In Sri Lanka, it doesn't get over 82 c degrees, which is how hot the engine runs. So use the standard heat range plugs.

BP5ES

And remember, new plugs of any brand are better than old worn out plugs.

No need to buy NGK brand, any equivalent plug will suffice. And for you junkyard scroungers, many 4, 6, V8 and V12 engines use the same plugs. I use Champion RCY12 for Chevrolet 5.7 liter, they worked excellently for 5 years.

Spark Plugs include:
•NGK 7734 (BPR5ES)
•NGK 1233 (V-Power BPR5EY)
•NGK 7082 (GP-Series BPR5EGP)
•Autolite 64
•Autolite AP64 (Platinum)
•Autolite APP64 (Double Platinum)
•Autolite XP64 (Extreme Performance)
•Champion 322 (RN11YC4)
•Champion 3322 (Platinum Power)
•Champion 7332 (Double Platinum Power)
•Bosch 4018
•Bosch 4218 (Platinum WR8DP)