Can anyone advise on the correct spark plugs for the 3.5L Mk5 engine?
The service manual specifies L10, and the modern equivalent is the L86C which is a short reach relatively “hot” plug used in many motorcycles.
Does the 3.5L really need a short-reach plug? the cylinder head thread seems much deeper, adequate for a normal plug?
I am currently just using some spare plugs I had in stock from another car, Bosch Super 4 R6, but apparently they are too cold, and I have also been advised they cause problems with old ignition systems, and I should stay with a normal single electrode plug.
I’ve heard numerous fellows in the SS Register say the same thing, Only Champions. It’s a mystery? Yet in a TR6 if you put in Champions it runs poorly until you put in NGK’s!
I measured the thread depth in the head, and its 22mm - so the 3.5L should therefore be using normal length plugs? According to the plug specs at the spares shop, the L10 and equivalent are short-reach plugs with 13mm threads. That means the plugs are recessed, and part of the head plug thread is exposed to combustion?
I noted Graham Jordan’s comments, and also the comments that some plugs work better than others.
I have ordered NGK BP-4ES with are the same heat range, but 22mm thread. I will fit them today and see.
Any observations on why Jaguar specs a short-thread plug?