent fouling of the plug,(bridging of the electrodes by combustion products), and 2. electrions are more easily emitted from a hot surface.
Re: Spark-plug Question... Sam Watson 8-18-02  
Thanks Russel, you are correct. I've got to start checking my memory against my manuals.
Re: Spark-plug Question... jc 8-18-02  
Thanks for your replies. I think you might be right about the connection to the sending unit, the motor ran and runs good to this day.
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