Spark Plugs

[Lucky Penny]

I know that this issue has come up before, but I am still a bit confused. I have a 1977 Mercruiser 5.7 (350CID) 250HP and recently did my annual. Anyway when I replaced the plugs, this year I installed R44T plugs. the book calls for R43T. Question: what effect on operating temp does increasing the heat range of a spark plug. The engine is running about 10F hotter than before. would this be related to the plugs or possibly another problem?

 

[Don S]

Re: Spark Plugs

I would stick with the proper plug. You are probably not understanding what a hotter or colder plug is really doing. Have a look at this from NGK.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqheatrange.asp?mode=nml

 

[Lucky Penny]

Re: Spark Plugs

is that for ngk plug's I alway thought that the higher the number the hotter the plug (AC Delco)

 

[Bifflefan]

Re: Spark Plugs

I would stick with the proper plug. You are probably not understanding what a hotter or colder plug is really doing. Have a look at this from NGK.

http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqheatrange.asp?mode=nml

You always have the coolest stuff....

 

[Bifflefan]

Re: Spark Plugs

is that for ngk plug's I alway thought that the higher the number the hotter the plug (AC Delco)

Different manufacture's number them differently.

 

[Don S]

Re: Spark Plugs

NGK numbers the hot and cold backwards from AC.