I've just taken these plugs (PFR7b's) out after covering ~12k in my 'mildly' modded WRX and apart from the tango/OB colouring wondered if someone can assess how they look..?

http://i14.photobucket.com/albums/a3...-24kMedium.jpg

Cylinders #1-4 left to right.

J

BTW here's the OEM plugs they replaced, which had a few metallic deposits, hence the cooler #7's..

http://i14.photobucket.com/albums/a3...kWRXMedium.jpg

 

Spark Plug Diagnosis

 

I had orange colouring on my plugs, the garage put it down to using Optimax.

Cheers

TB

 

Yup. Optimax turns stuff that colour. All the turbos I have peeked in are that colour too.

 

No the orange 'tango'd' look is down to the manganese in OB..

 

Obviously the spark plug diagnosis tells you that you're plugs are fine. A bit orange from the OB/Optimax, but that is apparently normal. The point of getting the right plugs (i.e. hot or cold plugs) is simple in theory. Presuming the engine is OK, in that there is no valve guide/ring wear etc. which leads to oily deposits, then the aim of getting the right "heat" of plug is to prevent carbon deposits building on the electrodes of the plugs. A plug is cooled to an extent by heat transfer through the cylinder head, and also by the incoming fuel/air mixture. Different grades of plug heat up to different temps and counteract the cooling effects by differant levels. A plug that is the right grade for the engine gets hot enough to burn the majority of carbon deposits away, after ignition of the mixture, preventing excessive build up of carbon on the electrode, which in turn can reduce the air gap and prevent efficient combustion. However, too hot and the best case scenario is a burnt out plug. Worst case scenario is a seriously overheating plug, a load of detonation and a knackered piston top/rings/bore etc. Too cold a plug and carbon builds up until the engine starts misfiring because the plug gets fouled up.