The following are the motor oils I've used in my 12-year old car:
Castrol GTX 20W50 = hirap umarangkada makina; max. speed is 120 kph only :cry:
Mobil1 0W40 Tri-Synthetic = leaked everywhere kahit ni-replace ko na lahat ng seals and gaskets; bye-bye 2000 pesos after a week :x
Havoline Energy 5W30 = leak's gone; improved performance and outstanding fuel economy; max speed increased able to reach 165 kph :D
Idemitsu 5W40 fully-synthetic = performance is good, price is cheap (P260/Liter); not available anymore :?
Castrol Magnatec 10W40 = ok but overpriced for a semi-synthetic oil :shock:
Valvoline All-Climate 5W30 and 10W30 = ok but hirap makahanap
Delo 15W40 = experimentation trip :twisted:
Havoline Fully-Synthetic 5W40 = what I'm currently using; comparable with Havoline Energy although mas fuel efficient ang Energy 8)

On my next oil change I'll be feeding my car's jurassic engine with Mobil 1 Super S 10W40 (semi-synthetic) coz' 10W30/10W40 are the recommended motor oil grades for high mileage car like mine. :mrgreen: