best engine oil for 20 years old car

If your car’s old enough to vote, the “best” oil is first and foremost the viscosity the owner’s manual asked for—start there before playing chemist. In Australia, many older petrol engines are happy on a quality full-synthetic 5W-40 or 10W-40; if it’s a bit smoky or leaky, a high‑mileage 10W-40 or 15W-40 can help. For diesels, use the manufacturer‑specified diesel rating and a low‑ash formula if it has a DPF—your wallet (and the DPF) will thank you. Pick a reputable brand that meets the car’s stated API/ACEA specs rather than chasing snake oil. Change it every 10,000 km or 12 months (sooner for hard use), and don’t forget the filter. And skip the thick-as-custard miracle goop—it just hides problems and makes cold starts grumpy.